Recent Advances in Electrochemiluminescence AnalysisLingling Li,† Ying Chen,† and Jun-Jie Zhu*

State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University,Nanjing 210093, P. R. China

■ CONTENTS

Novel ECL Systems 358Novel Organic Luminophores 358Novel Inorganic Luminophores 359Novel Nanomaterial System 360

Detection Methodologies and Signaling Amplifica-tion Strategies 361

General Detection Methodologies 361Novel Signal Amplification Strategies 361

ECL Applications 362Metal Ions Detection 362Small Molecules Detection 362ECL Immunoassay 363ECL Genosensors 365ECL Cytosensors 366

Conclusions and Outlooks 368Author Information 369

Corresponding Author 369ORCID 369Author Contributions 369Notes 369Biographies 369

Acknowledgments 369References 369

Electrochemiluminescence (ECL), also called electrogen-erated chemiluminescence, refers to a light emission process

in which species generated at the electrode surface undergoexergonic electron transfer reaction to form excited states thatemit light.1,2 As ECL is emitted through bimolecularrecombination of electrogenerated radicals, its mechanism canbe divided into two categories according to the source of radicals,namely, annihilation mechanism and coreactant mechanism. Asfor the former, radical species are generated from a single emitter,while the latter involves a bimolecular set of electrochemicalreactions between the emitter and a suitable coreactant.3 Theemitter plays a key role in the transformation from electricalenergy into radiative energy. Three types of luminophores,including ruthenium(II) complexes, luminol, and quantum dots(QDs), have been widely utilized in vast majority of ECL studies.In a sense, ECL is the ideal combination of electrochemical

and spectroscopic methods. Therefore, ECL not only holds thesensitivity and wide dynamic range inherited from conventionalchemiluminescence (CL) but also exhibits several advantages ofelectrochemical methods including simplicity, stability, andfacility.4 On the other hand, as a light emission technique, ECLpossesses unique superiorities over other light emissionmethods,such as photoluminescence (PL) and CL. Specifically, incomparison with CL, ECL has superior temporal and spatial

control on light emission. Also, the absence of excitation light inECL promises near-zero background, while PL suffers fromunselective photoexcitation induced background.5 Therefore,ECL has now become a powerful analytical technique and beenwidely used in a large number of environments, ranging fromfundamental studies to practical applications for sensing traceamounts of target molecules.This Review focuses on developments in ECL assays during

2015 to 2016. There have been hundreds of relevant paperspublished during the past 2 years. Therefore, a comprehensivereview is necessary. The aim of this Review is to outline newadvances in areas ranging from new ECL systems, novel sensingmechanisms, strategies for ECL signal amplification torepresentative sensing applications. Lastly, future prospects forthe development of ECL analysis will be discussed. Werecommend readers interested in the general principles of ECLmethods and sensors to refer to previous excellent reviews for abroad scope in this area.1,2,6,7 We tried to be as comprehensive aspossible; however, due to the explosion of publications in thisactive field, as with any review, it is impossible to cover all of thepublished works in the past 2 years. For those papersunintentionally missed, we apologize to the authors in advance.

■ NOVEL ECL SYSTEMSAccording to the luminophores, ECL systems can be generallyclassified into three classes including inorganic systems, organicsystems, and nanomaterial systems. Specifically, the inorganicsystems mainly comprise ruthenium complexes and iridiumcomplexes, and the organic systems includes anthracenes,fluorenes, thienyltriazoles, luminol, and their derivatives.Among these luminophores, tris(2,2′-bipyridine)ruthenium(II)(Ru(bpy)3

2+) and luminol are the most successful with verybroad applications. Since the pioneering work of Bard et al. onECL of silicon semiconductor nanocrystals (also known as QDs)in 2002, the ECL behaviors of various nanomaterials such asQDs, noble metal clusters, and carbon nanomaterials have beenextensively studied. The pioneering works concerning classicinorganic systems, organic systems, and nanomaterial systemshave been reviewed comprehensively before,6 so it will not beelaborated in detail here. We will introduce some novelluminophores either emerged recently or witnessed rapiddevelopment as follows.

Novel Organic Luminophores. Boron-dipyrromethene(BODIPY) dyes have a peculiarly high absorption coefficientand PL quantum efficiency in both visible and near-infrared(NIR) regions due to the electron rich core. Thus, they have been

Special Issue: Fundamental and Applied Reviews in AnalyticalChemistry 2017

Published: November 30, 2016

Review

pubs.acs.org/ac

© 2016 American Chemical Society 358 DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

widely investigated and have application as fluorescent labels andlaser dyes. In addition to the optical properties, BODIPY dyesalso possess diverse electrochemical features with a directcorrelation to the structure design. Bard and co-workerspioneered the electrochemistry and ECL research of severalBODIPY dyes.8−10 Howevere, their ECL efficiency was not ashigh as expected. Highly efficient ECL of a giant BOPIDY dyeincluding a biphenyl linker and two long chain (C8) arms in themeso and alpha positions was investigated by Ding et al.11

Essentially, the presence of the aromatic chains provides a highpossibility for π interaction, thus enabling intermolecularelectronic transition. Blocking at alpha, beta, or meso positionsof the BODYPY core is expected to stabilize the electrogeneratedradicals and therefore to enhance the ECL intensity. This kind ofBODYPY dye showed an ECL efficiency of >80% relative to thatof Ru(bpy)3

2+/trin-propylamine (TPrA) coreactant system,much higher than the other BODIPY dyes. While numerousderivatives of BODIPYs have been designed and their ECL hasbeen investigated, they are often synthesized by time-consumingmethods and in low yield. Formazans have gained growinginterest due to their facile and low-cost synthesis as well astunable absorption, emission, and redox properties.12 Ding andco-workers reported the first systematic study of the ECL of aformazan-derived species, specifically a boron difluorideformazanate dye. The obtained boron difluoride 3-cyanoforma-zanate dye was found to be robust in the presence of TPrA as areductive coreactant, leading to maximum emission at 724 nmwith three distinct, voltage dependent mechanisms.During the past several years, perylene and its derivatives have

attracted considerable attention due to their intrinsic advantages,such as good stability, functional flexibility, fast electron transferrate, outstanding optical properties, and low-cost. Perylene andits derivatives have been proven to be ECL active, but the poorsolubility and radical ion stability problems limit theirapplications in aqueous solution. One of the effective methodsfor solving this problem is to synthesize some new perylenederivatives by introducing hydrophilic groups, such as carboxyland amido, to improve the water-solubility. Chen et al. found thecathodic ECL behavior of the ammonolysis product of 3,4,9,10-perylenetetracarboxylic dianhydride (denoted as PTC−NH2) inaqueous solutions with K2S2O8 as the coreactant for the firsttime.13 On the basis of the fact that dopamine (DA) couldefficiently quench the ECL signals of PTC−NH2, the detectionof DA was achieved. However, PTC−NH2 ECL still suffers fromimperfect luminescent efficiency due to limited water-solubility,which made it depend on exogenous reagent of K2S2O8 ascoreactant. In the same group, a novel covalently cross-linkedperylene derivative (PTC−PEI) composed of polyethylenimine(PEI) and perylenetetracarboxylic acid (PTCA) has been firstinvestigated for cathodic ECL in an aqueous system usingendogenous dissolved O2 as coreactant.14 The PTC−PEIexhibited admirable physical and chemical stability and higherECL efficiency than other perylene derivatives, which held analternative way to construct ECL sensor with improvedsensitivity.Though thiophene molecules are capable of generating ECL,

reports on donor−acceptor π-conjugated (D−π−A) systemsconsisting of thiophene, triazole, and electron acceptor are lesscommon. Moreover, the synthesis of elaborated thienylcompounds is difficult to realize. Ding’s group reported thesuccessful click coupling of 3-azidothiophene and 4-azido-2−2′-bithiophene with a variety of aryl acetylenes to synthesize eightthiophene-based luminophores intended for electrochemical and

ECL study.15 Their ECL behaviors, in both annihilation andcoreactant systems with benzoyl peroxide (BPO), ammoniumpersulfate, and TPrA were also investigated. ECL in theannihilation route confirmed the weak light-emitting nature ofthese thiophenes. However, with the addition of oxidizingcoreactants, the efficiency could be increased. ECL spectroscopyrevealed that the excimer or polymeric excited states were morefavorable in formation than their monomeric excited states,which was tunable based on the applied potentials.Star-shaped conjugated oligomers, a branched molecules

comprising a central core with linear polymer arms, havereceived considerable attention recently since they haveadvantages from both the core and arms in electrical, optical,and morphological properties.16 The π-conjugated oligofluor-enes have received particularly attention due to their blueelectroluminescent properties. However, the electrochemistry ofthese compounds and ECL in solution has not been reported.Bard et al. reported ECL of three 1,3,5-tri(anthracen-10-yl)-benzene-centered starburst oligofluorenes (T1−T3) in acetoni-trile−benzene solution.17 The compounds T1−T3 contain 1,3,5-tri(anthracen-10-yl)-benzene as a core with fluorene as an armfrommonofluorene to trifluorene groups (n = 1−3), generating arigid three-dimensional structure. The formal potentials of thesequential removal or addition of electrons from the core and thearms were evaluated. The mechanisms of multiple electrontransfer were confirmed by chronoamperometry at an ultra-microelectrode, digital simulations, andDFT calculations. Strongblue ECL emission could be generated under ion annihilationcondition from T1−T3, assigned as S-route. These compoundscan be used as promising candidates for ECL materials.

Novel Inorganic Luminophores. To meet the increasingdemand for accuracy and multiplexing in diagnostics, ECLemitters with high efficiency and different emission colors areurgently needed. In comparison with the mostly used Ru-(bpy)3

2+, cyclometalated iridium(III) complexes generally showmuch higher PL efficiency and easy tunability of the emissionenergies, thus becoming an increasingly active ECL subject in thepast few years. By decorating the main ligand and changing thecoordination mode, a series of cyclometalated iridium(III)complexes with 2-phenylquinoline or its derivatives weredesigned, synthesized, and thoroughly investigated by photo-physics, electrochemistry, and ECL.18 By incorporating methylgroups into the 2-phenylquinoline, the corresponding complexesdisplayed lower oxidative potential and higher HOMO energylevels, resulting in considerably stronger ECL emissions than thatof Ru(bpy)3

2+ in acetonitrile solutions. The ECL of cyclo-metalated iridium(III) complexes are mainly studied in organicmedia, and only a few examples in aqueous media or aqueous/organic media have been reported. Cola et al. reported on the PLand ECL behavior of bis-cyclometalated Ir(III) complexes, [Ir-(CN)2(LX)] (CN = cyclometalated ligand, LX = picolinate(pic), acetylacetonate (acac)), in organic solvent and in theaqueous buffer solution used in commercial immunoassays.19

The results showed that modification of the CN ligand could leadto ECL efficiency higher than the commercial Ru-based labels. Inparticular, the complex based on phenylphenanthridine(pphent) as the CN ligand, showed a signal ∼3 times higherthan Ru(bpy)3

2+ employed in commercial equipment.Because of rich structural diversity and remarkable PL

properties, coinage-metal alkynyl complexes have attractedconsiderable attention in the last few decades. However, ECLproperties of coinage-metal alkynyl complexes were completelyunexplored. Wei’s group reported ECL from Ag3Cu5 hetero-

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

359

metallic alkynyl clusters for the first time.20 The synthesizedAg3Cu5 heterometallic clusters showed a windmill-like structurethat could be regarded as a hexagonal bipyramidal rotational axis(Ag3Cu5) and three sails of the windmill consisting of threedpppy ligands (dpppy = 2,6-bis(diphenylphosphino)pyridine).The Ag3Cu5 heterometallic clusters displayed novel PL and ECLproperties, which could be modified by changing the substituenton the alkynyl ligands.The inherent potential initiated excitation and emission

processes of ECL make it promising for multiplexed detectionby generating and detecting multiple emissions simultaneouslyor sequentially in a single system comprising differentluminophores. Previous reports have showed the possibility ofselectively exciting coreactant ECL from a mixture of two ormore transition metal complex luminophores with a distinctdifference between their emission colors and/or oxidationpotentials.21,22 However, annihilation ECL frommixed transitionmetal complex systems in a single solution is yet to be explored.Hogan and co-workers have examined the multicolor emissionsfrom a series of mixed annihilation ECL systems containingRu(bpy)3

2+ and various cyclometalated iridium(III) chelatesexhibiting green or blue luminescence by utilizing an electro-chemical cell coupled with a CCD spectrometer for instanta-neous collection of emission spectra.23 This system showedsimultaneous emissions from multiple emitters, and the ratio ofthese emissions (and hence the overall color of theluminescence) could be tuned though the applied electrodepotentials, exploiting the multiple, closely spaced reductions andoxidations of the reactants. In a later report, they investigated thedetailed mechanism of annihilation ECL from mixed lumino-phores.24 They finally rationalized the results through severalcomplementary mechanisms, including resonance energy trans-fer and various energetically favorable electron-transfer path-ways.Apart from these so-called mixed ECL systems, variable color

ECL from a single molecular emitter has rarely been reported.Hogan et al. recently demonstrated an unusual ECL behavior offac-tris[5-(4-fluoro-3-methylphenyl)-1-methyl-3-n-propyl-[1,2,4]-triazolyl]iridium(III) complex, Ir(mptz)3.

25 Severaldifferent emission colors, including red, green, blue, and nearwhite, could be reversibly generated by changing the appliedpotential. The annihilation ECL mechanism was investigatedusing the 3D-ECL technique, where the ECL spectral profile wascontinuously monitored as a function of potential duringvoltammetric scanning. The results shown that the multicoloredECL in this system arises as a result of the formation of smalltraces of two highly emissive electrolysis products. At least one ofthe products appeared to result from oxidative dissociation of amethyl group from the triazole moiety. In another work, Sun’sgroup synthesized bimetallic Ru−Os complexes, [(bpy)2Ru-(bpy) (CH2)n(bpy)Os(bpy)2]

4+ by connecting normal red Ru-and near-infrared Os-ECL labels through a flexible saturated Cchain to obtain infrared/near-infrared dual-emission ECL ataround 620 nm for Ru and 730 nm for Os.26 Concerted intra- andintermolecular ECL performance and ratiometric ECL detectionwere investigated and utilized to reduce the amount of TPrAcoreactant necessary in the system.Novel Nanomaterial System. Since the first report on ECL

phenomenon of silicon QDs, multifarious QDs including CdS,CdSe, CdTe, ZnS, Ag2Se, and the corresponding alloyed orcore−shell structure QDs have been reported.27−34 Besides,other miscellaneous nanomaterials have emerged and receivedconsiderable attention as effective ECL emitters in recent years,

including carbon nanodots, noble metal nanoclusters, graphite-like carbon nitride, upconversion nanoparticles, and polymerdots.35−43

Gold nanoclusters (Au NCs) represent a new type of ECLnanomaterials due to their discrete electronic energy and directelectron transition. However, the application of Au NCs islimited by their relative low PL and ECL efficiency. Wei et al.localized Au NCs in to 2D layered double hydroxides (LDHs)nanosheets via a layer-by-layer assembly process to obtain AuNCs-based ultrathin films (UTFs), which exhibited an orderedstructure with Au NCs anchoring onto LDH nanosheets denselyand uniformly.38 Because of the host−guest interaction, Au NCswere stabilized in the confined environment of LDH nanosheets,resulting in reduced nonradiative transition and thus enhancedPL and ECL performances. The Wang group recently found anovel mechanism to drastically enhance the ECL by covalentattachment of coreactants N,N-diethylethylenediamine (DEDA)onto lipoic acid stabilized Au (Au-LA) clusters with matchingredox activities.44 This design reduced the complication of masstransport between the reactants during the lifetime of radicalintermediates. The intracluster reactions are highly advantageousfor applications by eliminating additional and high excesscoreactants otherwise needed. The multiple energy states perAu cluster and multiple DEDA ligands also contributed to theenhanced ECL efficiency, which was multifold higher than thestandard Ru(bpy)3

2+ system with excess coreactants TPrA.Since the first report on ECL of poly(9,9-dioctylfluorene-co-

benzothiadiazole) dots in acetonitrile solution, polymer dots(PDs) have aroused growing interest as promising ECLnanoemitters.45 However, because of their poor water solubility,pioneering ECL systems of PDs worked in organic solvent. Thetoxicity of the employed organic solvent make the application ofPDs in the ECL field become a great challenge. Therefore, thesynthesis of hydrophilic CDs and their ECL performs in aqueoussolutions are of paramount importance. Stable, uniform, andhydrophilic PDs were synthesized by capping conjugatedpolymer, poly[2-methoxy-5- (2-ethylhexyloxy)-1,4-phenylenevi-nylene] (MEH-PPV) particles, with Triton X-100.43 For the firsttime, the ECL emission of PDs was investigated in aqueoussolution. The PDs exhibited annihilation ECL activity uponswitching potential between anodic and cathodic potentials inthe absence of coreactants and emitted bright anodic andcathodic ECL emission in the presence of TPrA and S2O8

2−,respectively. The nonsurface state ECL mechanism and easilytunable band gap of the PDs enable the synthesis andapplications of multicolor PDs. Chen et al. found the anodicECL behavior of water-soluble PFO dots (poly(9,9-dioctyl-fluorenyl-2,7-diyl) with Na2C2O4 as coreactant. On the basis ofthe quenching effect of melamine on the ECL signal of the PFO-C2O4

2− system, a new ECL sensing method for melamine wasfurther developed.46 In another report by the same group, H2O2was used as a coreactant to enhance the ECL intensity of the PFOdots.47 Afterward a novel donor−acceptor conjugated polymerbackbone containing silole and 9-octyl-9H-carbazole units wasfurther used to prepare PDs with a nanoprecipitation method.48

The resulting PDs was proved to be a low-potential ECL emitterwith strong anodic ECL emission at +0.78 V (vs Ag/AgCl) in thepresence of coreactant TPrA in aqueous solution, which camefrom the band gap emission of the excited PDs.Metal−organic frameworks (MOFs) are promising ECL active

species because of their high mass transfer capacities andelectrocatalytic efficiency. However, MOF-based electrochem-ical systems are less advanced, let alone ECL investigation. Yin’s

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

360

group reported the ECL from a redox-activeMOF prepared from[Ru(4,4′-(HO2C)2-bpy)2bpy]

2+ and Zn2+.49 The MOF structurewas independent of its charge and is therefore stable electro-chemically. ECL emission with good concentration-dependentresponse toward coreactant of TPrA was observed, which has notbeen reported previously for MOFs. The high ECL emissionsuggested the admirable electron transfer between the MOF andcoreactants. Instead of organic molecules, the use of a metalliccomplex with good luminescence performance as a ligand is apromising way to endow MOFs with excellent ECL activity.Novel luminescence-functionalized MOFs with superior ECLproperties were synthesized based on zinc ions as the central ionsand tris(4,4′-dicarboxylicacid-2,2′-bipyridyl)ruthenium(II) di-chloride ([Ru(dcbpy)3]

2+) as the ligands.50 As a special type ofporous materials, the special structure and properties ofcyclodextrins (CDs)-basedMOFs have been widely investigated.However, the ECL behavior of CD-based MOFs is less reported.We et al. reported the excellent ECL behavior of Pb(II)-β-cyclodextrin (Pb-β-CD) MOF using K2S2O8 as a coreactant.

51

Pb-β-CD also showed unexpected reducing capacity towardAuCl4

− and Ag−. Au and silver nanoparticles (NPs) were in situformed on Pb-β-CD without adding any other reductant.51,52

The doped Au and silver nanoparticles could facilitate the ECLemission and increase the biocompatibility of Pb-β-CD, which isbeneficial to fabricate an ECL biosensor.Nanostructured metal oxides possessing big surface area and

good reaction activity are potential candidates for the fabricationof biosensors. Nevertheless, the investigation about ECL ofnanostructured metal oxides is less well reported. CeO2nanoparticles were first exploited as an ECL luminescentmaterial with K2S2O8 as coreactant by Wei et al.53,54 SinceCeO2 suffers from low electron conductivity, graphene oxide(GO), multiwall carbon nanotubes (MWCNTs), and Au NPswere adopted as carriers of CeO2 to improve the conductivityand the surface-to-volume ratio in these works. Liu et al. revealedthe ECL activity of nontoxic, chemical stable, and low-cost CuOnanowires (NWs) for the first time.55 They prepared reducedgraphene oxide supporting CuO NWs (CuO NWs/rGO) as anovel platform for ECL sensing system. The immobilization ofCuO NWs on rGO could not only ensure recyclability of theECL-based sensor but also further amplify the ECL signal ofCuO NWs. The ECL sensors based on Zn-based II−VIsemiconductors have rarely been investigated due to theinstability and the wide band gap. Wang et al. prepared ZnO-nanocrystal-decorated nitrogen doped graphene (N-GR)composites via one-step thermal-treatment route. Comparedwith ZnO-nanocrystal-decorated undoped graphene (ZnO/GR), the ZnO/N-GR could not only enhance the ECL intensityby 4.3-fold but also move the onset ECL potential morepositively for about 200 mV.56

The development of new highly efficient, biocompatible, andtunable ECL nanoemitters is highly desirable for bothfundamental and bioanalytical applications. Bioinspired nano-materials have attracted increasing interest thanks to theirbiocompatibility, well-defined structures, and capability ofmolecular recognition. Yang et al. at the first time explored theECL properties of cationic dipeptide self-assembled nanovesicles(PNVs).57 The cathodic ECL of the PNVs modified glassycarbon electrodes (GCE) was observed in the presence ofcoreactant K2S2O8. Furthermore, dopamine (DA) was chosen asa model analyte to study the potential of the PNVs in the ECLanalytical application. Since the surface of the PNVs consisted ofaromatic stacking arrangement, DA could be adsorbed on the

PNVs due to strong π−π interaction, which could accelerate theelectron transfer from the DA directly to the PNVs, finallyleading to the enhancement of ECL signal.

■ DETECTION METHODOLOGIES AND SIGNALINGAMPLIFICATION STRATEGIES

General Detection Methodologies. Because of theoutstanding characteristics of ECL, ECL has been considered apowerful analytical technique and growing amounts of ECLbioassays have been constructed in the past several decades forthe detection of miscellaneous target analytes. The approachesfor the construction of sensitive ECL assays can be generallyclassified into five broad categories.7,58 First, the inhibiting orenhancing effect of the target analytes on the ECL reaction bymeans of either energy transfer or electron transfer. Second, thereinforcement or decomposition of ECL emitters via either redoxreaction or surface binding/detachment is also a useful sensingmethod. Third, a strategy to alter the emission of ECL throughthe generation or consumption of coreactants, which is mainlyrealized by enzymatic reactions. Fourth, steric hindrance frombiorecognition reactions or target induced deposition hasenabled the development of a signal-off ECL sensing systems.Last, the recently emerged ECL resonance energy transfer (ECL-RET) has been widely adopted as an efficient sensing strategybased on overlapped spectra of donors and acceptors.Following these sensing approaches, various signal amplifica-

tion strategies have been developed to further boost thesensitivity of ECL sensors. The most common amplificationstrategy is the usage of multifunctional nanomaterials thanks tothe remarkable achievements in nanotechnology and nano-science. Nanomaterials can serve as electrode materials orcarriers for either ECL emitters or recognition elements owing totheir large specific surface area. In addition, functional nanoma-terials cannot only produce a synergic effect among catalyticactivity, conductivity, and biocompatibility to accelerate thesignal transduction but also amplify recognition events withspecifically designed signal tags, leading to highly sensitivebiosensing.59 So far different kinds of nanomateirals have beenused for ECL signal amplification, such as graphene sheets,60−62

carbon nanotubes,63−66 and metal nanomaterials.64,67−70 Cata-lytic reactions are also widely used to amplify ECL by usingenzyme, enzyme mimics, or nanocatalyst signals, such ashorseradish peroxidase (HRP),71−73 and DNAzyme.27,74−76

Despite these burgeoning developments, there is still highdemand for the development of highly sensitive ECL platforms.Novel signal amplification strategies are springing up and havenow become the main driving force of innovation for ECL assays.

Novel Signal Amplification Strategies. At present, theECL detection is usually based on the single emission intensitychanges. False positive or negative errors may interfere with thedetection of trace level analytes due to instrumental or someenvironmental factors.77 Thus, there is an urgent need to seek anefficient ECL system to minimize and even eliminate theseinterference factors. Ratiometric assay, in which the quantifica-tion depends on the ratio of two signals instead of absolutevalues, is an ideal strategy to limit the interference factors vianormalizing environmental variation by self- calibration, whichhas attracted widespread attention recently.40,78 According tomechanism of ECL, the ratiometric ECL systems should includeboth dual-potential and dual-wavelength signal ratiometricassays. Until now, most works adopted the dual-potentialratiometric ECL approach in biological and chemical anal-ysis.74,79−85 Dual-wavelength ratiometric ECL has rarely been

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

361

developed in analytical detection due to the restriction by theluminescence intensity and wavelengths of commonly used ECLemitters as well as the requirement of special detectioninstrument. Xu’s group recently reported a dual-wavelengthratiometric ECL approach based on resonance energy transfer(RET) from graphite-like carbon nitride (g-C3N4) nanosheet(460 nm) to Ru(bpy)3

2+ (620 nm) for sensitive detection ofmicroRNA (miRNA).40 They also developed a visual color-switch ECL sensing platform for quantitative detection of HL-60cancer cells based on different colors of luminol (blue) andRu(bpy)3

2+ (red).86

The vast majority of ECL assays adopted coreactantmechanism since the ECL intensity of most luminophores arenot strong enough. It is well-known that the introduction of anappropriate coreactant into the ECL system can significantlyenhance the ECL intensity and effectively improve the detectionsensitivity. Most of these coreactants are water-soluble smallmolecules, which are usually added into the detection solution toamplify the ECL signal. However, the intermolecular interactionbetween the luminescent reagents and the correspondingcoreactants presents defects in poor stability and low efficiencyof electron transfer.87 Besides, the biological toxicity and volatilenature of those coreactants may sophisticate the operation andincrease the measurement error.87,88 Recently the self-enhancedECL luminophore is proposed by covalently linking the ECL-active luminophore and coreactant into one molecule, which cangenerate enhanced ECL signal through intramolecular inter-action.89−91 The intramolecular interactions between lumino-phore groups and coreactant groups can shorten the electronictransmission distance and improve the luminous stability, thusenhancing the luminous efficiency. These self-enhancedapproaches provided a new perspective to construct sensitiveECL system for detection of target analytes.50,89,92−95

■ ECL APPLICATIONSMetal Ions Detection. Accurate and reliable detection of

metal ions is thoroughly significant due to both deficiency, andoverdose of them will cause the imbalance of homestasis andsubsequent severe diseases. Lead ion (Pb2+), as one of them, isone of the most hazardous metal pollutants. Therefore, rapid andsensitive detection of Pb2+ is of great significance for environ-mental protection as well as disease prevention and treatment. Asensor for the detection of Pb2+ was constructed by immobilizingCdS QDs and capture probe on gold nanodendrites (Au NDs)modified indium tin oxide (ITO) electrode.96With Pb2+-inducedactivation of DNAzyme, the Ag/ZnO coupled structures wereclose to the surface of the electrode to catalyze the reduction ofH2O2, the coreactant for cathodic ECL emission, leading to adecrease of ECL intensity. Yuan et al. constructed an ECLbiosensor using N doped carbon dots (N-CDs) in situ electro-polymerized on GCE as luminophores and Pd−Au hexoctahe-drons (Pd@Au HOHs) as enhancers for the detection ofintracellular Pb2+.36 In this work, Pd@Au HOHs−DNAdendrimers with were formed on N-CDs modified electrode,which could couple Pb2+ in the form of Pb2+-stabilized G4structure. Therefore, the ECL intensity of the N-CDs wasquenched by Pb2+. In another work, a novel ECL-RET systemfrom O2/S2O8

2−to a kind of amino-terminated perylenederivative (PTC-NH2) was demonstrated and then applied toconstruct a ratiometric aptasensor for Pb2+ detection. A sensitiveECL-RET switch was obtained where the Pb2+ dominated theamount of PTC-NH2 by generating G-quadruplex structure. Theratio of donor/acceptor peak intensity could be regulated upon

the concentrations of Pb2+, thus Pb2+ could be quantitativelydetected.79

Mercury exposures can cause many adverse health effects inhuman and wildlife, even at a low concentration level. Therefore,the sensitive detection of Hg2+ is of great importance. Liu et al.developed an ECL sensor with a high-intensity charge transferinterface for Hg2+ detection based on Hg2+-induced DNAhybridization.97 dsDNA with thymine-Hg2+-thymine (T-Hg2+-T) base pairs exhibited more facile charge transfer, which couldaccelerate the electron transfer performance and increase theECL intensity. The increased ECL signals were found to belogarithmically linear with the concentration of Hg2+. Huang etal. prepared a sensitive ECL biosensor for the detection of Hg2+

by self-assembling mercury-specific oligonucleotide on thesurface of Au NPs modified ITO electrode.98 The binding ofHg2+ through T-Hg2+-T coordination could induce a con-formation change of the oligonucleotide from linear chain tohairpin. The dual-function oligonucleotide served as the probe toHg2+ but also a carrier for the conjugation of multiple ECL signal-generating molecules. A detection limit of 5.1 pM Hg2+ wasoutstanding from the interference of 10 other metal ions. On thebasis of the strong and stable T-Hg2+-T interaction and thequenching effect of Hg2+ on the ECL of N-(aminobutyl)-N-(ethylisoluminol) (ABEI), an ECL aptasensor to detect Hg2+ wassuccessfully developed.99

As a key component of vitamin B12, cobalt is vital in humansand biological systems. Li et al. fabricated a dual-potentialratiometric responsive ECL sensor for Co2+ ion detection.100

Nitrogen-doped graphene quantum dots (NGQDs) could emittwo ECL signals at both positive and negative potentials with theparticipation of dissolved oxygen. In the presence of Co2+ ion, theanodic ECL intensity of NGQDs increased dramatically(amplified about 15 times) while the cathodic ECL decreasedobviously. On the basis of the ratio of two ECL intensities, aratiometric sensor for Co2+ ion was developed and has beenapplied to detection of Co2+ in real water.When the concentrations of interfering metal ions are several

times higher than that of the target metal ion, it is almostimpossible to distinguish which metal ion changes the ECLsignals in real sample detection. Zhang and co-workers reportedthat the dual-ECL signals could be actuated by different ECLreactions merely from graphite-phase polymeric carbon nitride(GPPCN) nanosheets at anodic and cathodic potentials,respectively.101 They found that different metal ions exhibiteddistinct quenching/enhancement of the ECL signal at differentdriven potentials, possibly because of the different energy-levelmatches between metal ions and GPPCN nanosheets andcatalytic interactions of the intermediate species in ECLreactions. On the basis of the preliminary “fingerprint” (ECLquenching or enhancement at cathodic and anodic potentials,respectively) and the linear relationship between the ECLintensity and different concentrations of the metal ions, the false-positive result could be largely avoided without labeling andmasking reagents. Especially, Ni2+ ion showed highest quenchingefficiency at the cathodic potential range due to the best energymatch. Meanwhile, unlike most metal ions, Ni2+ could result inenhancement of the anodic ECL intensity of GPPCN. Thus, theproposed dual-ECL signals of GPPCN was applied for thedetection of trace Ni2+ ion with a detection limit of 1 nM in tapand lake water.

Small Molecules Detection. Recently, increasing interesthas been drawn to the determination of H2S because it has beenrecognized as an endogenous gas signal molecule. Ye et al. used a

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

362

novel ruthenium complex, [Ru(bpy)2(bpy-DPA)]2+ (where bpy

= 2,2′-bipyridine and bpy-DPA = 4-methyl-4′[N,N-bis(2-picolyl)aminomethylene]-2,2′-bipyridine) as a recognition unitto construct a reaction-based turn-on ECL sensor for selectivedetection of extracellular H2S in rat brain.102 The ECL of[Ru(bpy)2(bpy-DPA)]

2+ could be quenched by Cu2+ via theformation of [Ru(bpy)2(bpy-DPA)Cu]

4+. The [Ru(bpy)2(bpy-DPA)Cu]4+/Nafion/GCE sensor demonstrated enhanced ECLsignal after reacting with volatile H2S due to the high-affinitybinding between sulfur and Cu2+, returning to [Ru(bpy)2(bpy-DPA)]2+/Nafion/GC. The changes of ECL signal at the sensordepended linearly on the concentration of Na2S in the rangefrom 0.5 to 10 μM, with a detection limit of 0.25 μM.In an ECL detection system, the amount of light generated

directly depends on the concentration of the luminophore butalso of the coreactant. Sojic et al. designed and prepared a seriesof amine based coreactants integrating boronic acid function asreceptor units.103 They demonstrated that the recognition of thesaccharide could modify both the structure and the reactivity ofthe coreactant and thus the resulting ECL emission. Besides,excellent differential selectivity for D-glucose and D-fructose wasachieved by tuning the linker length of a bis-boronic acid aminecoreactant.Organophosphates (OPs) have raised serious human health

and environmental concerns. Therefore, effective OPs analysis isof great importance. Wang et al. designed a novel “smart” ECLswitch-type OP sensor by employing the specific binding oftarget pesticide molecules on graphene oxide (GO) decorated bycobalt phthalocyanine (CoPc) and using ethanol as the radicalscavenger on a GO−CoPc-based sensing platform, whichgenerates an “ON1−OFF−ON2” ECL response.104 Yuan’sgroup constructed a signal on an ECL biosensor using β-cyclodextrin functionalized g-C3N4 as the luminophore forsensitive OPs detection based on the enzyme inhibition of OPs,showing that the consumption of coreactant triethylaminedecreased with a lessening of the acetic acid in situ generatedby enzymatic reaction.105

A new ruthenium(II) complex basedmultisignal chemosensor,Ru-Fc, was reported for the highly sensitive and selectivedetection of lysosomal hypochlorous acid (HOCl) in living celland laboratory animal samples.106 Ru-Fc was weakly luminescentbecause the MLCT (metal-to-ligand charge transfer) state wascorrupted by the efficient PET (photoinduced electron transfer)process from Fc (ferrocene) moiety to Ru(II) center. Thecleavage of the luminescence quencher moiety Fc by a HOCl-induced specific reaction led to elimination of PET, which re-established theMLCT state of the Ru(II) complex, accompaniedby remarkable PL and ECL enhancements.Sensitive and accurate detection of antibiotics plays a

paramount role in various fields including environment andfood safety. A sensitive sensor for the determination of selectednitrofurans in animal feed samples, including furaltadone,furazolidone, and nitrofuratoin, was proposed with use ofCdTe QDs enhanced ECL of the Ru(bpy)3

2+ system.107 It wasfound that the induced ECL from the Ru(bpy)3

2+ CdTe-QDssystemwas inhibited by the presence of selected nitrofurans. Thisquenching effect of nitrofuran antibiotics was found to beselective and concentration dependent and was observed to havea linear relationship over a wide concentration range. In addition,the proposed ECL method was successfully applied to detect thetotal residuals of selected nitrofuran residues in animal feedsamples with satisfactory results. A novel triple-amplificationECL assay was designed for detecting chloramphenicol (CAP)

based on single-strand DNA-binding protein (SSB) andEnVision reagent (EV) labeled on Au NPs (EV−Au−SSB) asnanotracer and exonuclease-assisted target recycling.108 In theEV−Au−SSB, Au NPs could effectively enhance the ECLintensity of CdS NCs by by surface plasmon resonance.Moreover, the combination of Au NPs and EV could furtheroxidize CdS NCs for the ECL signal enhancement via thecatalysis of H2O2 to generate a large number of reactive oxygenspecies. The developed aptasensor exhibited the linear responserange from 0.0001 and 10 nM with a detection limit of 0.03 pM(S/N = 3) for CAP.

ECL Immunoassay. ECL is powerful and promising forsensitive and selective determination of analytes in clinicalsamples owing to the integration of the high affinity of antigen−antibody interaction with the intrinsic properties of ECL. Thedetermination of cancer markers associated with certain tumorsplays an important role in diagnosing cancer diseases. Prostate-specific antigen (PSA) is the best serum marker currentlyavailable for the diagnosis and targeting of prostate cancer at anearly stage. Wei et al. used Ag NPs doped Pb(II)-β-CD (Ag@Pb(II)-β-CD) as a substrate material to construct a new type oflabel-free immunosensor for detecting PSA.52 Wei et al.developed a CeO2-matrical enhancing ECL sensing platformfor PSA based on the Bi2S3-labeled inverted quenching system.

53

In this work, amidogen graphene (NH2-Gr) and Au NPsfunctionalized CeO2 NPs (NH2-Gr/Au@CeO2) exhibitedstrong ECL activity which could be quenched efficiently bybismuth sulfide Bi2S3. By using NH2-Gr/Au@CeO2 as the ECLresponse substrate layer and Ag NP functionalized Bi2S3 ascarrier of the secondary antibody, a novel sandwich ECLimmunosensor was constructed for the detection of PSA with alow detection limit of 0.3 pg mL−1. Du and co-workers proposeda label-free immunosensor for PSA by using ECL active EuPO4nanowire.109

Self-enhanced signal amplification strategy has been success-fully adopeted for the construction of ECL immunosensors byYuan’s group. An intramolecular self-enhanced ECL immuno-sensor based on palladium nanowires (PdNWs) was constructedfor carcinoembryonic antigen (CEA).88 PdNWs, with highspecific surface area and superior electrocatalytic activity, weresynthesized with a green procedure by using Lentinan (LNT) asa stabilizer and reducing agent. The obtained PdNWs wereapplied to immobilize an enhanced amount of tris(4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium(II) dichloride (Ru-(dcbpy)3

2+) functionalized polyamidoamine (PAMAM) den-drimer to form a new electrochemiluminescent derivative(PdNWs−PAMAM−Ru). In this way, the Ru(II) luminophoreand its coreactive groups (amine groups in PAMAM) existed inthe same complex. The obtained complex (PdNWs−PAMAM−Ru), as a new self-enhanced ECL derivative with enhancedluminous efficiency, was applied to construct a “signal on”sandwiched ECL immunosensor by using Au NPs as ECLsubstrate and PdNWs−PAMAM−Ru as a signal tracer. In thefollowing report, a new manganese ions doped zinc oxide poroussix arises column nanorods (Mn-ZnONRs) were used asexcellent nanocarriers of Ru(dcbpy)3

2+ luminophore andcoreactive agent L-Lys to prepare self-enhanced ECL complexfor construction of sandwiched ECL immunosensor.110 Anotherself-enhanced ABEI derivative-based ECL immunosensor wasconstructed for the determination of laminin (LN) using PdIrcubes as a mimic peroxidase for signal amplification.89 L-cysteine(L-Cys) and ABEI were immobilized on the PdIr cubes to formthe self-enhanced ECL nanocomplex (PdIr-L-Cys-ABEI), where

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

363

PdIr cubes could effectively catalyze coreactant H2O2 decom-position and thus enhance the ECL intensity of ABEI. Thedeveloped strategy resulted in a significantly enhanced ECLsignal output. By covalently linking luminescent [Ru-(dcbpy)2dppz]

2+ with N,N-diisopropylethylenediamine(DPEA) through amidation reaction, Yuan et al. also designeda novel “light-switch” molecule ([Ru(dcbpy)2dppz]

2+-DPEA)with self-enhanced ECL property, which was almost nonemissivein aqueous solution but brightly luminescent after intercalatinginto the DNA duplex.94 As shown in Figure 1, biotin labeled

DNA dendrimer (the fourth generation, G4) was prepared fromY-shaped DNA by a step-by-step assembly strategy, which couldserve as excellent nanocarriers providing abundant intercalatedsites for [Ru(dcbpy)2dppz]

2+-DPEA. The self-enhanced nano-composite (G4-[Ru(dcbpy)2dppz]

2+-DPEA) could well bindwith streptavidin labeled detection antibody (SA-Ab2) due to theexistence of abundant biotin. Through sandwiched immuno-reaction, an ECL immunosensor was fabricated for sensitivedetermination of N-acetyl-β-D-glucosaminidase (NAG). Theseworks all utilized nanomaterials to hold luminophore andcoreactive agent. They also used self-enhanced ECL reagent,synthesized by covalently linking bis(2,2-bipyridyl)(4′-methyl-[2,2′]bipyridinyl-4-carboxylicacid) ruthenium(II) (Ru-(bpy)2(mcbpy)2+) with TPrA, as a precursor to preparenanorods ([Ru(bpy)2(mcbpy)2+-TPrA]NRs) with high lumi-nous efficiency.111 Then Pt NPs functionalized [Ru-(bpy)2(mcbpy)2+-TPrA]NRs were used to load the detectionantibody (Ab2), while the Au/Pd dendrimers (DRs) withhierarchically branched structures were used to immobilizecapture antibody (Ab1). On the basis of sandwiched immuno-

reactions, a simple and sensitive “signal-on” immunosensor isconstructed for the detection of NAG.Jiang et al. reported a QDs based potential-resolved ECL

immunosensor to realize simultaneous detection the modelmolecules of alpha fetoprotein (AFP) and its AFP-L3 isoform.112

AFP-L3%, a novel biomarker for hepatocellular carcinomalaboratory diagnosis, was calculated accordingly. Because ofdifferent surface microstructures, dimercaptosuccinic acidstabilized CdTe (DMSA-CdTe) QDs and TiO2 NPs-glutathionestabilized CdTe (TiO2-GSH-CdTe) QDs showed a largedifference of ECL peak potential (∼360 mV). Two separateinterfaces of ITO electrodes were modified to specificallyrecognize AFP and AFP-L3, respectively. By immobilizing theDMSA-CdTe QDs-anti-AFP and TiO2-GSH-CdTe QDs-anti-AFP-L3 on ITO electrodes surface, combined with the enzymaticamplification strategy, on-step label-free test of AFP-L3% couldbe realized.Ugo et al. reported the design of a novel immunosensor for

anti-transglutaminase type-2 antibody (anti-tTG) IgG determi-nation based on an ECL readout, using membrane-templatedgold nanoelectrode ensembles (NEEs) as a detection plat-form.113 A major originality of this approach was the physicalseparation between the location of the initial electrochemicalreaction at the Au NEEs (i.e., oxidation of the coreactant) fromthe ECL-emitting region where the luminophore label wasimmobilized on the polycarbonate (PC) substrate, as shown inFigure 2. Specifically, the capturing agent tTG was at first bound

onto the PC of a NEE to react with the target analyte anti-tTGIgG antibody and then realize the immobilization of astreptavidin-modified ruthenium-based ECL label via reactionwith a suitable biotinylated secondary antibody. Thanks to thecustomized architecture of the platform, the TPrA coreactant wasoxidized at the nanoelectrodes, and the resulting radicals diffusedall over the geometric area of the NEEs to reach the Ru(bpy)3

2+

label on the PC to produce ECL. The immunosensor providedECL signals scaled with anti-tTG concentration with a detectionlimit of 0.5 ng mL−1. A particular advantage of this design is that

Figure 1. (A) Preparation of G4-[Ru(dcbpy)2dppz]2+-DPEA; (B)

schematic diagram of the construction of the immunosensor and theresponse mechanism. Reproduced from Wang, H.; Yuan, Y.; Zhuo, Y.;Chai, Y.; Yuan, R. Anal. Chem. 2016, 88, 5797−5803 (ref 94). Copyright2016 American Chemical Society.

Figure 2. Scheme showing the design of the immunosensor (not toscale). Reproduced from Habtamu, H. B.; Sentic, M.; Silvestrini, M.; DeLeo, L.; Not, T.; Arbault, S.; Manojlovic, D.; Sojic, N.; Ugo, P. Anal.Chem.2015, 87, 12080−12087 (ref 113). Copyright 2015 AmericanChemical Society.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

364

the ECL emission is obtained at much lower operative potential,thus reducing significantly the possible interference from sidereactions in samples containing oxidizable species. It can alsominimize possible electrochemical damage of sensitive bio-molecules and reduce the oxide formation on Au or Pt electrodesurfaces.ECLGenosensors.The past 2 years has witnessed substantial

advances toward the development of high-performance ECLgenosensors. Multifarious sensing strategies have been devel-oped for the achievement of good sensitivity and selectivity.Designed DNA can be used to generate DNAzyme, which is a

kind of sequence-specific nuclease catalyst for certain bio-chemical reactions. DNAzyme is very popular in ECLgenosensors for important signal amplification strategies suchas target recycling amplification (TRC) and rolling circleamplification (RCA).114,115 Yuan et al. developed an ECLplatform for microRNA using the target-cycling synchronizedRCA strategy and in situ generated electrochemiluminescentsilver nanoclusters (Figure 3).37 They designed a DNA circular

template consisting of a guanine-rich region and a binding regionfor target-cycling synchronized RCA. A “P” junction structurewas formed after the binding region hybridized with targetmicroRNA and the primer which could trigger the RCA process.Meanwhile, target microRNA was released and acted as anothertrigger of RCA. The product DNA possessed tandem periodiccytosine-rich sequences which served as ligands for electro-chemiluminescent silver nanoclusters generation. Thus, the ECLintensity from silver nanoclusters was positively related to targetmicroRNA concentration. By subtly designing DNA sequences,they also developed a DNA walking machine for ECLgenosensor.116 The designed DNA nanostructure tracks hadfour overhang sequences complementary to the walker (targetDNA) and modified with ECL labels, and the tracks were self-assembled on the electrode surface. The target DNA hybridizedwith the complementary tracks and formed specific recognitionsites for a restriction enzyme (Nt.AlwI) which could cleave theoverhang sequences, lose ECL labels, and drive directionalmovement of the target DNA. Along with the target DNAwalking through the track, all the ECL labels were released andprovided a “signal-off” ECL platform. By replacing the ECLlabels modified on the overhang sequences with quenching

molecule ferrocene, they also built a “signal-on” ECL plat-form.117

By embedding or labeling ECL emitters such as Ru(bpy)32+ to

DNA sequences, advanced ECL genosensors are designed.118,119

For example, a Ru complex tagged thiolated shared-stem hairpinDNA was designed and self-assembled onto GO/Au NPsmodified electrode surface to build an “signal-on” ECL biosensorfor the detection of specific DNA sequence.120 Without targetDNA, the ECL of Ru complex was quenched by GO due to theshort distance between them. While, once the target DNAhybridized with hairpin DNA, the hairpin structure was openedand the tagged Ru complex became far away from the grapheneoxide, leading to the increase of ECL intensity. Chen’s groupreported a dual-wavelength ECL ratiometric platform formicroRNA detection using the ECL-RET between g-C3N4nanosheets and Ru(bpy)3

2+.40 The Au NPs modified g-C3N4nanosheets were coated on the electrode surface to give strongand stable ECL emissions, which was well matched with theabsorption peak of Ru(bpy)3

2+ and could stimulate its ECLemission RET effect. Then Ru(bpy)3

2+ was labeled on DNA toform probe DNA-Ru(bpy)3

2+ and was further introduced bytarget microRNA to hybridize with capture DNA on electrodeand realize the RET process. On the basis of the quenching ofECL signal at 460 nm and increasing at 620 nm, a dual-wavelength ratiometric platform was built.In recent years, certain designed DNA has been applied for

building biomolecular Boolean logic gates in ECL biosensors.Biomolecular Boolean logic gate is a type of molecularcomputing device which has aroused great interest amongresearchers. Chen and co-workers reported an ECL sensingstrategy for protease and nuclease using biomolecular Booleanlogic gates.121 First, they regulated the diffusive flux of coreactantby the target-triggered desorption of programmable polyelec-trolyte film on the ECL emitting g-C3N4 film, which induced therecovery of ECL signal. Different substrates programmed in thepolyelectrolyte film responded to protease and nuclease,respectively. By programming OR and AND DNA logic gatesin the polyelectrolyte film, this biosensor could simultaneouslyanalyze proteases and nucleases in one sample. Anotherbiomolecular logic device was established on the molecularlyimprinted polymer (MIP) film electrodes.122 The MIP film waselectropolymerized with chloramphenicol (CP) as the templatemolecule on the surface of Au electrodes. After CP removal,DNA acted as an enhancer to the CV and ECL peaks fromRu(bpy)3

2+ solution, while ferrocene methanol (FcMeOH)acted as a quencher. Thus, DNA, CP, and FcMeOH were threeinputs and the corresponding CV and ECL signals were outputs,achieving the 3-input/3-output and 3-input/5-output logic gates.Similarly, a 3-input/4-output logic gate system based on thedamage of natural DNA was also reported.123

Nanomaterials with different chemical components, sizes,shapes, and unique properties have been adopted in ECLgenosensors, bringing considerable improvement in sensitivityand stability. In the recent 2 years, a number of advanced ECLgenosensors based on multifunctional nanomaterials have beenreported.67,124 Wang et al. reported an ECL and PL dualdetection channeled aptasensor based onN-doped GQDs@SiO2nanoparticles as a signal indicator.125 Fe3O4−Au magnetic beadswere used as nanocarriers for N-doped GQDs@SiO2 NPsthrough specific DNA hybridization between an aptamer andcapture DNA. Upon target molecules incubation, N-dopedGQDs@SiO2 NPs were released from the magnetic electrodesurface into solution. Because of the good ECL and fluorescence

Figure 3. Schematic Illustration of (A) the principle of target-cyclingsynchronized RCA and in situ electrochemical generation of Ag NCs,(B) Preparation of the circular template, and (C) ECLmechanism of AgNCs/S2O8

2−-based ECL system. Reproduced from Chen, A.; Ma, S.;Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem. 2016, 88, 3203−3210 (ref 37).Copyright 2016 American Chemical Society.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

365

properties of N-doped GQDs@SiO2 NPs, the dual detectionchanneled aptasensor was thus fabricated. In another ECLaptasensor, CdTe QDs were used as the ECL emitters andsemicarbazide (Sem) was used as coreaction accelerator topromote the ECL reaction of CdTe QDs/S2O8

2− system.126 TheCdTe QDs were modified onto C60 nanoparticles to get CdTeQDs@C60NPs nanocomposites, which were coated on theelectrode surface. For the accelerator probe, hollow Aunanocages were prepared and functionalized with semicarbazideand Au nanopaticles via layer-by-layer assembly to get multi-layered nanomaterials of (AuNPs-Sem)n-AuNCs which couldimmobilize a great deal of detection aptamers. With the goodperformance of two kinds of nanocomposites, this aptasensorshowed great sensitivity with a detection limit of 0.03 fM. On thebasis of this strategy, they subsequently reported a similar ECLaptasensor with graphene surface in situ generated CdTe as ECLemitter and a kind of perylene derivative as the coreactionaccelerator.127 Zhou et al. reported an ECL method for DNAmethyltransferase (M.SssI MTase) activity detection based onthe ECL emission of CdS QDs and the glucose oxidasemimicking effect of gold nanoparticles for coreactant gener-ation.128 In this method, dsDNA containing special sequence wasimmobilized on CdS QDs modified electrode surface, followedby methyltransferase treatment to catalyze DNA methylation.Once the special sequence was methylated, the restrictionendonuclease could not recognize and cut off the specialsequence. Then Au NPs were combined with the dsDNA whichwere not cut off and catalyzed the oxidation of glucose to produceECL coreactant hydrogen peroxide for CdS QDs, giving ECLsignal corresponding to the DNA methyltransferase activity.Conventional ECL luminophores like Ru(bpy)3

2+ and luminolhave the advantage of strong ECL emission. Some researcherscombined nanomaterials with these conventional ECL lumino-phores to get nanocomposites with advantages fromboth.60,90,129 For example, Zhao and co-workers reported aone-pot synthesis method of GO/Ag NPs/luminol compositeand used it to build an ECL biosensor for the detection of DNAmethyltransferase activity.130 This nanocomposite could assem-ble large amount of luminol and the Ag NPs could furtherenhance luminol to give strong ECL signal. The nanocompositeswere immobilized to azide-terminated dsDNA modifiedelectrode, and once the DNA hybrid was methylated andcleaved by Dpn I endonuclease, GO/Ag NPs/luminolcomposites were released and caused significant reduction ofthe ECL signal. Similar composites consisting of luminol, AgNPs, and graphene oxide were applied in another ECLaptasensor.131 Yuan’s group developed a Ru complex and hollowgold nanoparticles branched-poly(N-(3-aminopropyl)-methacrylamide) hydrogel composites (pNAMA-Ru-HGNPs)as an ECL label in an aptasensor for thrombin detection.93 ThepNAMA-Ru-HGNPs hydrogel composites served as effectivecarriers for a thrombin binding aptamer to form ECL probes. Onthe other hand, dendritic gold nanoparticles modified carbonnanotube-nafion were coated on the electrode surface as anenhancer to amplify the ECL signal and matrix for captureaptamers immobilization.The development of a simple, fast, portable, and cost-effective

ECL device is the main challenge for the industrialization of ECLgenosensors. Rusling’s group developed an ECL microfluidicarray featuring a 64-nanowell chip with polymer [Ru-(bpy)2(PVP)10]

2+ as an ECL emitter for measuring DNAdamage.132 This microfluidic chip had 64 printed toner inknanowells which could capture 1 μL of solution by virtue of a

hydrophilic bottom and hydrophobic wall. Films of enzymes,DNA, and [Ru(bpy)2(PVP)10]

2+ were achieved via alternativeelectrostatic layer-by-layer fabrication. ECL activation anddetection were run by passing reaction solutions through thearray chamber inside a dark box with a charge coupled device(CCD) camera. Besides, the LC−MS/MS technique was used asa companion method to detect the nucleobase metaboliteadducts. Moreover, a digital microfluidics ECL device was builtfor microRNA analysis by Shamsi et al.133 In this device, ECLdetectors were fabricated into the top plates of digitalmicrofluidics with specially designed ITO working electrodesto allow optical detection and digital microfluidics operation.Ru(Phen)3

2+ was used as ECL label to be intercalated into thedouble strands formed by targets and aptamers on magneticparticles and subsequently measured by this device. Jiang and co-workers developed a kind of homemade screen-printed electro-des chip based aptasensor for simultaneous detection ofmalachite green with chloramphenicol.134 The screen-printedelectrodes chip consisted of two parallel carbon workingelectrodes, an Ag/AgCl reference electrode, and a carboncounter electrode. CdS QDs and luminol-gold nanoparticles (L-Au NPs) labeled ssDNA complementary with two kinds ofaptamers were modified on the two working electrodes as acathode and anode ECL emitters, respectively. Then, ECLquenchers linked aptamers were introduced to electrode surfacesand caused ECL decreases, which would recover in the presenceof targets. Khoshfetrat et al. reported a wireless ECL bipolarelectrode (BPE) array device for the visualized genotyping ofsingle nucleotide polymorphisms (SNPs).135 In the BPE array,signals from each individual anodic pole were controlled by twodriving electrodes, the driving potential was applied through anelectrolyte solution and potential drop in the solution induced apotential difference along the length of the BPE. After thehybridization of targets to the DNA probes modified on theanodic poles of BPE array, genotyping of different SNPs wasmonitored by exposing to different monobase modified luminol-platinum nanoparticles (M-L-PtNPs), which hybridized tomismatch sites and gave ECL emission with the simultaneousO2 reduction at the cathodic poles. Recently, Liu and co-workersdeveloped a paper-based BPE ECL device for genetic detectionof pathogenic bacteria (Figure 4).136 They used wax-screenprinting to form hydrophilic channels on filter paper and screen-printed the carbon ink-based BPE and driving electrodes into thechannels. Then they designed a “light-switch” molecule [Ru-(phen)2dppz]

2+ as ECL reporter. The ECL of this molecule wasquenched by the protonation of the phenazine N atoms inaqueous solution while enhanced after intercalated into the basepairs of dsDNA, which were products from target inducedpolymerase chain reaction (PCR) amplification. Down to 10copies/μL of the genomic DNA of Listeria monocytogenes wasdetected by this device.

ECL Cytosensors. Considering the great contribution toearly stage cancer diagnosis, the cytosensor is another importantapplication field of ECL platforms. Cytosensor is one of the mostrapidly growing class of biosensors. In recent years, ECLmethods are proved to be selective, sensitive, and cost-effectivefor the detection of cancer cells concentration, the distributionstudy of biomolecules on cancer cells surface, the monitoring ofcell apoptosis and even single cell analysis. On the other hand,new developments in nanomaterials and analysis devices haveadvanced the progress of the improvement for ECL cytosensors.Using the ECL nanolabel is a typical strategy in many different

kinds of ECL biosensing platforms including cytosensors. By

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

366

introducing different kinds of functional nanomaterials andaptamers for efficient labels and novel cyto-devices, advancedECL cytosensors keep being developed. For example, Yu et al.reported an origami ECL cyto-device with porous AuPd alloy ascatalytically promoted nanolabels for multiple cancer cellsdetection.137 In this microfluidic paper-based ECL origamicyto-device named as μ-PECLOC, cell-targeting aptamersmodified 3D macroporous Au paper electrodes were used asboth working electrodes and cells capture platforms. As for thenanolabels, they loaded concanavalin-A conjugated porous AuPdalloy nanoparticles (AuPd@Con-A), which could catalyticallypromote the peroxydisulfate ECL system, onto the cancer cellsurface via the specific recognition of cancer cell surface mannosewith Con-A. Excellent analytical performance was achievedtoward the cytosensing of four kinds of cancer cells. Thismicrofluidic paper-based cyto-device or so-called lab-on-paperdevice contributed to the development of facile, portable,disposable, and cost-effective cytosensing platforms. Further-more, they developed a similar microfluidic paper-based cyto-device with GQDs loaded surface villous Au nanocages as ECLnanolabels for in situ determination of CA153 at MCF-7 cellsurface.138 Recently, they further improved the bimetallic AuPdnanoparticles based lab-on-paper cyto-device to detect twoantigens at the MCF-7 cell surface.139

Ratiometric ECL platforms exhibit improved sensitivity,stability, and reproducibility during cell analysis. He et al.developed a reusable and dual-potential responsive ECLplatform for synchronously cytosensing and dynamic evaluationof cell surface N-glycan.83 They used cancer cell recognizedaptamer hybridized with capture DNA for cell capture. Theanodic ECL label Ru(phen)3

2+ were intercalated into the groovesof double-strand DNA.With the presence of target cells, aptamerwould specifically interact with target cells and release thecapture DNA and ECL probes Ru(phen)3

2+. On the other hand,concanavalin A conjugated gold nanoparticle modified graphite-C3N4 (Con A@Au−C3N4) was used as negative ECL label for

cell surface N-glycan recognition owing to the excellent cathodicECL properties of g-C3N4. Meanwhile, electrochemicallyreducedMoS2 nanosheets were chosen as electrode modificationmaterial for signal amplification. In this strategy, the negativesignals fromConA@Au−C3N4 nanoprobes were associated withboth cell concentration andN-glycan expression, and the positiveECL signals from Ru(phen)3

2+ were closely related with the cellscaptured on the electrode. Thus, the dynamic evaluation of theN-glycan expression on the cell surface could be realized withhigh sensitivity and excellent selectivity based on the ratio of ECLintensity from the negative and positive potential signals.Recently, Chen’s group developed a ratiometric ECL cytosensorwith graphite-C3N4 nanosheets and Ag−PAMAM−luminolnanocomposites as ECL labels.80 The ECL-RET effect was alsoused in this system. They prepared the Ag-PAMAM-luminolnanocomposite (Ag-PAMAM-luminol) and functionalized itwith DNA probe to hybridize with the aptamers on magneticmicrobeads. Once the target cells got captured by the aptamers,nanocomposites were released and hybridized on the captureDNA modified g-C3N4 nanosheets coated ITO electrode.Because of the RET effect from g-C3N4 nanosheets to Ag NPs,the ECL signal from g-C3N4 at −1.25 V (vs SCE) decreased andthe ECL signal of luminol at +0.45 V (vs SCE) increased. Theratio of these two signals would change corresponding to thechange of target cell concentration.Other cytosensors based on novel ECL nanolabels have been

reported recently, such as the cytosensor with multibranchedDNA hybridization chain reaction linked CdSe/ZnS quantumdot and gold nanoparticles nanocomposites as ECL labels andthe cytosensor using hemin−graphene−Au nanoparticle ternarycomposite as catalyst for ECL coreactant reduction.31,140

Cell apoptosis detection can be achieved by nanolabel basedECL cytosensors. One of the noteworthy works about ECLcytosensor for cell apoptosis monitoring and efficient drugscreening was reported by Yuan et al.92 This platform usedannexin V modified Ru(dcbpy)3

2+-silica composite NPs as ECLlabels and concanavalin A modified gold NPs as signalamplification material and capture agent. It was successfullyapplied to investigate the efficiency of paclitaxel upon breastcancer cell apoptosis. Recently, Zhu’s group developed an ECLcytosensor for the sensitive detection of cancer cells secretedcaspase-3 activity.141 Caspase-3 is commonly treated as thebiomarker for apoptosis because it is frequently activated duringcancer cell apoptosis process. Ru(bpy)3

2+ doped silica NPs actedas ECL labels with TPrA as coreactant, and the nanocompositesconsisting of MWCNTs and gold NPs acted as electrodemodification material. The biotinylated DEVD-peptides werefurther immobilized on the nanocomposites to capture thestreptavidin-modified ECL labels onto electrode by the specificinteraction between biotin and streptavidin, which would givestrong ECL signal. With the cell secreted caspase-3 specificallycleaving the N-terminus of DEVD, ECL labels were releasedfrom electrode surface and led to the decrease of ECL signal.Thus, this biosensor could achieve effective application formonitoring caspase-3 activity.The insulation from cells and steric hindrance from

biorecognition reactions can cause severe suppression of theECL signal from the electrode surface, providing a simple andclassic method to build label-free ECL cytosensors. In recentyears, novel kinds of multifunctional nanomaterials have beendeveloped to improve the performance of label-free ECLcytosensors.142−144 A good example is the cytosensingapplication of the superparamagnetic functionalized graphene/

Figure 4. Scheme of the paper BPE-ECL molecular switch system. (A)Analysis principle of the paper BPE-ECL molecular switch system. (B)Workflow for the paper BPE-ECL analysis system. Reproduced fromLiu, H.; Zhou, X.; Liu, W.; Yang, X.; Xing, D. Anal. Chem. 2016, 88,10191−10197 (ref 136). Copyright 2016 American Chemical Society.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

367

Fe3O4@Au nanocomposites reported by Wang’s group.145 Thiskind of multifunctional nanocomposites were formed byintegrating poly(ethylenimine) functionalized graphene/ironoxide hybrids (BGNs/Fe3O4) and luminol functionalized goldnanoparticles to give good ECL emission and magnetical controlas well as promote electron transfer. This cytosensor showedgood stability, sensitivity, and reproducibility in HeLa cellsdetermination. Another example is the ECL cytosensor forHepG2 cells reported by Liu et al.146 A novel kind ofnanocomposites consisting of highly oriented CdS-coated ZnOnanorod arrays were developed for electrode modification. Thisnanocomposites arrays had excellent ECL property, goodstability, and fast response speed during detection. They alsoapplied gold nanoparticles onto the nanocomposites arrays forsignal amplification and cell capture antibodies modification.This nanocomposites arrays based label-free ECL cytosensorshowed sensitive response to HepG2 cells in a linear range of300−10 000 cells per mL.Meanwhile, advanced devices have been developed in label-

free ECL cytosensing platforms. Chen’s group developed a visualcolor-switch ECL cytosensor on a multichannel bipolar electrodechip.86 The bipolar electrode (BPE) was developed in theirprevious work of an ECL biosensor for cell surface proteindetection.147 The BPE-ECL platform was built based on amicrochannel chip with a BPE embedded in it. When sufficientlyhigh potential applied through the microchannel chip, reductionand oxidation reactions would occur on the ends of BPE with thesame rate. In this case, the ECL reaction at anode would be highlyinfluenced by the cathodic reduction reaction. In their color-switch ECL cytosensor, the microchannel chip had threeseparated reservoirs with buffer, luminol, Ru(bpy)3

2+/TPrAsolutions, respectively, and two arrays of BPEs. After voltageapplied, the orange ECL emission from Ru(bpy)3

2+/TPrAsystem was observed at the anode of one BPE. By addingH2O2 and DNAzyme, the orange ECL was quenched, while theblue ECL signal from luminol was observed at the anode of theother BPE. With the fact that H2O2 could be produced bystimulating cancer cells, this cytosensor was applied toquantitatively detect HL-60 cancer. Recently, they reportedanother ECL cytosensing platform with bipolar electrodechip.148 The anode of BPE acted as a reporting pole with AuNPs assembled by the DNA double strand. Au NPs worked as acatalyzer for the ECL reaction of the luminol system as well asseeds for the reduction reaction of the Ag layer which couldamplify a slight conductivity change during detection. Alsobecause of the formation of Ag@Au, ECL emission of luminolwould be completely quenched while the ECL recovery couldreflect the extent of anodic dissolution. Down to 5 cells/cm2 ofcancer cells such as MCF-7 and A549 could be quantified due tothe difference of conductivity by monitoring the ECL recoverytime before and after cells incubation.Cellular heterogeneity analysis is a crucial issue in bioanalysis

fields, especially in cancer analysis. It is a central challenge tounderstand how individual cell process and respond to variousinformation. Single cells analysis can give distinct and significantstudy for cellular heterogeneity at high resolution, providingvaluable information such as chemical composition and surfacelocal activities of cells.149 Jiang’s group reported a series of ECLplatforms for single cell monitoring and analysis in recent years.After the investigation of active cholesterol at the single cell levelwith the photomultiplier tube (PMT) based ECL platform,150,151

they further improved their detecting device by building an ECLimaging platform with a charge-coupled device (CCD) to collect

the ECL signal (Figure 5).152 This ECL imaging platform couldcollect the signal from the entire electrode surface, achieving

simultaneous analysis of active membrane cholesterol onmultiple single Hela cells. Furthermore, with this ECL imagingplatform they achieved the visualization of intracellular hydrogenperoxide at the single cell.153 In this system, a comprehensive Au-luminol-microelectrode was developed as the working electrode.This microelectrode was made of a capillary filled with themixture of chitosan and luminol and coated with thin layers ofpolyvinyl chloride/nitrophenyloctyl ether (PVC/NPOE) andgold with a tip opening of 1−2 μm. Thanks to the small diameterof the tip, this microelectrode could be inserted into one signalcell and contact with the intracellular hydrogen peroxide, leadingto ECL emission from the luminol inside the microelectrode tip.Recently, they further studied the intracellular glucose at thesingle cell level using the ECL imaging platform with a goldcoated ITO slide as the working electrode.5 This gold coatedITO slide had cell-sized microwells on the surface to retainindividual cells. Upon treating with luminol, triton X-100, andglucose oxidase, intracellular glucose would be released into themicrowell and generate hydrogen peroxide which were furtherinvolved in the ECL emission of luminol. Large deviations ofglucose concentration from tested single cells were observed,revealing high cellular heterogeneity in intracellular glucose.Their research of this series provides important information oncellular heterogeneity study and give a potential ECL platformfor single cell analysis.

■ CONCLUSIONS AND OUTLOOKSInherent sensitivity, negligible background, simplicity, controll-ability continue to be strong driving forces for the developmentof ECL assays. ECL has established itself as a powerful tool forultrasensitive detection of a wide range of analytes. Multifariousstrategies are used to improve the efficacy of ECL assays. Therehave been hundreds of relevant papers published during the past2 years. These achievements containing new variations of ECLemitters and devices, have widened ECL sensing strategies,advanced the development of high-throughput and portable ECLassays especially immunoassays and genoassays, and even offereda new form of bioimaging method. Some high-throughput ECLimmunoassays have been commercialized such as the Elecsystechnology from Roche154 and the MULTI-ARRAY Technologyfrom Meso Scale Diagnostics.155 These commercialized ECLimmunoassays have high sensitivity, broad dynamic range, andlow background. These systems are easy to use and quicker thanconventional enzyme-linked immunosorbent assay (ELISA).

Figure 5. Schematic illustration of ECL imaging device and ECL imageof parallel single-cell analysis of active membrane cholesterol.Reproduced from Zhou, J.; Ma, G.; Chen, Y.; Fang, D.; Jiang, D.;Chen, H.-Y. Anal. Chem. 2015, 87, 8138−8143 (ref 152). Copyright2015 American Chemical Society.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

368

They can achieve clinical data in a variety of sample types,including serum, plasma, cell supernatant, and even whole blood.However, these commercialized ECL immunoassays are mainlybased on the ECL reaction of the ruthenium-complex and TPrA.Thus, in spite of all the advantages of commercialized ECLimmunoassays, many laboratories find that ELISA offersrelatively inexpensive materials. Fortunately, some of the novelassays with low-cost ECL materials and the paper-based portabledevices mentioned above may give the commercialized ECLtechnology a brilliant future.Despite these burgeoning developments, there are still great

challenges to be addressed in the future. Until now, mostnanoemitters have inferior ECL efficiency to Ru(bpy)3

2+.156,157

Therefore, it is still one of the key subjects in ECL research todevelop innovative, stable, highly efficient, and cost-effectiveECL luminophores. Though multifarious signal amplificationstrategies have been designed, there is still plenty of room for newideas for novel efficient sensing methodologies. The develop-ment of ECL high-throughput point-of-care assays based onmicrofluidic technologies, bipolar electrochemistry, and awireless system to meet the criteria of being ASSURED (i.e.,affordable, sensitive, specific, user-friendly, rapid and robust,equipment-free, and deliverable to end-users) remains asubstantial challenge.On the other hand, current ECL assays mainly based on

potential resolved signal changes by using PMT. Since PMT onlymeasures the global number of photons emitted, a fullyquantitative measurement allowing a deconvolution of ECLcontributions was not possible.158 Besides, in comparison withsmall potential difference between different emitters, thewavelength of most emitters can be easily tuned spanning fromvisible to infrared region. Therefore, wavelength-based ECL mayhold great promise in the development of multivariate analysis.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: jjzhu@nju.edu.cn.ORCIDJun-Jie Zhu: 0000-0002-8201-1285Author Contributions†L.L. and Y.C. contributed equally.NotesThe authors declare no competing financial interest.BiographiesLingling Li received her Ph.D. degree in chemistry from the School ofChemistry and Chemical Engineering, Nanjing University in 2011.Then she did her postdoctoral research in the group of Prof. Jun-Jie Zhuat Nanjing University from 2011 to 2013. Currently she is an associateresearch fellow at Nanjing University. Her research interests focuses onpreparation of novel quantum dots and their applications in electro-chemiluminescence studies.

Ying Chen received her B.S. degree from Nanjing University in 2013.She is currently a Ph.D. candidate with Prof. Jun-Jie Zhu at the School ofChemistry and Chemical Engineering, Nanjing University, China. Herresearch involves multifunctional quantum dots and their applications inelectrochemiluminescence sensing and imaging.

Jun-Jie Zhu received his B.S. (1984) and Ph.D. (1993) degrees from theDepartment of Chemistry, Nanjing University, China. Then, he beganhis academic career at School of Chemistry and Chemical Engineering,Nanjing University. He entered Bar-Ilan University, Israel, as apostdoctoral researcher from 1998 to 1999. Since 2001, he has been a

full professor at the School of Chemistry and Chemical Engineering,Nanjing University. His main research activities focus on preparationand application of functional nanomaterials and fabrication ofelectrochemical and electrochemiluminescence biosensors.

■ ACKNOWLEDGMENTS

We gratefully appreciate the National Natural ScienceFoundation of China (Grants 21427807, 21335004, and21405078).

■ REFERENCES(1) Richter, M. Chem. Rev. 2004, 104, 3003−3036.(2) Miao, W. J. Chem. Rev. 2008, 108, 2506−2553.(3) Swanick, K. N.; Sandroni, M.; Ding, Z.; Zysman-Colman, E. Chem.- Eur. J. 2015, 21, 7435−40.(4) Zhou, Y.; Yan, D.; Wei, M. J. Mater. Chem. C 2015, 3, 10099−10106.(5) Xu, J.; Huang, P.; Qin, Y.; Jiang, D.; Chen, H.-Y. Anal. Chem. 2016,88, 4609−4612.(6) Liu, Z.; Qi, W.; Xu, G. Chem. Soc. Rev. 2015, 44, 3117−3142.(7) Deng, S.; Ju, H. Analyst 2013, 138, 43−61.(8) Nepomnyashchii, A. B.; Cho, S.; Rossky, P. J.; Bard, A. J. J. Am.Chem. Soc. 2010, 132, 17550−17559.(9) Nepomnyashchii, A. B.; Pistner, A. J.; Bard, A. J.; Rosenthal, J. J.Phys. Chem. C 2013, 117, 5599−5609.(10) Dick, J. E.; Poirel, A.; Ziessel, R.; Bard, A. J. Electrochim. Acta 2015,178, 234−239.(11) Hesari, M.; Lu, J.-s.; Wang, S.; Ding, Z. Chem. Commun. 2015, 51,1081−1084.(12) Pinaud, F.; Russo, L.; Pinet, S.; Gosse, I.; Ravaine, V.; Sojic, N. J.Am. Chem. Soc. 2013, 135, 5517−5520.(13) Lu, Q.; Zhang, J.; Wu, Y.; Yuan, R.; Chen, S. RSC Adv. 2015, 5,22289−22293.(14) Zhao, J.; Lei, Y.-M.; Chai, Y.-Q.; Yuan, R.; Zhuo, Y. Biosens.Bioelectron. 2016, 86, 720−727.(15) Price, J. T.; Li, M. S. M.; Brazeau, A. L.; Tao, D.; Xiang, G.; Chen,Y. J. Phys. Chem. C 2016, 120, 21778−21789.(16) Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem. Rev.2001, 101, 3747−3792.(17) Qi, H.; Zhang, C.; Huang, Z.; Wang, L.; Wang, W.; Bard, A. J. J.Am. Chem. Soc. 2016, 138, 1947−1954.(18) Zhou, Y.; Li, W.; Yu, L.; Liu, Y.; Wang, X.; Zhou, M.Dalton Trans.2015, 44, 1858−1865.(19) Fernandez-Hernandez, J. M.; Longhi, E.; Cysewski, R.; Polo, F.;Josel, H.-P.; De Cola, L. Anal. Chem. 2016, 88, 4174−4178.(20) Jiang, Y.; Guo, W.-J.; Kong, D.-X.; Wang, Y.-T.; Wang, J.-Y.; Wei,Q.-H. Dalton Trans. 2015, 44, 3941−3944.(21) Doeven, E. H.; Barbante, G. J.; Kerr, E.; Hogan, C. F.; Endler, J. A.;Francis, P. S. Anal. Chem. 2014, 86, 2727−2732.(22) Doeven, E. H.; Zammit, E. M.; Barbante, G. J.; Francis, P. S.;Barnett, N. W.; Hogan, C. F. Chem. Sci. 2013, 4, 977−982.(23) Kerr, E.; Doeven, E. H.; Barbante, G. J.; Hogan, C. F.; Bower, D. J.;Donnelly, P. S.; Connell, T. U.; Francis, P. S. Chem. Sci. 2015, 6, 472−479.(24) Kerr, E.; Doeven, E. H.; Barbante, G. J.; Hogan, C. F.; Hayne, D.J.; Donnelly, P. S.; Francis, P. S. Chem. Sci. 2016, 7, 5271−5279.(25) Haghighatbin, M. A.; Lo, S.-C.; Burn, P. L.; Hogan, C. F. Chem.Sci. 2016, 7, 6974−6980.(26) Sun, S.; Sun, W.; Mu, D.; Jiang, N.; Peng, X. Chem. Commun.2015, 51, 2529−2531.(27) Jie, G.; Qin, Y.; Meng, Q.; Wang, J. Analyst 2015, 140, 79−82.(28)Wang, L.; Luo, D.; Qin, D.; Shan, D.; Lu, X.Anal. Methods 2015, 7,1395−1400.(29) Stewart, A. J.; O’Reilly, E. J.; Moriarty, R. D.; Bertoncello, P.;Keyes, T. E.; Forster, R. J.; Dennany, L. Electrochim. Acta 2015, 157, 8−14.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

369

(30) Lv, X.; Pang, X.; Li, Y.; Yan, T.; Cao, W.; Du, B.; Wei, Q. ACSAppl. Mater. Interfaces 2015, 7, 867−872.(31) Jie, G.; Jie, G. RSC Adv. 2016, 6, 24780−24785.(32) Zhang, X.; Zhang, B.; Miao, W.; Zou, G. Anal. Chem. 2016, 88,5482−5488.(33) Huan, J.; Liu, Q.; Fei, A.; Qian, J.; Dong, X.; Qiu, B.; Mao, H.;Wang, K. Biosens. Bioelectron. 2015, 73, 221−227.(34) Wang, Y.-L.; Cao, J.-T.; Chen, Y.-H.; Liu, Y.-M. Anal. Methods2016, 8, 5242−5247.(35) Zhang, T.; Zhao, H.; Fan, G.; Li, Y.; Li, L.; Quan, X. Electrochim.Acta 2016, 190, 1150−1158.(36) Xiong, C.; Liang, W.; Wang, H.; Zheng, Y.; Zhuo, Y.; Chai, Y.;Yuan, R. Chem. Commun. 2016, 52, 5589−5592.(37) Chen, A.; Ma, S.; Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem. 2016,88, 3203−3210.(38) Tian, R.; Zhang, S.; Li, M.; Zhou, Y.; Lu, B.; Yan, D.; Wei, M.;Evans, D. G.; Duan, X. Adv. Funct. Mater. 2015, 25, 5006−5015.(39) Xiong, M.; Rong, Q.; Meng, H. M.; Zhang, X. B. Biosens.Bioelectron. 2017, 89, 212−223.(40) Feng, Q.-M.; Shen, Y.-Z.; Li, M.-X.; Zhang, Z.-L.; Zhao, W.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2016, 88, 937−944.(41) Guo, X.; Wu, S.; Duan, N.; Wang, Z. Anal. Bioanal. Chem. 2016,408, 3823−3831.(42) Zhao, L.; Li, J.; Liu, Y.; Wei, Y.; Zhang, J.; Zhang, J.; Xia, Q.;Zhang, Q.; Zhao, W.; Chen, X. Sens. Actuators, B 2016, 232, 484−491.(43) Dai, R.;Wu, F.; Xu, H.; Chi, Y.ACS Appl. Mater. Interfaces 2015, 7,15160−15167.(44) Wang, T.; Wang, D.; Padelford, J. W.; Jiang, J.; Wang, G. J. Am.Chem. Soc. 2016, 138, 6380−6383.(45) Chang, Y.-L.; Palacios, R. E.; Fan, F.-R. F.; Bard, A. J.; Barbara, P.F. J. Am. Chem. Soc. 2008, 130, 8906−8907.(46) Lu, Q.; Zhang, J.; Wu, Y.; Chen, S. RSC Adv. 2015, 5, 63650−63654.(47) Chen, H.; Lu, Q.; Liao, J.; Yuan, R.; Chen, S. Chem. Commun.2016, 52, 7276−7279.(48) Feng, Y.; Dai, C.; Lei, J.; Ju, H.; Cheng, Y. Anal. Chem. 2016, 88,845−850.(49) Xu, Y.; Yin, X.-B.; He, X.-W.; Zhang, Y.-K. Biosens. Bioelectron.2015, 68, 197−203.(50) Xiong, C.-Y.; Wang, H.-J.; Liang, W.-B.; Yuan, Y.-L.; Yuan, R.;Chai, Y.-Q. Chem. - Eur. J. 2015, 21, 9825−9832.(51) Ma, H.; Li, X.; Yan, T.; Li, Y.; Liu, H.; Zhang, Y.; Wu, D.; Du, B.;Wei, Q. ACS Appl. Mater. Interfaces 2016, 8, 10121−10127.(52) Ma, H.; Li, X.; Yan, T.; Li, Y.; Zhang, Y.; Wu, D.; Wei, Q.; Du, B.Biosens. Bioelectron. 2016, 79, 379−385.(53) Zhao, Y.; Wang, Q.; Li, J.; Ma, H.; Zhang, Y.; Wu, D.; Du, B.; Wei,Q. J. Mater. Chem. B 2016, 4, 2963−2971.(54) Pang, X.; Li, J.; Zhao, Y.; Wu, D.; Zhang, Y.; Du, B.; Ma, H.; Wei,Q. ACS Appl. Mater. Interfaces 2015, 7, 19260−19267.(55) Wu, W.; Xiao, H.; Luo, S.; Liu, C.; Tang, Y.; Yang, L. Sens.Actuators, B 2016, 222, 747−754.(56) Jiang, D.; Du, X.; Liu, Q.; Zhou, L.; Qian, J.; Wang, K. ACS Appl.Mater. Interfaces 2015, 7, 3093−3100.(57) Huang, C.; Chen, X.; Lu, Y.; Yang, H.; Yang, W. Biosens.Bioelectron. 2015, 63, 478−482.(58) Chen, L.; Zeng, X.; Ferhan, A. R.; Chi, Y.; Kim, D.-H.; Chen, G.Chem. Commun. 2015, 51, 1035−1038.(59) Zhu, C.; Yang, G.; Li, H.; Du, D.; Lin, Y. Anal. Chem. 2015, 87,230−249.(60) Du, X.; Jiang, D.; Hao, N.; Qian, J.; Dai, L.; Zhou, L.; Hu, J.; Wang,K. Anal. Chem. 2016, 88, 9622−9629.(61) Du, X.; Jiang, D.; Liu, Q.; Qian, J.; Mao, H.; Wang, K. Talanta2015, 132, 146−149.(62) Wu, L.; Wang, J.; Yin, M.; Ren, J.; Miyoshi, D.; Sugimoto, N.; Qu,X. Small 2014, 10, 330−336.(63) Chen, X.; Lian, S.; Ma, Y.; Peng, A.; Tian, X.; Huang, Z.; Chen, X.Talanta 2016, 146, 844−850.(64) Lin, X.; Wang, Q.; Zhu, S.; Xu, J.; Xia, Q.; Fu, Y. RSC Adv. 2016, 6,45829−45834.

(65) Ni, X.; Zhao, Y.; Song, Q. Electrochim. Acta 2015, 164, 31−37.(66) Anjum, S.; Aziz ur, R.; Hu, L.; Majeed, S.; Qi, W.; Zhao, J.; Xu, G.Sens. Actuators, B 2015, 210, 137−143.(67) Xia, H.; Li, L.; Yin, Z.; Hou, X.; Zhu, J.-J. ACS Appl. Mater.Interfaces 2015, 7, 696−703.(68) Chen, L.; Zeng, X.; Si, P.; Chen, Y.; Chi, Y.; Kim, D.-H.; Chen, G.Anal. Chem. 2014, 86, 4188−4195.(69) Dong, Y.-P.; Chen, G.; Zhou, Y.; Zhu, J.-J. Anal. Chem. 2016, 88,1922−1929.(70) Jiang, D.; Zhang, L.; Liu, F.; Liu, C.; Liu, L.; Pu, X. RSC Adv. 2016,6, 19676−19685.(71) Cai, F.; Wang, N.; Dong, T.; Deng, A.; Li, J. Analyst 2015, 140,5885−5890.(72) Zhang, Q.; Xu, G.; Gong, L.; Dai, H.; Zhang, S.; Li, Y.; Lin, Y.Electrochim. Acta 2015, 186, 624−630.(73) Cai, F.; Zhu, Q.; Zhao, K.; Deng, A.; Li, J. Environ. Sci. Technol.2015, 49, 5013−5020.(74) Cheng, Y.; Huang, Y.; Lei, J.; Zhang, L.; Ju, H. Anal. Chem. 2014,86, 5158−5163.(75) Cao, J.-T.; Wang, Y.-L.; Zhang, J.-J.; Zhou, Y.-J.; Ren, S.-W.; Liu,Y.-M. RSC Adv. 2016, 6, 86682−86687.(76) Huang, Y.; Lei, J.; Cheng, Y.; Ju, H. Electrochim. Acta 2015, 155,341−347.(77) Hao, N.; Li, X.-L.; Zhang, H.-R.; Xu, J.-J.; Chen, H.-Y. Chem.Commun. 2014, 50, 14828−14830.(78)Wang, Y.-Z.; Zhao,W.; Dai, P.-P.; Lu, H.-J.; Xu, J.-J.; Pan, J.; Chen,H.-Y. Biosens. Bioelectron. 2016, 86, 683−689.(79) Lei, Y.-M.; Huang, W.-X.; Zhao, M.; Chai, Y.-Q.; Yuan, R.; Zhuo,Y. Anal. Chem. 2015, 87, 7787−7794.(80)Wang, Y.-Z.; Hao, N.; Feng, Q.-M.; Shi, H.-W.; Xu, J.-J.; Chen, H.-Y. Biosens. Bioelectron. 2016, 77, 76−82.(81) Dai, H.; Xu, G.; Zhang, S.; Hong, Z.; Lin, Y.Chem. Commun. 2015,51, 7697−7700.(82) Feng, X.; Gan, N.; Zhang, H.; Li, T.; Cao, Y.; Hu, F.; Jiang, Q.Biosens. Bioelectron. 2016, 75, 308−314.(83) He, Y.; Li, J.; Liu, Y. Anal. Chem. 2015, 87, 9777−9785.(84) Shao, K.; Wang, B.; Ye, S.; Zuo, Y.; Wu, L.; Li, Q.; Lu, Z.; Tan, X.;Han, H. Anal. Chem. 2016, 88, 8179−8187.(85) Zhao, H.-F.; Liang, R.-P.; Wang, J.-W.; Qiu, J.-D. Chem. Commun.2015, 51, 12669−12672.(86) Zhang, H.-R.; Wang, Y.-Z.; Zhao, W.; Xu, J.-J.; Chen, H.-Y. Anal.Chem. 2016, 88, 2884−2890.(87) Wang, H.; He, Y.; Chai, Y.; Yuan, R. Nanoscale 2014, 6, 10316−10322.(88) Wang, H.; Yuan, Y.; Chai, Y.; Yuan, R. Biosens. Bioelectron. 2015,68, 72−77.(89) Jiang, X.; Wang, H.; Wang, H.; Zhuo, Y.; Yuan, R.; Chai, Y.Nanoscale 2016, 8, 8017−8023.(90) Yu, Y.-Q.; Wang, J.-P.; Zhao, M.; Hong, L.-R.; Chai, Y.-Q.; Yuan,R.; Zhuo, Y. Biosens. Bioelectron. 2016, 77, 442−450.(91) Swanick, K. N.; Ladouceur, S.; Zysman-Colman, E.; Ding, Z.Angew. Chem., Int. Ed. 2012, 51, 11079−11082.(92) Liang, W.; Zhuo, Y.; Xiong, C.; Zheng, Y.; Chai, Y.; Yuan, R. Anal.Chem. 2015, 87, 12363−12371.(93) Gui, G.-F.; Zhuo, Y.; Chai, Y.-Q.; Xiang, Y.; Yuan, R. Biosens.Bioelectron. 2016, 77, 7−12.(94)Wang, H.; Yuan, Y.; Zhuo, Y.; Chai, Y.; Yuan, R.Anal. Chem. 2016,88, 5797−5803.(95) Hong, L.-R.; Chai, Y.-Q.; Zhao, M.; Liao, N.; Yuan, R.; Zhuo, Y.Biosens. Bioelectron. 2015, 63, 392−398.(96) Li,M.; Kong, Q.; Bian, Z.;Ma, C.; Ge, S.; Zhang, Y.; Yu, J.; Yan,M.Biosens. Bioelectron. 2015, 65, 176−182.(97) Li, J.; Lu, L.; Kang, T.; Cheng, S. Biosens. Bioelectron. 2016, 77,740−745.(98) Huang, R.-F.; Liu, H.-X.; Gai, Q.-Q.; Liu, G.-J.; Wei, Z. Biosens.Bioelectron. 2015, 71, 194−199.(99) Jiang, X.; Wang, H.; Wang, H.; Yuan, R.; Chai, Y. Anal. Chem.2016, 88, 9243−9250.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

370

(100) Chen, H.; Li, W.; Wang, Q.; Jin, X.; Nie, Z.; Yao, S. Electrochim.Acta 2016, 214, 94−102.(101) Shang, Q.; Zhou, Z.; Shen, Y.; Zhang, Y.; Li, Y.; Liu, S.; Zhang, Y.ACS Appl. Mater. Interfaces 2015, 7, 23672−23678.(102) Yue, X.; Zhu, Z.; Zhang, M.; Ye, Z. Anal. Chem. 2015, 87, 1839−45.(103) Li, H.; Sedgwick, A. C.; Li, M.; Blackburn, R. A.; Bull, S. D.;Arbault, S.; James, T. D.; Sojic, N. Chem. Commun. 2016, 52, 12845−12848.(104) Du, X.; Jiang, D.; Hao, N.; Liu, Q.; Qian, J.; Dai, L.; Mao, H.;Wang, K. Chem. Commun. 2015, 51, 11236−11239.(105) Wang, B.; Wang, H.; Zhong, X.; Chai, Y.; Chen, S.; Yuan, R.Chem. Commun. 2016, 52, 5049−5052.(106) Cao, L.; Zhang, R.; Zhang, W.; Du, Z.; Liu, C.; Ye, Z.; Song, B.;Yuan, J. Biomaterials 2015, 68, 21−31.(107) Taokaenchan, N.; Tangkuaram, T.; Pookmanee, P.;Phaisansuthichol, S.; Kuimalee, S.; Satienperakul, S. Biosens. Bioelectron.2015, 66, 231−237.(108) Miao, Y.-B.; Ren, H.-X.; Gan, N.; Zhou, Y.; Cao, Y.; Li, T.; Chen,Y. Biosens. Bioelectron. 2016, 86, 477−483.(109) Ma, H.; Zhou, J.; Li, Y.; Han, T.; Zhang, Y.; Hu, L.; Du, B.; Wei,Q. Biosens. Bioelectron. 2016, 80, 352−358.(110) Zhang, L.; He, Y.; Wang, H.; Yuan, Y.; Yuan, R.; Chai, Y. Biosens.Bioelectron. 2015, 74, 924−930.(111) Wang, H.; Yuan, Y.; Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem.2016, 88, 2258−2265.(112) Liu, X.; Jiang, H.; Fang, Y.; Zhao, W.; Wang, N.; Zang, G. Anal.Chem. 2015, 87, 9163−9169.(113) Habtamu, H. B.; Sentic, M.; Silvestrini, M.; De Leo, L.; Not, T.;Arbault, S.; Manojlovic, D.; Sojic, N.; Ugo, P. Anal. Chem. 2015, 87,12080−12087.(114) Zhang, H.; Li, M.; Li, C.; Guo, Z.; Dong, H.; Wu, P.; Cai, C.Biosens. Bioelectron. 2015, 74, 98−103.(115) Zhang, P.; Wu, X.; Yuan, R.; Chai, Y. Anal. Chem. 2015, 87,3202−3207.(116) Chen, Y.; Xiang, Y.; Yuan, R.; Chai, Y. Nanoscale 2015, 7, 981−986.(117) Xu, Z.; Dong, Y.; Li, J.; Yuan, R. Chem. Commun. 2015, 51,14369−14372.(118) Liu, W.; Yu, H.; Zhou, X.; Xing, D. Anal. Chem. 2016, 88, 8369−8374.(119) Yang, L.; Tao, Y.; Yue, G.; Li, R.; Qiu, B.; Guo, L.; Lin, Z.; Yang,H.-H. Anal. Chem. 2016, 88, 5097−5103.(120)Huang, X.; Huang, X.; Zhang, A.; Zhuo, B.; Lu, F.; Chen, Y.; Gao,W. Biosens. Bioelectron. 2015, 70, 441−446.(121) Chen, L.; Zeng, X.; Dandapat, A.; Chi, Y.; Kim, D. Anal. Chem.2015, 87, 8851−8857.(122) Lian, W.; Yu, X.; Wang, L.; Liu, H. J. Phys. Chem. C 2015, 119,20003−20010.(123) Liu, S.; Li, M.; Yu, X.; Li, C.-Z.; Liu, H.Chem. Commun. 2015, 51,13185−13188.(124) Lou, J.; Liu, S.; Tu, W.; Dai, Z. Anal. Chem. 2015, 87, 1145−1151.(125)Wang, C.; Qian, J.; Wang, K.; Hua, M.; Liu, Q.; Hao, N.; You, T.;Huang, X. ACS Appl. Mater. Interfaces 2015, 7, 26865−26873.(126)Ma,M.-N.; Zhuo, Y.; Yuan, R.; Chai, Y.-Q. Anal. Chem. 2015, 87,11389−11397.(127) Yu, Y.-Q.; Zhang, H.-Y.; Chai, Y.-Q.; Yuan, R.; Zhuo, Y. Biosens.Bioelectron. 2016, 85, 8−15.(128) Zhou, H.; Han, T.; Wei, Q.; Zhang, S. Anal. Chem. 2016, 88,2976−2983.(129) Wu, D.; Xin, X.; Pang, X.; Pietraszkiewicz, M.; Hozyst, R.; Sun,X. g.; Wei, Q. ACS Appl. Mater. Interfaces 2015, 7, 12663−12670.(130) Zhao, H.-F.; Liang, R.-P.; Wang, J.-W.; Qiu, J.-D. Biosens.Bioelectron. 2015, 63, 458−464.(131) Li, G.; Yu, X.; Liu, D.; Liu, X.; Li, F.; Cui, H. Anal. Chem. 2015,87, 10976−10981.

(132) Wasalathanthri, D. P.; Li, D.; Song, D.; Zheng, Z.; Choudhary,D.; Jansson, I.; Lu, X.; Schenkman, J. B.; Rusling, J. F. Chem. Sci. 2015, 6,2457−2468.(133) Shamsi, M. H.; Choi, K.; Ng, A. H. C.; Dean Chamberlain, M.;Wheeler, A. R. Biosens. Bioelectron. 2016, 77, 845−852.(134) Feng, X.; Gan, N.; Zhang, H.; Yan, Q.; Li, T.; Cao, Y.; Hu, F.; Yu,H.; Jiang, Q. Biosens. Bioelectron. 2015, 74, 587−593.(135) Khoshfetrat, S. M.; Ranjbari, M.; Shayan, M.; Mehrgardi, M. A.;Kiani, A. Anal. Chem. 2015, 87, 8123−8131.(136) Liu, H.; Zhou, X.; Liu, W.; Yang, X.; Xing, D. Anal. Chem. 2016,88, 10191−10197.(137) Wu, L.; Ma, C.; Ge, L.; Kong, Q.; Yan, M.; Ge, S.; Yu, J. Biosens.Bioelectron. 2015, 63, 450−457.(138) Liu, F.; Ge, S.; Su, M.; Song, X.; Yan, M.; Yu, J. Biosens.Bioelectron. 2015, 71, 286−293.(139) Su, M.; Liu, H.; Ge, S.; Ren, N.; Ding, L.; Yu, J.; Song, X. RSCAdv. 2016, 6, 16500−16506.(140) Xin, X.; Yang, Y.; Liu, J.; Wang, X.; Zhou, H.; Yu, B. RSC Adv.2016, 6, 26203−26209.(141) Dong, Y.-P.; Chen, G.; Zhou, Y.; Zhu, J.-J. Anal. Chem. 2016, 88,1922−1929.(142) Wen, Q.; Yang, P.-H. Anal. Methods 2015, 7, 1438−1445.(143) Wu, M.-S.; Sun, X.-T.; Zhu, M.-J.; Chen, H.-Y.; Xu, J.-J. Chem.Commun. 2015, 51, 14072−14075.(144) Dai, B.; Wang, L.; Shao, J.; Huang, X.; Yu, G. RSC Adv. 2016, 6,32874−32880.(145) Gu, W.; Deng, X.; Gu, X.; Jia, X.; Lou, B.; Zhang, X.; Li, J.; Wang,E. Anal. Chem. 2015, 87, 1876−1881.(146) Liu, D.; Wang, L.; Ma, S.; Jiang, Z.; Yang, B.; Han, X.; Liu, S.Nanoscale 2015, 7, 3627−3633.(147) Wu, M.-S.; Yuan, D.-J.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2013,85, 11960−11965.(148) Shi, H.-W.; Zhao, W.; Liu, Z.; Liu, X.-C.; Xu, J.-J.; Chen, H.-Y.Anal. Chem. 2016, 88, 8795−8801.(149) Lawson, D. A.; Bhakta, N. R.; Kessenbrock, K.; Prummel, K. D.;Yu, Y.; Takai, K.; Zhou, A.; Eyob, H.; Balakrishnan, S.; Wang, C.-Y.Nature 2015, 526, 131−135.(150) Ma, G.; Zhou, J.; Tian, C.; Jiang, D.; Fang, D.; Chen, H. Anal.Chem. 2013, 85, 3912−3917.(151) Tian, C.; Zhou, J.; Wu, Z.-Q.; Fang, D.; Jiang, D. Anal. Chem.2014, 86, 678−684.(152) Zhou, J.; Ma, G.; Chen, Y.; Fang, D.; Jiang, D.; Chen, H.-Y. Anal.Chem. 2015, 87, 8138−8143.(153) He, R.; Tang, H.; Jiang, D.; Chen, H.-Y. Anal. Chem. 2016, 88,2006−2009.(154) Roche Diagnostics. Products and Solutions, 2016, http://www.cobas.com/content/dam/cobas_com/pdf/lists/products-and-solutions.pdf.(155) Meso Scale Diagnostics. MULTI-ARRAY Technology, https://www.mesoscale.com/en/technical_resources/our_technology/multi-array.(156) Wang, F.; Lin, J.; Zhao, T.; Hu, D.; Wu, T.; Liu, Y. J. Am. Chem.Soc. 2016, 138, 7718−24.(157) Hesari, M.; Swanick, K. N.; Lu, J.-S.; Whyte, R.; Wang, S.; Ding,Z. J. Am. Chem. Soc. 2015, 137, 11266−11269.(158) de Poulpiquet, A.; Diez-Buitrago, B.; Milutinovic, M. D.; Sentic,M.; Arbault, S.; Bouffier, L.; Kuhn, A.; Sojic, N. Anal. Chem. 2016, 88,6585−6592.

Analytical Chemistry Review

DOI: 10.1021/acs.analchem.6b04675Anal. Chem. 2017, 89, 358−371

371