Electronic Supplementary Information Sensing Properties of … · 2016-09-13 · Electronic...
Transcript of Electronic Supplementary Information Sensing Properties of … · 2016-09-13 · Electronic...
Electronic Supplementary Information
Effect of Lithographically Designed Structures on the Caffeine Sensing Properties of Surface Imprinted Films
Jin Young Parka*
Department of Polymer Science and Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566 Republic of Korea
EXPERIMENTAL
Concave hemisphere-patterned poly(dimethylsiloxane) (PDMS) molds
Highly packed 2-D polystyrene (PS) colloidal arrays (dPS = 750 nm, 2.5 wt% (w/v), Alfa Aesar Co.,
slightly negatively charged) were fabricated using a previously reported floating/transfer method.1
After drying for one day, the array was used as a master mold. For the preparation of the PDMS
replica, the silicone elastomer and curing agent (10:1 wt. ratio, Sylgard 184, Dow Corning Co.) were
vigorously mixed in a beaker. Air bubbles were removed by degassing under vacuum, and the
mixture was carefully poured in the PS colloid-arrayed mold placed in a plastic Petri dish. After
thermal curing at 60 C for 23 h, a PDMS replica with a concave hemispherical structure was
obtained. The sample was then cut to a specific size (2 2 cm2), rinsed with toluene to remove
residual PS colloids, and finally stored in a clean Petri dish.
Convex hemisphere-patterned PDMS molds
For convex hemispherical patterns, the same PS colloidal array on a planar PDMS was used. SU-8 50
negative photoresist (10 L) (MicroChem Corp.) was carefully spin-coated on the array at a speed of
4000 rpm for 60 s; the thickness of the SU-8 film was then controlled by weight pressure ( 90 Pa),
before being continuously photo-cured for 10 min using a UV lamp ( = 370 nm and 36 W, the
distance from the substrate: 3 cm) (DR-301C, DR/Bemi). After demolding and rinsing with toluene to
remove the PS colloids, the concave hemispherical SU-8 pattern was dried at 60 C for 2 h and used
as a secondary master mold (Fig. S1). Then, the PDMS replica with a convex hemispherical structure
was replicated using the same procedure described above.
Electronic Supplementary Material (ESI) for Analyst.This journal is © The Royal Society of Chemistry 2016
Preparation of the molecularly imprinted polymer (MIP) solutions
For the fabrication of the MIP films, methacrylic acid (MAA, Daejung Chemicals & Metals Co.),
ethylene glycol dimethacrylate (EGDMA, Sigma-Aldrich Co.), caffeine (Alfa Aesar Co.), and 2,2′-
azobis(2-methylpropionitrile) (AIBN, Daejung Chemicals & Metals Co.) were used as functional
monomer, cross-linker, template molecule, and photo-initiator, respectively. Various MIP precursor
solutions containing caffeine, MAA, and EGDMA were prepared in dimethylformamide (DMF, Tokyo
Chemical Industry Co.) (Fig. S2(a)). All the solutions (placed in vials) were sonicated for 30 min, and
purged with N2 for 5 min after adding the AIBN. Then, the solutions were irradiated with UV light (
= 370 nm, 36 W) for 30 s to increase their viscosity. The non-imprinted polymer (NIP) precursor
solutions (no caffeine) were prepared using the same procedure. To investigate the sensing
properties, various aqueous solutions (ultra-pure water, 18 M·cm) containing caffeine were
prepared, and analogous chemicals such as xanthine, theophylline, and theobromine (Sigma-Aldrich
Co.) were used to investigate the selectivity of both MIP and NIP films.
Concave and convex hemisphere-patterned MIP (cch- and cvh-MIP) films
The fabrication of all poly(MAA-co-EGDMA) MIP sensors was performed using a previously reported
method.2 For both MIP films, an optimized DMF solution (100 L) containing 0.0625 g of caffeine,
0.54 g of MAA, 5.64 g of EGDMA, and 0.072 g of AIBN, was prepared. The fabrication process of the
two imprinted films was as follows: 5 L of an imprinting solution was carefully dropped on the
structured PDMS molds, and a 9 MHz Au-coated AT-cut quartz crystal (active Au area: 0.196 cm2)
was carefully placed on it under low pressure, to maintain a well-distributed physical contact
between the PDMS and the substrate. Simultaneously, UV-initiated polymerization was carried out
for ~78 min. After demolding, all the MIP films were dried at 60 C for 23 h to remove residual
solvent and complete the polymerization.
Characteristics
For a quantitative analysis of the caffeine rebinding process, the resonant frequency shift during
caffeine sensing was monitored in situ under various conditions (including different caffeine
concentrations, two structured MIP films, and analogous chemicals) using a quartz crystal analyzer
(QCA 922 analytical instrument, Seiko EG&G Co.). Field-emission scanning electron microscopy (FE-
SEM, S-4800, Hitachi, Ltd) was used to investigate the surface topography of the SU-8 replicas and
two structured MIP films. In addition, a non-contact mode of atomic-force microscopy (AFM, NX20,
Park Systems) was used to measure the dimensions of the cch- and cvh-MIP films. Fourier transform
infrared spectroscopy (FT-IR-4100) with attenuated total reflectance (PRO450-S, Jasco), and X-ray
photoelectron spectroscopy (Quantera SXM, ULVAC-PHI) with an Al-Kα X-ray source (15 kV, 25 W,
depth profiling, 2 kV) were used to monitor the removal of imprinted caffeine molecules from the
cch- and cvh-MIP films.
UV curing (10 min)
spin-coated SU-8 filmglass substrate
planar PDMS
PS colloidal array
molding
demolding
removal of PS particles
porous SU-8 template
Fig. S1. Fabrication process of the cch-PDMS mold using colloidal lithography.
Caffeine (g) MAA (g) EGDMA(g) AIBN(g) DMF(L)
C-1 0.0282 0.54 5.64 0.072 100C-2 0.0485 0.54 5.64 0.072 100C-3 0.0555 0.54 5.64 0.072 100C-4 0.0625 0.54 5.64 0.072 100C-5 0.0700 0.54 5.64 0.072 100
C-1
C-2
C-3
C-4
C-5
C-1 C-2 C-3 C-4 C-5
(a)(c)
(b)
(d)
0 10 20 30 40 50 60
-250
-200
-150
-100
-50
0 cvh-MIP
Freq
uenc
y Sh
ift [
Hz]
Time [min]
C-1 C-2 C-3 C-4 C-5
Fig. S2. (a) Summary of various MIP precursor solutions for the poly(MAA-co-EGDMA) films
containing caffeine molecules, (b) photograph of the corresponding spin-coated films and solutions,
(c) SEM images of the cvh-MIP films prepared using PDMS molds with concave hemispherical
patterns and different MIP solutions, and (d) resonant frequency shift as a function of time for the
cvh-MIP films during a sensing period of 60 min. Increasing concentration (C-5 > 70 mg) causes the
aggregation of caffeine in the solution, resulting in a relatively lower frequency shift compared to C-
4. In addition, regardless of the concentration variation of the precursor mixture, the geometry
(diameter and height) of the cvh-MIP films was almost identical.
(a)
(b) cch-MIP
cvh-MIP
Fig. S3. AFM images and line profilometries for the (a) cvh- and (b) cch-MIP films.
3000 2500 2000 1500 1000
Tran
smitt
ance
[a.u
]
Wavenumber [cm-1]
Non-imprinted film
Caffeine imprinted film
Caffeine extracted film
1700 16001654
Fig. S4. FT-IR spectra for the non-imprinted (NIP), caffeine-imprinted MIP, and caffeine-extracted
MIP films. The imprinted planar MIP (or NIP) film was fabricated using a MIP precursor solution
containing 0.0242 g of caffeine, 0.09 g of MAA, 1 g of EGDMA, and 0.041 g of AIBN in 1 mL of DMF.
395 400 405 410
0.5
1.0
1.5
2.0
2.5
3.0
C/S
Binding Energy [eV]
X104
395 400 405 410
0.5
1.0
1.5
2.0
2.5
3.0
X104
C/S
Binding Energy [eV]
(a)
(b)
(c)
395 400 405 410
1
2
3
4
5X104
C/S
Binding Energy [eV]
Sputt
er t
ime
Sputt
er t
ime
Sputt
er t
ime
Fig. S5. XPS spectra for the (a) caffeine-imprinted MIP, and (b, c) caffeine-extracted MIP films (cvh-
MIP film) (3 and 10 h of extraction, respectively).
0 10 20 30 40 50 60 70 800
10
20
30
40
50
Resi
stan
ce C
hang
e [
]
Time [min]
cvh-MIP cch-MIP
Fig. S6. Sensor response for the surface-imprinted cch- and cvh-MIP films fabricated using a 100 L
DMF solution containing 0.0625 g of caffeine, 0.54 g of MAA, 5.64 g of EGDMA, and 0.072 g of AIBN:
resistance variation as a function of time for a 1 mg mL–1 aqueous solution of caffeine during the
caffeine rebinding process.
0 10 20 30 40
-250
-200
-150
-100
-50
0
Freq
uenc
y Sh
ift [
Hz]
Time [min]
0 10 20 30 40
-250
-200
-150
-100
-50
0
Freq
uenc
y Sh
ift [
Hz]
Time [min]
1 mg/mL 10-1 mg/mL 10-2 mg/mL 10-3 mg/mL 10-4 mg/mL 10-5 mg/mL 10-6 mg/mL
0 10 20 30 40 50 60 70
-250
-200
-150
-100
-50
0
Freq
uenc
y Sh
ift [
Hz]
Time [min]
0 10 20 30 40 50 60 70
-250
-200
-150
-100
-50
0
Freq
uenc
y Sh
ift [
Hz]
Time [min]
1 mg/mL 10-1 mg/mL 10-2 mg/mL 10-3 mg/mL 10-4 mg/mL 10-5 mg/mL 10-6 mg/mL
(a)
(c)
(b)
(d)
cch-MIP cvh-MIP
cch-NIP cvh-NIP
Fig. S7. Resonant frequency shift as a function of time for the cch- and cvh-MIP (or NIP) films with
various caffeine concentrations (10–61 mg mL–1 in H2O). The surface-imprinted cch- and cvh-MIP (or
NIP) films were fabricated using a 100 L DMF solution containing 0.54 g of MAA, 5.64 g of EGDMA,
0.072 g of AIBN, and 0.0625 g of caffeine (or no caffeine).
0 10 20 30 40-300
-250
-200
-150
-100
-50
0
Fr
euen
cy S
hift
[Hz
]
Time [min]
Caffeine Theobromine Theophylline Xanthine Three other analogues All chemicals
0 10 20 30 40-300
-250
-200
-150
-100
-50
0
Freu
ency
Shi
ft [
Hz]
Time [min]
Caffeine Theobromine Theophylline Xanthine Three other analogues All chemicals
cch-MIP
cvh-MIP
(a)
(b)
Fig. S8. Resonant frequency shift as a function of time for sensing of various target molecules
(individual caffeine, theobromine, theophylline, and xanthine solutions; mixture of three analogues
(theobromine, theophylline, and xanthine), and mixture of all chemicals (caffeine, theobromine,
theophylline, and xanthine) for the surface-imprinted cch-MIP and cvh-MIP films.
1 (a) J. M. Kim, U. –H. Lee, S. –M. Chang and J. Y. Park, Sens. Actuators B, 2014, 200, 25; (b) J. M. Kim, J. C. Yang and J. Y. Park, Sens. Actuators B, 2015, 206, 50.2 (a) J. C. Yang, H. –K. Shin, S. W. Hong and J. Y. Park, Sens. Actuators B, 2015, 216, 476; (b) J. C. Yang and J. Y. Park, ACS Appl. Mater. Interfaces, 2016, 8, 7381.