Synthesis of CdS quantum dots decorated graphene nanosheets and non-enzymatic photoelectrochemical detection of glucose

Accepted Manuscript Title: Synthesis of CdS quantum dots decorated graphene nanosheets and non-enzymatic photoelectrochemical detection of glucose Author: Xuyan Zhang Fang Xu Bingqing Zhao Xin Ji Yanwen Yao Dapeng Wu Zhiyong Gao Kai Jiang PII: DOI: Reference:

S0013-4686(14)00836-6 http://dx.doi.org/doi:10.1016/j.electacta.2014.04.089 EA 22595

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

5-12-2013 14-4-2014 15-4-2014

Please cite this article as: X. Zhang, F. Xu, B. Zhao, X. Ji, Y. Yao, D. Wu, Z. Gao, K. Jiang, Synthesis of CdS quantum dots decorated graphene nanosheets and nonenzymatic photoelectrochemical detection of glucose, Electrochimica Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.04.089 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis of CdS quantum dots decorated graphene nanosheets and nonenzymatic photoelectrochemical detection of glucose Xuyan Zhanga, Fang Xua*, Bingqing Zhaoa, Xin Jia, Yanwen Yao1, Dapeng Wua, b,

School of Chemistry and Chemical Engineering, Henan Normal University,

cr

a

ip t

Zhiyong Gaoa, b, Kai Jianga, b*

us

Xinxiang, Henan 453007, PR China Tel. /Fax: +86 373 3326336; E-mail address: [email protected] (F. Xu)

Engineering Technology Research Center of Motive Power and Key Materials of

an

b

Henan Province, Henan Normal University, Xinxiang, Henan 453007, PR China Tel.

M

/Fax: +86 373 3326209; E-mail address: [email protected] (K. Jiang) ABSTRACT：

te

d

Graphene-CdS quantum dots (QDs) hybrid materials were successfully prepared via one-step hydrothermal method. CdS QDs with average size of ~6 nm were

Ac ce p

dispersed on graphene sheets with high coverage through non-covalent bonding. Photocurrent and electrochemical impedance spectroscopy (EIS) results suggested that the best dosage of graphene oxide for graphene-CdS hybrid materials is 0.5% (G0.5-CdS). When G0.5-CdS QDs was used as photoanode materials in nonenzymatic sensor, and the sensor was used to detect glucose and displayed satisfactory analytical performance with good linear range from 0.1~4 mmol dm-3 with a detection limit of 7 μmol dm-3 at a signal-to-noise ratio of 3. The sensor also possessed high

selectivity and durability in trace detection of glucose. Keywords:

Graphene-CdS

hybrid

material,

hydrothermal

method,

Page 1 of 30

photoelectrochemical sensor, glucose detection 1. Introduction Quantum dots (QDs)-based sensor for chemical and biological detection is

ip t

presently a technological hot topic because of the following advantages: (1) fast

cr

response and high sensitivity; (2) small dark current; (3) versatility for spatially

us

resolved coding or multichannel detection [1]. Although QDs helps to chemically coupled to additional moieties, such as biomolecules, they are not stable and prone to

an

aggregate due to large active surface area, which results in deteriorations of photoelectrochemical properties. Numerous hybrids of QDs with semiconductors or

M

metals [2-7], have been developed to overcome these limitations, resulting in high

te

efficiency.

d

efficient separation of electron-hole pairs and photoelectrochemical (PEC) conversion

It is well known that graphene, a two dimensional carbon nanomaterial, has a

Ac ce p

great potential for developing graphene-based hybrids as a nanoscale building block due to its high specific surface area, zero band gap and high electron mobility [8, 9]. The graphene-QDs composites not only take advantages of the superior properties of graphene and QDs, but also lead to some special novel properties through the combination of graphene with QDs. Many graphene-QDs, including graphene-V2O5, graphene-ZnS, graphene-ZnO, and graphene-CdS have been used in lithium batteries, photocatalytic degradation organic dyes, gas sensing et al. [10-13]. Of particularly interest are graphene-CdS QDs hybrid materials, which have aroused extensive interest for potential photocatalytic, electrochemical, and optoelectronic applications

Page 2 of 30

[14-16]. Compared with bare CdS QDs, graphene-CdS hybrid materials have fast and efficient electron-transfer from CdS QDs to graphene, which can lead to distinct increment of photocurrent. Recently, the graphene-CdS nanocomposites have been

ip t

applied as photoelectrochemical (PEC) sensor for detection of environmental

cr

pollutants and biomolecules [17-19] due to its high sensitivity via combining the

us

advantages of optical and electrochemical sensors. Graphene-CdS QDs with good crystalline structure and dispersion of CdS QDs were successfully prepared through

an

one-step hydrothermal method using DMSO, ethylene glycol et al. as solvent [13, 2024]. However, using H2O as solvent in preparing graphene-CdS QDs is promising due

M

to its environmental friendly and low cost.

Glucose is an important analyte in clinical diagnostics and food analysis. Thus,

te

d

monitoring of glucose concentration by simple method is crucial to clinical medicine and environmental remedial remediation. Enzyme-based PEC biosensors have been

Ac ce p

widely used in glucose determination due to their high sensitivity, selectivity and minimal sample consumption. For example, using glucose oxidase (GOx) attached onto the surface of CdTe QDs photoanode, and the PEC sensor could detect glucose ranging from 0.1~11 mmol dm-3 with a detection limit of 0.04 mmol dm-3 [25].

Moreover, CdSe/ZnS QDs [26], ZnS/ITO thin-film [27] have also been used as enzymatic-based PEC biosensor for glucose detection. However, enzymatic-based PEC biosensor suffers from complicated procedures during enzyme immobilization and preservation, intrinsically insufficient stability of enzymes and easy inactivation by the external environment. Comparing with enzymatic-based PEC biosensor, non-

Page 3 of 30

enzymatic PEC detection method is a more promising method due to its higher stability and durability against external environmental [28-30]. Herein, GR-CdS QDs composites with different graphene dosages were prepared

QDs

based

photoelectrode

resulting

from

its

excellent

cr

graphene-CdS

ip t

through one-step hydrothermal method. A non-enzyme biosensor was fabricated using

us

photoelectrochemical activities. The biosensor showed good performance in the

2. Experimental

M

2.1 Synthesis of graphene-CdS quantum dots

an

monitoring of glucose with a sensitive, low detection limit and good selectivity.

All of the reagents were of analytical grade and were used without further

te

d

purification. Graphene oxide (GO) was prepared from natural graphite powder by using a modified Hummer’s method [31, 32]. And then, different amount of the as-

Ac ce p

prepared GO were dispersed into 70 mL water by ultrasonication to yield GO dispersions. The synthesis procedures of graphene-CdS QDs were based on a modified method as reported by Dong et al [9]. The samples were denoted as G0.1CdS, G0.5-CdS, G1.0-CdS and G2.0-CdS when the weight ratio of GO to Cd(CH3COO)2·2H2O was 0.1%, 0.5%, 1%, and 2%. As a control, pure CdS QDs were prepared via a similar procedure without GO dosage while keeping other experimental conditions unchanged. 2.2 Fabrication of graphene-CdS QDs modified ITO electrode Indium tin oxide (ITO) conductive glasses were treated by sonification

Page 4 of 30

respectively in absolute acetone, absolute ethanol and distilled water for several times. Then, 50 mg of graphene–CdS samples were dispersed in 5 mL of ethanol, and grounded in an agate mortar to form black viscous slurry. Finally, the slurry was

0.25 cm2, and then dried naturally.

us

2.3 Characterization and photoelectrochemical measurements

cr

ip t

dropped onto a piece of clean ITO glass by doctor blading method with a fixed size of

The phase structure of the products were characterized by X-ray diffraction

an

(XRD) using a Bruker advance-D8 with Cu Kα radiation. The TEM images were obtained on JEOL JSM-100, and the high-resolution transmission electron microscope

M

(HRTEM) images were observed on FEI Tecnai G220. The UV-Vis diffused reflectance spectra of the samples were obtained from a Perkin-Elmer Lambda 35

te

d

UV-Vis spectrometer. Moreover, Fourier transform infrared spectroscopy (FTIR, FTS40), and X-ray photoelectron spectroscopy (XPS) were also performed.

Ac ce p

The photoelectrochemical properties were obtained by computer-controlled

electrochemical workstation (CHI 660D, China) with a three-electrode configuration in 0.1 mol dm-3 NaOH with an irradiation of simulated AM 1.5 sunlight with an output power of 100 mW cm-2 produced by a solar simulator. Electrochemical impedance spectroscopy (EIS) was recorded in a 0.1 mol dm-3 KCl solution containing 5 mmol dm-3 K3Fe(CN)6/K4Fe(CN)6 (1:1) with a frequency range of 0.1~105 Hz at 0.2 V, the amplitude of the applied sine wave potential was 5 mV. 3. Results and discussion 3.1 Characterization of graphene-CdS photoelectrode

Page 5 of 30

X-ray diffraction (XRD) measurements were employed for the investigation of the phase and structure. As shown in Fig.1, the XRD pattern of the pristine GO (curve a) showed a sharp peak at 2θ=11.3◦, corresponding to the (001) reflection of graphite

ip t

oxide. The XRD pattern of CdS nanoparticles (curve b) indicated that all the

cr

diffraction peaks matched well with that of cubic CdS phase (JCPDS No. 42-1411).

us

XRD pattern of G0.5-CdS QDs (curve c) was in accordance to that of CdS nanoparticles (curve b), implying the cubic CdS phase. In addition, no diffraction

an

peak of graphene could be observed, suggesting the low amount and relatively low diffraction intensity of graphene.

M

Fig. 1

The morphology and size of G0.5-CdS were depicted by TEM images. A typical

te

d

TEM image of G0.5-CdS QDs was shown in Fig. 2a, and a highly dispersed of CdS QDs with average diameter of ~6 nm were attached onto graphene sheets and the

Ac ce p

particle size distribution was displayed in Fig. 2b. In the HRTEM image (Fig. 2c), the lattice fringes with interplanar distance of ~0.34 nm and ~0.21 nm could be assigned to the (111) and (220) plane of the cubic CdS. For comparison, pure CdS QDs prepared through the same method without GO dosage agglomerated and stacked randomly together (Fig. 2d). Therefore, it was supposed that the reduction of GO and the deposition of CdS QDs on graphene occurred simultaneously in the reaction. Accompanied with the reduction of GO, the graphene sheets played an important role as support material in assisting the growth and dispersion of the CdS QDs onto graphene surface. In the meantime, the CdS decoration, in turn, helped to prevent the

Page 6 of 30

aggregation of GR sheets. Fig. 2 Fig. 3 showed the FTIR of GO, PAA and G0.5-CdS QDs in the range of 4000-

ip t

500 cm-1. For GO, the strong band at ~3400 cm−1 and ~1407 cm−1 were assigned to

cr

the vibration of –OH groups. The band at ~1717 cm−1 was the C=O vibration of –

COOH located at the edge of GO sheets. The absorption band of –OH bending

us

vibration, epoxide groups and skeletal ring vibrations could be seen at ~1623 cm−1.

an

All of the peaks were characteristic vibration bands of GO, indicating the existence of hydroxyl, carboxyl, epoxide groups in GO. However, for G0.5-CdS QDs, the

M

representative adsorption bands of GO nearly disappeared, and other peaks of oxygencontaining functional groups (such as C=O) were reduced significantly, indicating the

d

reduction of GO. Simultaneously, the skeletal vibration absorption peak of graphene

te

was observed at ~1550 cm−1, confirming the recovery of the sp2 hybrid carbon

Ac ce p

skeleton [33, 34]. In addition, the characteristic absorption peaks of C=O stretching vibration (~1715 cm-1) and -CH2 deformation vibration (~1455 cm-1) indicated the residual of the bonded PAA in G0.5-CdS QDs. Fig. 3

X-ray photoelectron spectroscopy (XPS) is a surface analytical technique which

can provide useful information on the nature of functional groups and also on chemical composition of surfaces. Full XPS spectrum of GO and G0.5-CdS was shown in Fig. 4a, all binding energies were calibrated using the contaminant carbon (C 1s=284.6 eV) as reference. For GO, only peaks for C1s and O1s could be detected,

Page 7 of 30

while for G0.5-CdS QDs, the peaks for S 2s, S 2p, Cd 3p and Cd 3d were clearly observed except the peaks of C 1s and O 1s. In the high-resolution XPS of C 1s from GO (Fig. 4b), the four distinct peaks were ascribed to the following functional groups:

ip t

sp2 bonded carbon (C-C, 284.5 eV), epoxy/hydroxyls (C-OH, 285.9 eV), carbonyls

cr

(C-O, 286.6 eV) and carboxyl (O-C=O, 288.0 eV), indicating the high percentage of

us

oxygen-containing functional groups [35, 36]. In comparison, in the high-resolution XPS of C1s from G0.5-CdS QDs (Fig. 4c), the peak for C-O was almost disappeared,

an

and the intensities of the C-OH decreased dramatically, indicating the partial removal of the oxygen-containing functional groups. As for G0.5-CdS, the peak intensities of

M

O-C=O were increased due to the introduction of PAA. Fig. 4

te

d

The UV-Vis diffuse reflectance absorption spectra of GO, CdS and G0.5-CdS were shown in Fig. 5a. An enhanced absorption of G0.5-CdS QDs is observed, which

Ac ce p

is greater than that of CdS above 500 nm, indicating the combination of graphene with CdS QDs increased the visible light harvesting (Fig. 5a, curve a, b). It can be inferred that an enhanced photocurrent would be obtained for G0.5-CdS QDs than CdS nanoparticles. GO showed excellent light absorption in the range of 200~800 nm (Fig. 5a, curve a). Furthermore, the energy gap was estimated by a related curve of (αhv)1/2 versus photon energy (Fig. 5b). The bandgap energies of G0.5-CdS QDs and CdS were 2.05 eV and 2.22 eV respectively, indicating the introduction of graphene could narrow the energy gap due to the chemical bonding between semiconductor and graphene support [37]. Conclusively, the combination of graphene and CdS not only

Page 8 of 30

enhanced light absorption, but also expanded light absorbing range of the composite. As a result, more solar energy could be utilized in the G0.5-CdS QDs based

ip t

photoanode. Fig. 5

cr

3.2 Growth mechanism

us

The schematic of the synthesis of graphene-CdS hybrid materials was illustrated in Fig. 6. During the procedure, H2O, thiourea, and Cd(CH3COO)2·2H2O were used

an

as solvent, sulfur source and cadmium source respectively. It is well known that semiconductor QDs interact with GO through carboxylic acid functional groups,

M

while the carboxylic acid functional groups were mainly located at the edge of GO. So, it would be very difficult to obtain a homogeneous distribution of CdS QDs on

te

d

graphene sheets. Fortunately, PAA possessed abundance of carboxylic acid functional groups, the introduction of PAA could make CdS QDs distributing homogeneous on

Ac ce p

graphene sheets [13]. CdS QDs were linked onto graphene sheets through nonconvalent bonding, such as electrostatic interactions, hydrophobic interactions, which was confirmed by FTIR spectroscopy. In the meantime, the existence of ammonia could also reduce GO and stabilize the CdS QDs via attaching with the

negatively charged –COO- and OH- groups [38, 39]. Thus, the graphene sheets could be covered by CdS QDs with high coverage rate and homogenous distribution, which endowed G0.5-CdS with enhanced photoelectrochemical properties. Fig. 6

3.3 Optimization of experimental conditions

Page 9 of 30

To optimize the experimental conditions for glucose measurement, dosage of GO in graphene-CdS QDs, applied potential and film-thickness of graphene-CdS/ITO photoanode were investigated respectively. Fig. 7a showed the photocurrent of

ip t

graphene-CdS QDs with different dosage of GO. As the weight ratio of GO increased

cr

from 0 to 0.5%, the photocurrent increased from 32.6 μA cm-2 to 107.3 μA cm-2.

However, when the ratio of GO increased further to 2%, the photocurrent decreased to

us

45.8 μA cm-2. At a rather lower ratio of GO, photocurrent increased with the

an

increment of GO because the introduction of graphene facilitated the electron transport efficiently and suppressed the recombination of electron-holes pairs. As a

M

consequence, photocurrent increased with the increase of the dosage of GO at a rather lower ratio of GO. Moreover, graphene had strong light adsorption which can shield

te

d

active sites of CdS surface, and decreased the intensity of light through the depth of the reaction solution due to the “shielding effect” [40].

Ac ce p

To evaluate the interfacial charge transfer occurring on the surface of electrodes,

electrochemical

impedance

spectroscopy

(EIS)

of

graphene-CdS

hybrid

photoelectrode with different dosage of GO was carried out using K3Fe(CN)6

/K4Fe(CN)6 as a redox probe under simulated solar light. As shown in Fig. 7b, the incorporation of graphene could decrease the resistance of photoelectrode compared to the CdS/ITO electrode, which indicated that the interface resistance between the redox probe and electrode was decreased upon the incorporation of graphene. Moreover, the G0.5-CdS electrode showed the smallest electron-transfer resistance among all the electrodes.

Page 10 of 30

Applied potential was another important factor relevant to photocurrent response. Fig. 7c illustrated photocurrent intensity at different bias voltage. The photocurrent increased significantly when the potential increased from -0.2 V to 0 V (vs. SCE),

ip t

because the electron transferred from G0.5–CdS QDs to ITO would be prevented as a

cr

negative potential was used. On the contrary, when a positive bias voltage was used,

us

charge can be separated effectively and an oxidation reaction would take place on photoanode. Therefore, a higher photocurrent was obtained when a positive bias

an

potential was applied. As the potential increased from 0 V to 0.4 V, photocurrent changed slightly and the highest photocurrent was obtained when 0.2 V bias potential

M

was used. As shown in Fig. 7d, the photocurrent intensity increased as the thickness of photoanode increased from ~3 μm to ~10 μm. It was anticipated that photoanode with

te

d

higher film thickness contributed to higher light absorption. Afterward, photocurrent intensity decreased as the thickness of photoanode further increased from ~15 μm to

Ac ce p

~20 μm, indicating the excess photoanode thickness increased the recombination centers of charged carriers, which decrease the photocurrent. Conclusively, in this work, 0.5% dosage of GO (G0.5-CdS QDs), 0.2 V applied voltage and ~10 μm of film-thickness was chosen for further studies.

Fig. 7

3.4 The Mechanism of Photoelectrochemical detection of glucose Fig. 8

Page 11 of 30

The photocurrent of the photoanode was studied by employing the CdS and G0.5-CdS QDs modified ITO as photoanode. As shown in Fig. 8a, the CdS/ITO electrode showed photocurrent of 20 μA cm-2 under simulated solar illumination (Fig.

ip t

8a curve b). In addition, an obvious photocurrent spike in the curve at the initial time

cr

appeared, and then photocurrent decreased and reached a constant. In contrast, the

us

G0.5–CdS/ITO electrode showed a photocurrent of 82.4 μA cm-2 (Fig. 8a curve c), indicating the photocurrent was increased by the combination of graphene and CdS

an

QDs. Besides, the photocurrent spike almost disappeared, implying much higher light sensitivity as switching on and off the illumination for the G0.5-CdS/ITO electrode.

M

In this paper, glucose was used as model molecule, and the photocurrent of GR0.5-CdS/ITO electrode increased to 107.3 μA cm-2 and remained steady (Fig. 8a,

te

d

curve d). The photoelectrochemical process of the G0.5-CdS/ITO for glucose oxidation was proposed in Fig. 8b. Under illumination, CdS QDs were excited and

Ac ce p

underwent charge separation to yield electrons and holes (Eq. 1). Since the energy levels of conduction band (CB) of GR and ITO are lower than that of CdS, the electron transfer from the CB of CdS QDs to GR and then to ITO was energetically favorable process [41, 42]. Graphene, served as an excellent electron-transport matrix to capture and transport electrons from excited CdS to ITO rapidly, avoiding electronhole recombination and resulted in high light sensitivity. Moreover, photoexcited holes can be captured by OH- in strong alkaline electrolyte, in another word, OH- can

be oxidized by photoexcited holes to OH· (Eq. 2) [43]. Based on the two reasons mentioned above, glucose could be oxidized by OH· to gluconolactone, and

Page 12 of 30

photocurrent could be increased due to the separation of photoexcited electron-holes pairs. Moreover, the photocurrent response was not obviously decreased through all the repeating illumination−dark cycles. Therefore, it could be concluded that G0.5-

ip t

CdS/ITO can be applied to detect glucose with high sensitivity. Then, OH· served as

cr

strong oxidant to oxidize glucose, and H+ could be produced (Eq. 3). At last, H2 was

CdS+hν → CdS(h+ )+CdS(e_ ) _

OH +h+ → OH ⋅

us

produced in photocathode (Eq. 4). (1)

(2)

an

glucose+OH ⋅ → gluconolactone+H+ (3) 2H+ → H2

(4)

M

To further assess the photoelectrochemical behavior of G0.5-CdS QDs, the opencircuit (Voc) response to on-off cycle of solar irradiation was monitored. The photo-

te

d

voltage directly represented electron accumulation within the electrode system. The decay of the voltage upon removing the illumination represented the recombination

Ac ce p

process of the photogenerated electrons. Fig. 7c showed the Voc response of G0.5CdS/ITO electrode with and without glucose. The electron lifetime (τe) was

determined by fitting the Voc decay curves according to Eq.5 [44, 45]:

τe =

−1

K BT ⎛ dVOC ⎞ ⎜ ⎟         (5) e ⎝ dt ⎠

The dependence of electron lifetime (τe) of graphene-CdS photoelectrode on the VOC was shown in Fig. 8d. Obviously, with the existence of glucose, electron lifetime in the G-CdS QDs photoanode was prolonged compared to without glucose [46]. And thus, the recombination of photogenerated electron-holes pairs could be suppressed and photocurrent could be enhanced with existence of glucose.

Page 13 of 30

3.5 Photoelectrochemical detection of glucose

The photocurrent-time curve of G0.5-CdS/ITO electrode (Fig. 8) showed the response to glucose. In this paper, I0 and I represented the photocurrent of G0.5-

ip t

CdS/ITO electrode before and after addition of glucose. The photocurrent increased

cr

with the amount of glucose increased from 0.1 to 4.0 mmol dm-3 glucose. As shown in the

us

inset in Fig. 9, the (I-I0)/I0 gradually increased with the increment of the concentration of glucose. A good linear between (I-I0)/I0 and the concentration of glucose could be

an

obtained in the range of 0.1~4 mmol dm-3 with a detection limit of 7 μmol dm-3 at the signal-to-noise ratio (S/N) of 3. The linear regression equation was I((I-I0)/I0)

M

=0.081+0.222C glucose with a correlation coefficient of 0.9991. Hence, the proposed G0.5-CdS QDs based photoelectrochemical non-enzymatic biosensor showed

te

d

promising applications in glucose detection.

Fig. 9

Ac ce p

The interferences were investigated in the detection of glucose. With the addition

of 0.01 mmol dm-3 uric acid (UA), ascorbic acid (AA), NaCl, 4-acetamidophenol

(APAP), fructose, lactose, sucrose to the electrolyte aqueous solution with the existence of 0.5 mmol dm-3 glucose, only weaker current changes could be induced (Fig. 10). The results indicated that the effects of interferents were neglectable on the photoelectrochemical detection of glucose. In addition, the photocurrent of G0.5CdS/ITO electrode exhibited a little reduction after stored in air for two months. The results revealed that G0.5-CdS QDs sensing material also possessed high selectivity and durability in trace detection of glucose and could be potentially applied in clinical

Page 14 of 30

analysis of glucose.

Fig. 10 4. Conclusions

ip t

In summary, graphene-CdS QDs were successfully prepared via one-step

cr

hydrothermal method, wherein graphene served as supporting material as well as

us

electron collector and transporter. The G0.5-CdS/ITO electrode exhibited good photocurrent activities, and was used as a non-enzyme sensing platform to detection

an

glucose. The photoelectrochemical biosensor showed low applied potential of 0.2 V, wide linear range of 0.1~4 mmol dm-3 and low detection limit of 7 μmol dm-3 at the

M

signal-to-noise ratio (S/N) of 3. Furthermore, G0.5-CdS/ITO electrode also showed

te

Acknowledgments

d

excellent specificity for excluding the interference.

This work was supported by the Natural Science Foundation of China (Nos. 61176004,

Ac ce p

61204078), Program for Innovative Research Team (in Science and Technology) in University of Henan Province (No. 13IRTSTHN026), and the Key Project of Science and Technology of Henan Province (No. 122102210561, 13A150517 ).

References:

[1] Z. Yue, F. Lisdat, W.J. Parak, S.G. Hickey, L.P. Tu, N. Sabir, D. Dorfs, N.C. Bigall, Quantumdot-based photoelectrochemical sensors for chemical and biological detection, Acs Appl. Mater. Inter. 5 (2013) 2800. [2] W.W. Zhao, P.P. Yu, Y. Shan, J. Wang, J.J. Xu, H.Y. Chen, Exciton-plasmon interactions between CdS quantum dots and Ag nanoparticles in photoelectrochemical system and its

Page 15 of 30

biosensing application, Anal. Chem. 84 (2012) 5892. [3] F. Xu, Y.F. Yuan, H.J. Han, D.P. Wu, Z.Y. Gao, K. Jiang, Synthesis of ZnO/Ag/graphene

ip t

composite and its enhanced photocatalytic efficiency, CrystEngComm 14 (2012) 3615. [4] Y.Y. Bu, Z.Y. Chen, W.B. Li, J.Q. Yu, High-efficiency photoelectrochemical properties by a

cr

highly crystalline CdS-sensitized ZnO nanorod array, ACS Appl. Mater. Inter. 5 (2013) 5097.

us

[5] L.G. Bulusheva, A.V. Okotrub, Y.V. Fedoseeva, S.V. Larionov, A.A. Zarubanov, K.S. Zhurvlev, Electro- and photoluminescence of CdS nanoparticles deposited on carbon nanotubes, J.

an

Nanoelectron. Optoe. 8 (2013) 36.

[6] H. Choi, T. Duong, S. Yoon, Enhanced photoelectrochemical activity from visible light by

M

growing CdS/ITO nanocomposites onto single-walled carbon nanotubes, J. Electrochem. Soc. 160 (2013) H192.

te

d

[7] M. Zhong, D. Yang, J. Zhang, J.Y. Shi, X.L. Wang, C. Li, Improving the performance of CdS/P3HT hybrid inverted solar cells by interfacial modification, Sol. Energ. Mat. Sol. C 96

Ac ce p

(2013) 160.

[8] H. Li, Y. Tian, Z.F. Deng, Y. Liang, An in situ photoelectrochemical determination of hydrogen sulfide through generation of CdS nanoclusters onto TiO2 nanotubes, Analyst 137 (2012) 4605.

[9] P. Wang, X.Y. Ma, M.Q. Su, Q. Hao, J.P. Lei, H.X. Ju, Cathode photoelectrochemical sensing

of copper(II) based on analyte-induced formation of exciton trapping, Chem. Commun. 48 (2012) 10216. [10] C.H. Han, M.Y. Yan, L.Q. Mai, X.C. Tian, L. Xu, X. Xu, Q.Y. An, Y.L. Zhao, X.Y. Ma, J.L. Xie, V2O5 quantum dots/graphene hybrid nanocomposite with stable cyclability for advanced lithium batteries, Nano Energy 2 (2013) 916.

Page 16 of 30

[11] L.H. Yu, H. Ruan, Y. Zheng, D.Z. Li, A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity, Nanotechnology, 24 (2013)

ip t

375601. [12] Q.W. Huang, D.W. Zeng, H.Y. Li, C.S. Xie, Room temperature formaldehyde sensors with

cr

enhanced performances, fast response and recovery based on zinc oxide quantum dots/graphene

us

nanocomposites, nanoscale 4 (2012) 5651.

[13] P. Wang, T.F. Jiang, C.Z. Zhu, Y.M. Zhai, D.J. Wang, S.J. Dong, One-step, solvothermal

photovoltaic properties, Nano Res. 3 (2010) 794.

an

synthesis of graphene-CdS and graphene-ZnS quantum dot nanocomposites and their interesting

M

[14] P. Zeng, Q.G. Zhang, T.Y. Peng, X.H. Zhang, One-pot synthesis of reduced graphene oxide-

te

Phys. 13 (2011) 21496.

d

cadmium sulfide nanocomposite and its photocatalytic hydrogen production, Phys. Chem. Chem.

[15] S.G. Pan, X.H. Liu, CdS-Graphene nanocomposite : synthesis, adsorption kinetics and high

Ac ce p

photocatalytic performance under visible light irradiation, New J. Chem. 36 (2012) 1781. [16] J.P. Tian, H.M. Zhao, H.R. Zhao, X. Quan, Photoelectrochemical immunoassay for microcystin-LR based on a fluorine-doped tin oxide glass electrode modified with a CdS-graphene composite, Microchim. Acta 179 (2012) 163. [17] J.J. Yan, K. Wang, Q. Liu, J. Qian, X.Y. Dong, W. Liu, B.J. Qiu, One-pot synthesis of CdxZn1xS-reduced

graphene oxide nanocomposites with improved photoelectrochemical performance for

selective determination of Cu2+, RSC Adv. 3 (2013) 14451. [18] X.M. Zhao, S.W. Zhou, Q.M. Shen, L.P. Jiang, J.J. Zhu, Fabrication of glutathione photoelectrochemical biosensor using graphene-CdS nanocomposites, Analyst 137(2012)3697.

Page 17 of 30

[19] J.P. Tian, H.M. Zhao, H.R. Zhao, X. Quan, Photoelectrochemical immunoassay for microcystin-LR based on a fluorine-doped tin oxide glass electrode modified with a CdS-graphene

ip t

composite, Microchim. Acta 179 (2012) 163. [20] A. Cao, Z. Liu, S. Chu, M. Wu, Z. Ye, Z. Cai, Y. Chang, S. Wang, Q. Gong, Y. Liu, A Facile

cr

One-step method to produce graphene-CdS quantum dot nanocomposites as promising

us

optoelectronic materials, Adv. Mater. 22 (2010) 103.

[21] J. Chu, X. Li, J.Y. Qi, Hydrothermal synthesis of CdS microparticles-graphene hybrid and its

an

optical properties, CrystEngComm 14 (2012) 1881.

[22] N. Zhang, Y.H. Zhang, X.Y. Pan, X.Z. Fu, S.Q. Liu, Y.J. Xu, Assembly of CdS nanoparticles

M

on the two-dimensional graphene scaffold as visible-light-driben photocatalyst for selective organic transformation under ambient conditions, J. Phys.Chem. C 115 (2011) 23501.

Compd. 524 (2012) 5.

te

d

[23] X.W. Wang, H.W. Tian, Y. Yang, H. Wang, S.M. Wang, W.T. Zheng, Y.C. Liu, J. Alloy

Ac ce p

[24] S.G. Pan, X.H. Liu, CdS-graphene nanocomposite : synthesis, adsorption kinetics and high photocatalytic performance under visible light irradiation, New J. Chem. 36 (2012) 1781. [25] W.J. Wang, L. Bao, J.P. Lei, W.W. Tu, H.X. Ju, Visible light induced photoelectrochemical biosensing based on oxygen-sensitive quantum dots, Anal. Chim. Acta 744 (2012) 33.

[26] J. Tanne, D. Schaefer, W. Khalid, W.J. Parak, F. Lisdat, Light-Controlled Bioelectrochemical Sensor Based on CdSe/ZnS Quantum Dots, Anal. Chem. 83 (2011) 7778. [27] J. Du, X.P. Yu, Y. Wu, J.W. Di, ZnS nanoparticles electrodeposited onto ITO electrode as a platform for fabrication of enzyme-based biosensors of glucose, Mat. Sci. Eng. C 33 (2013) 2031. [28] Y. Wang, J. Chen, C.P. Zhou, L. Zhou, Y.Y. Kong, H.Y. Long, S. Zhong, A novel self-

Page 18 of 30

cleaning, non-enzymatic glucose sensor working under a very low applied potential based on a Pt nanoparticles-decorated TiO2 nanotube array electrode, Electrochim. Acta 115 (2014) 269.

ip t

[29] Y.J. Yang, J.F. Zi, W.K. Li, Enzyme-free sensing of hydrogen peroxide and glucose at a CuS nanoflowers modified glassy carbon electrode, Electrochim. Acta 115 (2014) 126.

cr

[30] X.M. Zhang, K.F. Huo, X. Peng, R.Z. Xu, P.H. Li, R.S. Chen, G. Zheng, Z.W. Wu, P.K. Chu,

us

WO3 nanoparticles decorated core-shell TiC-C nanofiber arrays for high sensitive and nonenzymatic photoelectrochemical biosensing, Chem. Comm. 49 (2013) 7091.

an

[31] W.S. Hummers, R.E. Offeman, Preparation of Graphitic Oxide, J. Am. Chem. Soc. 80 (1958) 1339.

M

[32] C. Nethravathi, M. Rajamathi, Chemically modified graphene sheets produced by the solvothermal reduction of colloidal dispersions of graphite oxide, Carbon 46 (2008) 1994.

te

d

[33] C. Nethravathi, T. Nisha, N. Ravishankar, C. Shivakumara, M. Rajamathi, Graphenenanocrystalline metal sulphide composites produced by a one-pot reaction starting from graphite

Ac ce p

oxide, Carbon 47(2009)2054.

[34] H.K. Jeong, Y.P. Lee, R.J. Lahaye, M.H. Park, K.H. An, I.J. Kim, C.W. Yang, C.Y. Park, R.S. Ruoff, Y.H. Lee, Evidence of graphitic AB stacking order of graphite oxides, J. Am. Chem. Soc. 130 (2008) 1362.

[35] S. Stankovich, R.D. Piner, X.Q. Chen, N.Q. Wu, S.T. Nguyen, R.S. Ruoff, Stable aqueous dispersions of graphitic nanoplatelets via the reduction of exfoliated graphite oxide in the presence of poly(sodium 4-styrenesulfonate), J. Mater. Chem. 16 (2006) 155. [36] S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y.Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Synthesis of graphene-based nanosheets via chemical reduction of exfoliated

Page 19 of 30

graphite oxide, Carbon 45 (2007) 1558. [37] Y.P. Zhang, C.X. Pan, TiO2/graphene composite from thermal reaction of graphene oxide and

ip t

its photocatalytic activity in visible light, J. Mater. Sci. 46 (2011) 2622. [38] K. Jasuja, V. Berry, Implantation and growth of dendritic gold nanostructures on graphene

cr

derivatives: Electrical property tailoring and raman enhancement, ACS Nano 3 (2009) 2358.

us

[39] X.J. Zhou, J.L. Zhang, H.X. Wu, H.J. Yang, J.Y. Zhang, S.W. Guo, Reducing graphene oxide via hydroxylamine: A Simple and Efficient Route to Graphene, J. Phys. Chem. C 115 (2011)

an

11957.

[40] Q. Li, B.D. Guo, J.G. Yu, J.R. Ran, B.H. Zhang, H.J. Yan, J.R. Gong, Highly efficient visible-

J. Am. Chem. Soc. 133 (2011) 10878.

M

Light-Driven photocatalytic hydrogen production of CdS-cluster-decorated graphene nanosheets,

te

d

[41] W. Zhang, Y.R. Shi, L.B. Gan, C.H. Huang, H.X. Luo, D.G. Wu, N.Q. Li, PH-dependent photoinduced electron transfer at C60-EDTA Langmuir−Blodgett film modified ITO electrode, J.

Ac ce p

Phys. Chem. B 103 (1999) 675.

[42] R. Gill, F. Patolsky, E. Katz, I. Willner, Electrochemical control of the photocurrent direction in intercalated DNA/CdS nanoparticle systems, Angew. Chem. Int. Ed. 44 (2005) 4554. [43] X.M. Zhao, S.W. Zhou, L.P. Jiang, W.H. Hou, Q.M. Shen, J.J. Zhu, Graphene-CdS nanocomposites: Facile Oone-Step synthesis and enhanced photoelectrochemical cytosensing, Chem.–Eur. J. 18 (2012) 4974. [44] A. Zaban, M. Greenshtein, J. Bisquert, Determination of the electron lifetime in

nanocrystalline dye solar cells by open-circuit voltage decay measurements, ChemPhysChem 4 (2003) 859.

Page 20 of 30

[45] J. Bisquert, A. Zaban, M. Greenshtein and I. Mora-Sero, Determination of rate constants for charge transfer and the distribution of semiconductor and electrolyte electronic energy levels in

ip t

dye-sensitized solar cells by open-circuit photovoltage decay method, J.Am. Chem. Soc. 126 (2004) 13550.

cr

[46] D.R. Baker, P.V. Kamat, Disassembly, reassembly, and photoelectrochemistry of etched TiO2

Ac ce p

te

d

M

an

us

nanotubes, J. Phys. Chem. C 113 (2009) 17967.

Page 21 of 30

Figure captions

ip t

Fig. 1 XRD patterns of (a) GO, (b) CdS, (c) G0.5-CdS. Fig. 2 (a) Typical TEM image of G0.5-CdS; (b) The particle size distribution obtained from TEM

cr

statistics; (c) HRTEM image of G0.5-CdS; (d) Typical TEM image of CdS.

Fig. 3 Fourier transformation infrared (FTIR) spectra of (a) GO, (b) PAA and (c) G0.5-CdS in the

us

range of 4000–500 cm-1.

spectra of C 1s from GO and (c) G0.5-CdS.

an

Fig. 4 (a) Representative XPS survey spectrum of GO and G0.5-CdS; (b) High-resolution XPS

energy gap of CdS and G0.5-CdS QDs.

M

Fig. 5 (a) UV-Vis diffuse reflectance absorption spectra of GO CdS and G0.5-CdS; (b) Calculated

hydrothermal process.

te

d

Fig. 6 Schematic illustration of the synthesis process of graphene-CdS QDs via one-step

Ac ce p

Fig. 7 Effects of (a) mass ratio of GO, (b) Nyquist plots of different electrodes, (c) applied potential (vs. SCE) and (d) film-thickness of electrode on photocurrent response of graphene-

CdS/ITO electrode in 0.1 M NaOH containing 1 mmol dm-3 glucose. Fig. 8 (a) Photocurrent response of ITO, CdS/ITO and G0.5-CdS/ITO with and without glucose; (b) Schematic illustration of photoelectrochemical process for oxidation of glucose at G0.5CdS/ITO electrode; (c) Open-circuit voltage response of G0.5-CdS/ITO electrode to illumination on and off. (d) Electron recombination lifetime versus open-circuit potential for G0.5-CdS/ITO with absence and existence of 1 mmol dm-3 glucose. Fig. 9 Photocurrent response of G0.5-CdS/ITO electrode in 0.1 mol dm-3 NaOH in the presence of

Page 22 of 30

0, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4.0 mmol dm-3 glucose (from bottom to top) at 0.2 V under the irradiation of simulated solar energy. Inset: linear calibration curve. Fig. 10 Photocurrent ratio I/I0 of G0.5-CdS/ITO electrode in 0.1 M NaOH containing 0.5 mmol

ip t

dm-3 glucose in the presence of various interferent species at 0.2 V to visible-light irradiation (I0

cr

and I are the photocurrents of the G0.5-CdS/ITO electrode before and after addition of

Ac ce p

te

d

M

an

us

interferents).

Page 23 of 30

Figures

an

us

cr

ip t

Fig. 1

M

251658240

Ac ce p

te

d

Fig. 2

251658240

Page 24 of 30

an

us

cr

ip t

Fig. 3

251658240

Ac ce p

te

d

M

Fig. 4

251658240

Page 25 of 30

us

cr

ip t

Fig. 5

Ac ce p

te

d

M

an

Fig. 6

Page 26 of 30

an

us

cr

ip t

Fig.7

M

251658240

Ac ce p

te

d

Fig. 8

251658240

Page 27 of 30

us

cr

ip t

Fig. 9

an

251658240

Ac ce p

te

d

M

Fig. 10

251658240

Page 28 of 30

Highlights: (1) GR-CdS hybrid materials were prepared via one-step hydrothermal method. (2) GR-CdS was used as non-enzymatic photoelectrochemical sensor to detect

ip t

glucose.

Ac ce p

te

d

M

an

us

cr

(3) Glucose in real sample was detected and showed good specificity and sensitivity.

Page 29 of 30

Ac

ce

pt

ed

M

an

us

cr

i

Graphical Abstract (for review)

Page 30 of 30