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Sensors and Actuators B 131 (2008) 432–438

Trace detection of nitroaromatic compounds with layer-by-layer assembled{SBA/PSS}n/PDDA modified electrode

Ye Liu a, Yanyan Yu a, Qinyan Yang a, Yunhe Qu a, Yueming Liu b,Guoyue Shi a,∗, Litong Jin a

a Department of Chemistry, East China Normal University, 3663 Zhongshan Road(N), Shanghai 200062, PR Chinab Shanghai Key Laboratory of Green Chemistry and Chemical Process, Department of Chemistry, East China Normal University,

3663 Zhongshan Road(N), Shanghai 200062, PR China

Received 19 June 2007; received in revised form 28 November 2007; accepted 3 December 2007Available online 1 February 2008

bstract

The {SBA/PSS}n/PDDA films modified electrode was prepared by layer-by-layer (LBL) assembly with mesoporous SiO2 (SBA), poly(sodium-styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) in this paper. SBA is a large pore-size mesoporous material withighly ordered hexagonally arranged mesochannels and high thermal stability etc. The electrochemical characteristics of the {SBA/PSS}n/PDDAlms have been studied by electrochemical impedance spectroscopy in 0.1 M KCl solution containing 5.0 mM Fe(CN)6

3−/Fe(CN)64− at the formal

otential of 0.230 V. The ultratrace nitroaromatic compounds (NACs) such as TNT, TNB, DNT and DNB were determined by differential pulseoltammetry (DPV) measurement. The sensitivities for NACs determination with {SBA/PSS}n/PDDA modified electrode were dependent on the

umber of layers, pH and ionic strength of electrolyte, based on which a set of optimized conditions for film fabrication was inferred. The currentesponses were linear with NACs ranging from 10−9 to 10−7 mol/l. The results showed that the {SBA/PSS}n/PDDA modified electrode establishednew way for fast, simple and sensitive analysis of NACs.2007 Elsevier B.V. All rights reserved.

eywords: {SBA/PSS}n/PDDA; NACs; Detection

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. Introduction

Since the World War II, long-term manufacturing of explo-ives and cumulative use of land and marine firing ranges, asell as military conflicts, have all resulted in severe contami-ation from unexplored ordnance and mines worldwide [1–4].he nitro aromatic compounds (NACs) in explosive, such as,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), 2,4-initrotoluene (DNT) and 1,3-dinitrobenzene (DNB), are toxicnd cause health problems in both animals and human beings,ncluding anemia, abnormal liver function, cataract development

nd skin irritation [5]. Even after degradations, the by-productsf the common explosives in environment are still toxic andarcinogenic [6,7]. Therefore, environmental applications have

∗ Corresponding author. Tel.: +86 21 62237105; fax: +86 21 62232627.E-mail address: gyshi@chem.ecnu.edu.cn (G. Shi).

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925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2007.12.016

enerated great demands for fast detection of nitroaromaticompounds (NACs) [8,9]. The detection of traces of explosiveaterials is of utmost importance and there is a necessity for

ccurate, sensitive, rapid, easy-to-use and portable method toacilitate the detection, quantification and remediation of theseACs.

The widely used methods of detecting trace NACs in vaporr solution include fluorescence [10], immunochemical [11],uminescence [12] and electrochemical voltammetry [13]. Forxample, Altstein et al. [11] used a highly sensitive immuno-hemical method for immunoaffinity purification (IAP) andetection of trace amounts of TNT in a ceramic matrix (sol–gel).oldman et al. [8] demonstrated the use of luminescent quan-

um dots (QDs) conjugated to antibody fragments to develop

olution-phase nanoscale sensing assemblies, based on fluo-escence resonance energy transfer (FRET) for the specificetection of the explosive 2,4,6-trinitrotoluene in aqueous envi-onments. Of these methods, electrochemical voltammetry has

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Y. Liu et al. / Sensors and A

ts particular advantages. The device based on electrochemi-al voltammetry is convenient, fast and can detect the targetompounds directly.

Mesoporous materials, because of their ordered arrays andniform nanochannels, have been widely used in variety ofelds as catalysis, separation, adsorption, etc. [14]. SBA-5 is the largest pore-size mesoporous material with highlyrdered hexagonally arranged mesochannels, with thick walls,djustable pore size from 3 to 30 nm, and high hydrothermalnd thermal stability [15–20]. Compared with other modifiedensors, the SBA-15 modified electrochemical sensor greatlynlarges the chemical surface area available of the workinglectrode and further enables the adsorption ability, making theensitive down to nanomolar level.

Layer-by-layer assembly is a polymer thin film depositionechnique developed by Decher and Hong [21,24] and Rub-er and co-workers [22,23]. Alternately, dipping a substrateetween a polycation and a polyanion solution results in lin-ar film growth with the ultimate thickness being controlled byhe number of bilayers deposited. To modify the glassy carbonlectrode, instead of the traditional method of placing a drop onhe surface of the electrode, method of self-assembled layer-by-ayer films possesses several superiorities over others. First, the

odified layers are combined by static attraction so that theirombination is much firmer and always remains stable duringhe experiment. Second, each of the modified layer films is a

onolayer which is characterized of regular texture, large sur-ace area of the working electrode and particular pore sizes. Atast, the thickness of the films is controllable with the optimalondition.

We report here a successful construction of {SBA/SS}n/PDDA modified glassy carbon electrode with control-

able layers. By means of the layer-by-layer (LBL) technique,SBA/PSS}n/PDDA GCE for the NACs determination was pre-ared by assembling nanometer-sized SBA-15 and PDDA, PSSn the surface of glassy carbon (GC) electrode. The filmsere characterized with scanning electron microscopy (SEM),

ransmission electron microscopy (TEM) and electrochemicalethods including impedance, differential pulse voltammetry

DPV) and cyclic voltammetry (CV). Fast response time, wideinear range and excellent stability were achieved for the detec-ion of NACs by {SBA/PSS}n/PDDA modified electrode. Its a fast, simple and sensitive method and will have widepplication in national security and environmental monitor-ng.

. Experimental

.1. Reagents and solutions

2,4,6-Trinitrotoluene (1000 �g/ml in acetonitrile), 1,3,5trinitrobenzene, 2,4-dinitrotoluene (2,4-DNT), 1,3-initrobenzene (1,3-DNB), poly(diallyldimethylammonium

hloride) (PDDA) and poly(sodium 4-styrene-sulfonate) (PSS)ere all purchased from Sigma–Aldrich Chemical Co. Ltd.,SA. Mesopours SiO2 of SBA-15 were obtained from Shanghaiey Laboratory of Green Chemistry. The solids of NACs of

dit

ors B 131 (2008) 432–438 433

NB, 2,4-DNT, and 1,3-DNB were dissolved in acetonitrile toorm a 1 g/l solution. PDDA and PSS were dissolved in PBSpH 4.0) to form 5 and 20 g/l solutions, respectively. One gramer liter SBA solution was prepared by dispersing SBA in HClolution (pH 1.0) and sonicated for 5 min. Both the 0.1 M KClolution and phosphate buffer solution (PBS), which serveds the supporting electrolyte during the experiments, wererepared with double-distilled water. All reagents were usedithout any further purification

.2. Apparatus

Electrochemical experiments were carried out on a CHI60 A electrochemical workstation (CH Instruments, USA)ith a bare GCE (diameter 3 mm, BAS Co., Japan) or aSBA/PSS}n/PDDA modified electrode as the working elec-rode, a Ag/AgCl (saturated KCl) as the reference electrodend a platinum electrode as the auxiliary electrode. All electro-hemical experiments were performed in a 5 ml voltammetricell at room temperature (25 ◦C ± 1). All solutions were deoxy-enated by bubbling with highly pure nitrogen for at least 20 minnd maintained under nitrogen atmosphere during the measure-ents.

.3. The synthesis of SBA

Fiber-like mesoporous SBA-15 can be synthesized overrange of reaction mixture compositions and condi-

ions. In our work, we followed the previously methodsing tetramethyl orthosilicate (TMOS) as a silica sourcend poly(ethylene oxide)-block-poly(propylene oxide)-block-oly(ethylene oxide) triblock copolymer (Aldrich, Mavg = 5800,O20PO70EO20, P123) as the structure-directing agent.wo grams amphiphilic triblock copolymer, poly(ethylenelycol)-block-poly(propylene glycol)-block-poly(ethylene gly-ol) (average molecular weight 5800, Aldrich), was dispersed in5 g of water and 60 g of 2 M HCl solution with stirring, followedy the addition of 4.25 g of tetraethyl orthosilicate (Aldrich) tohe homogeneous solution with stirring. This gel mixture wasontinuously stirred at 40 ◦C for 24 h and finally crystallized inTeflon-lined autoclave at 100 ◦C for 2 days. After crystalliza-

ion, the solid product was centrifuged, filtered and washed withater. The material was dried in air at room temperature and then

alcined in static air at 550 ◦C for 24 h to decompose the triblockopolymer and obtain a white powder (SBA-15) [15–18].

.4. Fabrication of {SBA/PSS}n/PDDA modified electrode

Before the electrochemical experiments, glassy carbon elec-rode (CH Instrument, diameter = 3 mm) was polished carefullyo a mirror like surface with 0.3- and 0.05-�m alumina slurry andequentially sonicated for 5 min in 1:1nitric acid, 1 M NaOH,cetone and double-distilled water, respectively.

The {SBA/PSS}n/PDDA films were deposited onto the clean,ry GCE following a layer-by-layer deposition strategy shownn Scheme 1. First, the clean GC electrode was soaked intohe aqueous solution of PDDA for 20 min to deposit a pos-

434 Y. Liu et al. / Sensors and Actuat

Scheme 1. The diagram of constructing the {SBA/PSS}n PDDA films on GCe

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tively charged precursor layer of PDDA, and washed andried in the vacuum-oven at 318 K for about 20 min. Second,he PDDA electrode was soaked into PSS solution for about0 min to adsorb the negatively charged PSS through electro-tatic interactions and dried in the vacuum-oven. Third, the SBAlm was formed on the PSS/PDDA by the same way. Beforevery drying, the modified electrode was flushed by double-istilled water to make sure that each of the modified films isonolayer. After these procedures, a SBA/PSS/PDDA film was

abricated. The second and third steps can be repeated for sev-ral times to obtain the desired number of {SBA/PSS}n/PDDAlms.

SBA was characterized by scanning electron microscopyHITACHI S-4700), transmission electron microscopy (JEM-010 electron microscope) and X-ray diffraction (XRD, Bruker8 Advance diffractometer using CuK� radiation).

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Fig. 1. SEM image (A) and TEM images of side

ors B 131 (2008) 432–438

.5. Electrochemical experiments

The electrochemical impedance experiments were performedn the presence of 5.0 mM K3[Fe(CN)6]/K4[Fe(CN)6] in 0.1 MCl with the formal potential of 0.230 V and the frequency from.0001 to 100 KHz. The layers of {SBA/PSS}n were optimizedy electrochemical impedance.{SBA/PSS}n/PDDA films modified electrode as the work-

ng electrode, DPV measurement was performed to optimizehe experimental conditions and determine the NACs with theotential of scan range from 0.1 to −1.0 V, amplitude of 50 mV,ulse width of 0.05 s, sampling width of 0.0167 and pulse periodf 0.2 s. Various volumes of 1 g/l NACs solutions preparedith acetonitrile were added in 0.1 M KCl to obtain differ-

nt concentrations of NACs solutions. The DPV responses ofACs were recorded and the linear ranges and the detection

imits of TNT, TNB, DNT and DNB were also shown in thisaper.

. Result and discussion

.1. Morphology of the SBA

The morphology of the {SBA/PSS}n/PDDA films on elec-rode was obtained by SEM and TEM in Fig. 1. Fig. 1A displayshe side view image of the material, evidently showing that theample consists of many fiber-like domains, which are run-

ing parallel to the long axis and aggregate into wheat-likeacrostructures. The size of the fiber-like particles is relative

niform with 350–400 nm in width, which is the typical size ofhe SBA-15 material. The comparison study of SBA after syn-

(B) and top views (C) of mesoporous SBA.

ctuators B 131 (2008) 432–438 435

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Y. Liu et al. / Sensors and A

hesis and before assembly of the multilayer was also done ande found that little difference was found (figure not shown). So

he properties of SBA were not changed and it can be selecteds a modified materials.

The {SBA/PSS}n/PDDA films were further characterized byEM to observe the mesoporous structures. Fig. 1B and C are

he side and top views of TEM images of SBA, indicating thathe nanorods have parallel-arranged and well-ordered channels,ith a periodic spacing of ∼9 nm, which is bigger than the sizef the NACs molecules, such as TNT (3.1 A × 8.8 A × 8.8 A)nd TNB (3.3 A × 8.8 A × 9.3 A) [26]. Consequently, the NACsolecules can go inside the pore and can be absorbed on the

urface of the SBA material, which is advantageous for thereconcentration and determination of trace NACs.

.2. Electrochemical behavior of {SBA/PSS}n/PDDA/GC

Fig. 2A and B are the DPV responses of bare glassy car-on electrode and {SBA/PSS}n/PDDA modified electrode in5.2 nM and 1.0 �M TNT solutions, respectively. As shownn Fig. 2A, it shows that both the bare and modified glassyarbon electrode display obvious responses at the concentra-ion of 1.0 �M TNT at around −0.78 V, which is derivedrom the reduction of nitro aromatic to hydroxyl amine andhen to amine groups. However the reduction response ofSBA/PSS}n/PDDA/GC is two times of that of bare GC. Fur-hermore, it is reported that the reduction of each nitro aromaticsn NACs is able to generate a redox signal; we only got one in thisork. It might be due to the high background current of the sub-

trates [27]. Fig. 2B shows the DPV responses at bare electrodend {SBA/PSS}3/PDDA modified electrode to TNT with lowoncentration of 35.2 nM. We can hardly see any current changet the potential of −0.78 V to 35.2 nM TNT at bare electrode. Buthe {SBA/PSS}3/PDDA electrode still displays a well voltam-

etric signal for 35.2 nM TNT at −0.78 V. So we can concludehat TNT can be reduced on both the {SBA/PSS}3/PDDA/GC

odified electrode and the bare electrode, but TNT has more sen-itive response at {SBA/PSS}3/PDDA/GC electrode than that atare electrode, especially to the ultratrace NACs.

Therefore, we may attribute the improvement of theSBA/PSS}3/PDDA/GC to ultratrace NACs to the much largerffective surface area available of SBA and further enables thereconcentration of NACs.

.3. Impedance of the modified electrode

The impedance of modified electrodes with different num-ers of SBA/PSS bilayer was scanned in 0.1 M KCl solutionontaining 5.0 mM Fe(CN)6

3−/Fe(CN)64− at the formal poten-

ial of 0.230 V. Fig. 3A shows that the charge transfer resistanceRct) of the {SBA/PSS}n rises with the bilayer numbers(n)rom 1 to 5, depicting that the electron transfer resistance isurther improved with the number of bilayers, which slows

own the electron transfer of the probe due to the electro-tatic repulsion between the positively charged SBA-15 and thee(CN)6

3−/Fe(CN)64−. Fig. 3B shows that in a single layer of

DDA/PSS/SBA, the impedance also increases obviously at a

3

b

DDA/GC electrodes. (A) DPV of bare GC (a) and {SBA/PSS}n PDDA/GC(b)lectrodes in 1.0 �M TNT solution. (B) DPV of bare GC (c) and {SBA/PSS}n

DDA/GC (d) electrodes in 35.2 nM TNT solution.

ange of PDDA, PDDA/PSS, PDDA/PSS/SBA. Both Fig. 3And B show that the thicker the film is, the modified electrode hashe larger obstruction effect [25]. It confirms that the SBA/PSSilayers have been immobilized on the surface of the glassylectrode successfully.

.4. Effect of experimental parameters

Electrodes modified with different number of SBA/PSSilayers display different performances for the measurement

436 Y. Liu et al. / Sensors and Actuators B 131 (2008) 432–438

Fig. 3. Nyquist Plots for the electrochemical impedance measurem-ents at the electrodes of (A) {SBA/PSS}1/PDDAGC(1), :{SBA/PSS}2/PDDA/GC(2),:{SBA/PSS}3/PDDA/GC(3), {SBA/PSS}4/PDDA/GC(4), {SBA/PSS}5PDDA/GC(5). (B) PDDA/GC(1), PSS/PDDA/GC(2),S

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tithe range from 0.1 to 1.0 M of KCl solutions. So 0.1 M KClsolution was selected as the optimum electrolyte in this paper.

BA/PSS/PDDA/GC(3).

f NACs. The {SBA/PSS}3/PDDA modified electrode dis-lays the largest response current at the concentration of 88 nMNT solution, while the responses of {SBA/PSS}1/PDDA/GCnd {SBA/PSS}5/PDDA/GC are just 50% and 67% of thatf {SBA/PSS}3/PDDA/GC for the same TNT concentration.e predict that with the number of the bilayers increasing

rom 1 to 5, the amount of SBA-15 modified on the elec-rode is also increasing which provides larger effective surfacerea and further enables the preconcentration ability of NACsn {SBA/PSS}n/PDDA/GC. We also found that the back-rounds of the {SBA/PSS}5/PDDA films were not stable inhis work (figures not shown). It maybe because the super-

uous films would brush off from the surface of electrodend led to the poor reproducibility and sensitivity for theACs determination at {SBA/PSS}5/PDDA films. Therefore,

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ig. 4. Effect of pH on the responses for 88 nM TNT at {SBA/PSS}3/PDDA/GClectrode.

e choose {SBA/PSS}3 as the optimum films in our experi-ents.Fig. 4 examines the effect of the pH upon the DPV response.

he peak current performs the maximum response with the pHver the 2.0–7.0 range, and then it starts to decrease sharplyn the pH range of 7.0–10.0. It maybe because there is enoughydronium for TNT to form H-bonding with SBA in acidic andeutral electrolyte, but there is less in alkalescence electrolyte19]. Hence, neutral electrolyte was selected as the optimum pHalue of electrolyte.

We also studied the dependence of the DPV responses uponhe ionic strength of electrolyte. The {SBA/PSS}3/PDDA mod-fied electrode shows nearly ionic strength independence over

ig. 5. The DPV responses for the solutions of a, base; b, 4.4 nM; c, 8.8 nM; d,7.6 nM; e, 35.2 nM; f, 44.0 nM; g, 61.6 Nm; h, 88.0 nM and I, 220.0 nM TNTt {SBA/PSS}3/PDDA/GC modified electrode.

Y. Liu et al. / Sensors and Actuators B 131 (2008) 432–438 437

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.5. Stability and reproducibility of the {SBA/PSS}3/PDDAlectrode

The electrocatalytic activity of {SBA/PSS}3/PDDA mod-fied electrode was tested in 5.0 × 10−8 M TNT for siximes each day for continuous 4 days, the RSD of the cur-ent respond is 2.1%. After 2 weeks, the sensor retains0% of initial current respond to the 5.0 × 10−8 M TNT. Inddition, the modified electrode also showed a good repro-ucibility. The five electrodes fabricated independently, showedn acceptable reproducibility in the current response to the.0 × 10−8 M TNT with a R.S.D. of 5.6%. These results showhat {SBA/PSS}3/PDDA modified electrode are very stable for

easurement of NACs.

.6. Detection of TNT, TNB, DNT, DNB

Fig. 5 shows the DPV response of the TNT from 4.4 to 220 nMb–i) at {SBA/PSS}3/PDDA modified electrode, alone with thelank voltammogram (a). As the increase of the TNT concen-ration, a continually increasing of reduction current can be seen

t the potential of −0.78 V around.

The calibration curves of the detection of NACs were allhown in Fig. 6. It is found that highly linear range can bechieved to NACs at {SBA/PSS}3/PDDA/GC electrode. The

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dified electrode. (A) TNT, (B) TNB, (C) DNT and (D) DNB.

etection limits of the four nitroaromatic compounds TNT, TNB,NT, DNB are 2.0 × 10−9, 2.0 × 10−9, 1.5 × 10−9, 2.0 × 10−9,

espectively.

. Conclusion

A {SBA/PSS}3/PDDA electrode for the measurement of thexplosive NACs has been demonstrated in this paper. The SBAxhibits large surface area, significantly narrower channel andarge pore volume which help to the NACs’ preconcentration and

easurement. It shows that the {SBA/PSS}3/PDDA electrodeas high sensitivity and good stability for the electrocatalyticaleductive of NACs. The proposed electrochemical sensing tech-ology is thus to open new opportunities for detecting NACsnd is undoubtedly of great promising for the development ofiniaturized and field-portable detection kits, which we hope to

emonstrate in the near future.

cknowledgements

This work is supported by the National Natural Science Foun-

ation of China (no. 20675032), Program for New Centuryxcellent Talents in University (NCET-07-0293), the Nationalasic Research Program of China (no. 2006CB202508) andhanghai Rising-Star program (06QH14004).

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eferences

[1] R.F. Spaulding, J.W. Fulton, J. Contam. Hydrol. 2 (1988) 139–153.[2] P.Y. Charles, B.M. Dingle, S. Van Bergen, P.R. Gauger, C.H. Patterson,

A.W. Kusterbeck, Field Anal. Chem. Technol. 5 (2001) 272–280.[3] R. Boopathy, J. Manning, C. Montemagno, K. Rimkus, Can. J. Microbiol.

40 (1994) 787–790.[4] M.R. Darrach, A. Chutjian, G.A. Plett, Environ. Sci. Technol. 32 (1998)

1354–1358.[5] G.P. Anderson, S.C. Moreira, P.T. Charles, I.L. Medintz, E.R. Goldman,

M. Zeinali, C.R. Taitt, Anal. Chem. 78 (7) (2006) 2279–2285.[6] W.D. Won, L.H. Disalvo, J. NG, Appl. Environ. Microbiol. 31 (1976)

576–580.[7] S. Homma-Takeda, Y. Hiraku, Y. Ohkama, Free Radic. Res. 36 (2002)

555–566.[8] E.R. Goldman, T.J. Cohill, C.H. Patterson Jr., G.P. Anderson, A.W. Kuster-

beck, J.M. Mauro, Environ. Sci. Technol. 37 (20) (2003) 4733–4736.[9] J. Yinon, Anal. Chem. 75 (5) (2003) 98A–105A.10] Y. Liu, R.C. Mills, J.M. Boncella, K.S. Schanze, Langmuir 17 (24) (2001)

7452–7455.11] M. Altstein, A. Bronshtein, B. Glattstein, A. Zeichner, T. Tamiri, J. Almog,

Anal. Chem. 73 (11) (2001) 2461–2467.12] H. Sohn, M.J. Sailor, D. Magde, W.C. Trogler, J. Am. Chem. Soc. 125 (13)

(2003) 3821–3830.13] J. Wang, S.B. Hocevar, B. Ogorevc, Electrochem. Commun. 6 (2004)

176.14] H. Zhang, J.M. Sun, D. Ma, X.H. Bao, A.K. Hoffmann, G. Weinberg, D.S.

Su, R. Schlo, J. Am. Chem. Soc. 126 (2004) 7440–7441.15] D.Y. Zhao, J.P. Feng, Q.S. Huo, N. Melosh, G.H. Fredrickson, B.F.

Chmelka, G.D. Stucky, Science 279 (1998) 348.16] D.Y. Zhao, Q.S. Huo, J.P. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem.

Soc. 120 (1998) 6024–6036.17] D.Y. Zhao, J.Y. Sun, Q.Z. Li, G.D. Stucky, Chem. Mater. 12 (2000)

275–279.18] Z.H. Luan, M. Hartmann, D.Y. Zhao, W.Z. Zhou, L. Kevan, Chem. Mater.

11 (1999) 1621–1627.19] B.L. Newalkar, S. Komarneni, H. Katsuki, Chem. Commun. (2000) 2389.20] S. Madhugiri, A. Dalton, J. Gutierrez, J.P. Ferraris, K.J. Balkus, J. Am.

Chem. Soc. 125 (2003) 14531–14538.21] G. Decher, J.D. Hong, Makromol. Chem. Macromol. Symp. 46 (1991)

321.22] M. Ferriera, J.H. Cheung, M.F. Rubner, Thin Solid Films 244 (1994) 806.23] A.C. Fou, M.F. Rubner, Macromolecules 28 (1995) 7115–7120.24] G. Decher, Science 277 (1997) 1232.25] G.K. Vasilyeva, V.D. Kreslavski, P.J. Shea, Chemosphere 47 (2002) 311.

NfvHr

ors B 131 (2008) 432–438

26] J.J. Feng, J.J. Xu, H.Y. Chen, Biosens. Bioelectron. 22 (2007) 1618–1624.27] J. Wang, R.K. Bhada, J.M. Lu, D. MacDonald, Anal. Chim. Acta 361 (1998)

85.

iographies

e Liu is currently a graduate student in Department of Chemistry, East Chinaormal University. She received her bachelor degree in chemistry (2006) fromast China Normal University in Shanghai, China. Her research interest is mainly

n electrochemistry and sensors.

anyan Yu is currently a graduate student in Department of Chemistry, Easthina Normal University. She received her bachelor degree in chemistry (2007)

rom Huaibei Coal Industry Teachers’ College in Anhui, China. Her researchnterest is mainly in electrochemistry and sensors.

inyan Yang is currently a graduate student in Department of Chemistry, Easthina Normal University. She received her bachelor degree in chemistry (2007)

rom East China Normal University in Shanghai, China. Her research interest isainly in electrochemistry and sensors.

unhe Qu is currently a graduate student in Department of Chemistry, Easthina Normal University. He received his bachelor degree in applied chemistry

2005) from East China Normal University in Shanghai, China. His researchnterest is mainly in electrochemistry and sensors.

ueming Liu is an associate professor of chemistry in Department of Chem-stry, East China Normal University in Shanghai, China. He received his BScn organic chemistry (1994) from Dalian University of Technology. He is a fac-lty member of Shanghai Key Laboratory of Green Chemistry and Chemicalrocesses. His research interests cover zeolite catalysts and material.

uoyue Shi is a professor of chemistry in Department of Chemistry, East Chinaormal University (ECNU) in Shanghai, China. He received his PhD in chem-

stry (1999) from ECNU. He acted as an advanced visiting scholar in Laboratoryf Research and Development, BAS Inc., Tokyo, Japan from January2002 toanuary 2003 and had a postdoc position in chemistry of University of Pitts-urgh, PA, USA from March 2003 to May 2005. Now he is a faculty memberf Department of Chemistry in ECNU. His research interests cover bio-sensorsnd analytical chemistry.

itong Jin is a professor of chemistry in Department of Chemistry, East China

ormal University in Shanghai, China. He received his BSc in chemistry (1960)

rom East China Normal University. During 1982–1985, he acted as an advancedisiting scholar in Department of Chemistry, Nagoya University, Nagoya, Japan.e is a faculty member of Department of Chemistry in this university. His

esearch interests cover bio-electrochemistry and sensors