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Sensors and Actuators B 194 (2014) 303– 310

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l h om epage: www.elsev ier .com/ locat e/snb

ovel electrochemical sensing platform based on molybdenumisulfide nanosheets-polyaniline composites and Au nanoparticles

e-Jing Huang ∗, Ji-Zong Zhang, Yu-Jie Liu, Ling-Ling Wangollege of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, China

r t i c l e i n f o

rticle history:eceived 7 November 2013eceived in revised form6 December 2013ccepted 26 December 2013vailable online 4 January 2014

eywords:raphene-like molybdenum

a b s t r a c t

Two-dimensional (2D) transition metal dichalcogenide nanosheets offer unique electronic properties andattract increasing attention in electrochemical sensing. In this paper, graphene-like MoS2–polyaniline(PANI) composites were synthesized by a facile hydrothermal method and a simple in situ polymeriza-tion procedure. MoS2 served as a 2D conductive skeleton that supported a highly electrolytic accessiblesurface area of redox-active PANI and provided a direct path for electrons. A novel electrochemicalsensor was subsequently developed for the determination of dopamine based on MoS2-PANI compos-ites and gold nanoparticles (AuNPs) modified glassy carbon electrode (AuNPs/MoS2–PANI/GCE). TheAuNPs/MoS2–PANI/GCE showed an enhanced electrocatalytic activity toward the oxidation of dopamine

isulfide-polyaniline compositesu nanoparticleslectrochemical sensoropamine

when compared with bare electrode and other modified electrode. It exhibited a good electrocatalyticoxidation toward dopamine in the linear response range from 1 to 500 �M with the detection limit of0.1 �M (S/N = 3). The developed electrochemical sensor was successfully applied to the dopamine detec-tion in human urine sample, which proved that it was a versatile sensing tool for the detection of DA inreal samples. This work indicated that MoS2–PANI composites were promising in electrochemical sensing

.

and catalytic applications

. Introduction

With a single- or few-layer-structured graphite, graphene hasttracted wide attention due to its high specific surface area, excel-ent electrical conductivity, good chemical stability and strong

echanical strength. These properties make it an attractive can-idate for fabricating various functional devices, such as sensors,hotovoltaics and photodetectors [1–3]. The successful fabrica-ion of graphene based devices has stimulated new interests inraphene-like two-dimensional (2D) materials of elements otherhan carbon to expect to obtain some unusual properties. Indeed,D layer-structured materials such as MoS2, VS2, SnS2 and WS2ave been widely used as lubricants, catalysts, electrode materials

or capacitors, sensor, and lithium-ion batteries [4–7]. Their uniqueroperties are associated with exotic electronic properties and highpecific surface areas that are crucially important for energy stor-ge, catalysis, sensing, and field-emitting applications.

From the structural point of view, MoS2 is a typical familyember of transition-metal dichalcogenides. It is composed of Mo

etal layers sandwiched between two sulfur layers and stacked

ogether by weak Van der Waals interactions [8,9]. The layer-tructure MoS2 is expected to act as an excellent functional material

∗ Corresponding author. Tel.: +86 376 6390611.E-mail address: kejinghuang@163.com (K.-J. Huang).

925-4005/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2013.12.106

© 2014 Elsevier B.V. All rights reserved.

because the 2-dimensional electron–electron correlations amongMo atoms would aid in enhancing planar electric transporta-tion properties. Indeed, MoS2 has attracted considerable attentiondue to its extensive applications as catalysts, lubricants, lithiumbattery, supercapacitor, and so on [10–13]. However, few atten-tions have been put into its application as an electrode materialfor electrochemical sensor because the electronic conductivity ofMoS2 is still lower compared to carbon nanotube/graphene [14].Furthermore, like graphene, MoS2 nanosheets tend to form agglom-erates through the Van der Waals interactions, which greatlyrestricts its further application in electrochemical sensing. There-fore, the functionalization of MoS2 nanosheets to prevent thehappening of aggregation is very important for enlarging its appli-cation in electrochemical sensor. The surface functionalizationwith conductive polymer can be a good way because the sol-ubility and dispersibility of MoS2 nanosheets would be greatlyimproved by this protocol, meanwhile the unique properties ofMoS2 nanosheets are remained. For example, Ma et al. has syn-thesized polypyrrole/MoS2 composites and used as an advancedelectrode material for high-performance supercapacitors applica-tions [13].

Polyaniline (PANI) is one of the most promising conducting

polymers primarily due to its low cost, easy preparation, uniqueproperties which are easily controlled by oxidation and pro-tonation, excellent environmental stability, and high chemicaldurability [15]. These special features have made PANI widely used

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shape of the prepared MoS2. The inset of Fig. 1A exhibits the struc-ture of few-layer sheets of the obtained MoS2 and its thickness

04 K.-J. Huang et al. / Sensors an

n various kinds of electrochemical applications such as enzymeased biosensor for detection of water pollution, gas sensor foretermination of NO2 and voltammetric sensor for detection ofpinephrine and uric acid [16–18].

Dopamine (DA) is an important catecholamine neurotransmit-er and mainly exists in the brain and central nervous system of

ammals [19]. It plays a very important role in the functioningf central nervous, hormonal, renal and cardiovascular systems.bnormal level of DA is believed to be associated with certain neu-ological disorders known as schizophrenia, Parkinson and drugddiction [20]. The rapid and accurate detection and quantificationf DA is important in disease diagnosis. Au nanoparticles (AuNPs)re mostly recommended owing to the fact that they can greatlyncrease the current response of the modified sensor with a goodonductive ability [21].

In this work, 2D flower-like MoS2 were prepared by a sim-le hydrothermal method, and then MoS2–PANI composites wereynthesized via in situ polymerization of aniline monomer in theresence of MoS2 nanosheets suspension. A novel electrochemi-al sensing platform for sensitive detection of DA was constructedy assembling MoS2–PANI composites and AuNPs on glassy carbonlectrode (GCE). Taking advantages of MoS2–PANI composites anduNPs signaling amplification, this electrochemical sensor showed

low detection limit and wide linear range, and it had been appliedor assay of DA in human urine samples with satisfactory results.

. Experimental

.1. Apparatus

Electrochemical measurements were performed on a CHI 660Dlectrochemical Workstation (Shanghai, CH Instruments, China)ith a conventional three-electrode system composed of a plat-

num wire as an auxiliary electrode, a saturated calomel electrodeSCE) as a reference electrode and a 3-mm diameter GCE as aorking electrode. The morphologies of the nanocomposite were

ecorded on a JEM 2100 transmission electron microscope (TEM)nd a Hitachi S-4800 scanning electron microscope (SEM). Fourierransform infrared spectroscopy (FT-IR) was measured on a Bruker-ensor 27 IR spectrophotometer. Thermogravimetric analysis (TGA,DTQ600) was performed under a nitrogen atmosphere at a heatingate of 10 ◦C min−1.

.2. Reagents

Na2MoO4·2H2O, l-cysteine, (NH4)2S2O8 and aniline were pur-hased from Shanghai Chemical Reagent Corporation (Shanghai,hina). Chloroauric acid (HAuCl4·4H2O), DA, uric acid andrisodium citrate were purchased from Sigma-Aldrich (St. Louis,

O). Phosphate buffer solutions (PBS, 0.1 M) with various pH valuesere prepared with Na2HPO4 and NaH2PO4 and adjusted by 0.1 M3PO4 or 0.1 M NaOH solutions. All reagents were of analyticalrade or better. Aqueous solutions were prepared from deionizedater.

.3. Preparation of Au nanoparticles

The AuNPs with about 13-nm diameter were synthesizedccording to the previous protocol [22]. In short, 100 mL HAuCl4olution (0.01%) was boiled with vigorous stirring, and then 2.5 mLrisodium citrate solution (1%) was quickly added. The solutionurned to deep red, indicating the formation of AuNPs. Upon con-

inued stirring and cooling own, the AuNPs solution was obtainednd stored in brown glass bottles at 4 ◦C before use.

ators B 194 (2014) 303– 310

2.4. Synthesis of MoS2 and MoS2–PANI composites

The MoS2 and MoS2–PANI composites were synthesized accord-ing our previous work [23]. Briefly, 0.30 g Na2MoO4·2H2O wasfirstly dissolved in 40 mL deionized water under stirring. Afteradjusting the pH value to 6.5 with HCl, 0.80 g l-cysteine was addedand the mixture was then diluted to 80 mL with water. After vio-lently stirring for about 1 h, the mixture was transferred into a100 mL Teflon-lined stainless steel autoclave and heated at 180 ◦Cfor 48 h. After cooling, the MoS2 nanosheets were collected by filtra-tion, washed with distilled water and absolute ethanol for severaltimes, and then dried in vacuum at 60 ◦C for 24 h.

The MoS2–PANI composites were synthesized by in situ chem-ical oxidative polymerization directed by molybdenum disulfidenanosheets. Firstly, 0.02 g the as-prepared MoS2 nanosheets wereultrasonically dispersed in 30 mL HCl solution (1 M). Then, themixture was transferred into ice bath, cooled to below 5 ◦C. Sub-sequently, 0.92 mL aniline, 20 mL HCl solution (1 M) and 10 mLethanol were dispersed in 50 mL deionized water under stirringin an ice-bath. After 10 min, 20 mL (NH4)2S2O8 solution (1 M) wasadded drop by drop within 1 h. The reaction was performed understirring for 12 h in an ice-bath. Finally, the suspension was fil-tered and rinsed several times with deionized water and ethanolto remove retained aniline monomer and oxidant. The MoS2–PANIcomposites were obtained after dried in vacuum at 60 ◦C for 24 h.

2.5. Preparation of modified electrodes

Prior to use, the GCE was first polished with alumina slurry(0.5 �m followed by 0.05 �m) and ultrasonically cleaned withwater and ethanol, respectively. A stock solution of 1 mg mL−1

MoS2–PANI was prepared by dispersing 1 mg MoS2–PANI compos-ites in 1 mL DMF. Then 10 �L as-prepared suspension was appliedon the pretreated GCE with a microsyringe and dried under aninfrared lamp to obtain the modified electrode MoS2–PANI/GCE.After that, the MoS2–PANI/GCE was incubated in AuNPs solu-tion (3 mL, 2.5 nM) for 8 h at room temperature to prepareAuNPs/MoS2–PANI/GCE.

The procedure for the electrochemical sensor fabrication is illus-trated in Scheme 1.

2.6. Electrochemical measurements

Cyclic voltammetry (CV) method was performed in the potentialrange from −0.2 to 0.8 V at a scan rate of 100 mV s−1. Differen-tial pulse voltammetry (DPV) measurement was performed in thescan range from −0.2 to 0.6 V, with the pulse amplitude of 50 mV,pulse width of 50 ms and pulse period of 0.2 s. Electrochemicalimpedance spectroscopy (EIS) experiment was carried out in a10.0 mL aqueous solution containing 5 mmol L−1 of [Fe(CN)6]3−/4−

and 0.1 mol L−1 of KCl at a potential of 0.2 V over the frequencyrange from 0.1 Hz to 100 kHz, using an amplitude of 5 mV.

3. Results and discussion

3.1. Characterization of MoS2–PANI composites

The MoS2–PANI composites were prepared by a facilehydrothermal method and a simple in situ polymerization proce-dure. Fig. 1A and B display the SEM images of the as-prepared MoS2nanosheets and MoS2–PANI composites. Fig. 1A reveals few-layerflexible wrinkled sheets of the MoS2, illustrating the flower-like

is about 3–5 monolayers judged from the inset of Fig. 1A. Theresults indicated that the MoS2 nanosheets have large specific

K.-J. Huang et al. / Sensors and Actuators B 194 (2014) 303– 310 305

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spcwwttfsnelfwc

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Scheme 1. Schematic diagr

urface areas, combining with its specific electronic and opticalroperties [24], and could be a good candidate for electrochemi-al sensor construction. The SEM image of MoS2–PANI compositesere shown in Fig. 1B. Many random nanosheets agglomerateere observed. The nanosheets showed more thick and bigger

han pure MoS2 nanosheets. In order to reveal the fine microstruc-ure, the as-synthesized MoS2 and MoS2–PANI composites wereurther characterized by TEM. The single MoS2 sheet with theize about 200 nm was shown in Fig. 1C. From Fig. 1D, the MoS2anosheets were embedded in PANI, with some possessing foldeddges corresponding to the different layers of MoS2 sheets. Theayer agglomerates of PANIs anchored onto MoS2 sheets was help-ul to improve the solubility and dispersibility of MoS2, whichould have positive effects on the improvement in the electro-

hemical performances of MoS2–PANI composites.The TGA measurement was carried out to study the ther-

al stability of MoS2 and MoS2–PANI composites (Fig. 1E). Theoth materials had an initial mass loss around 100 ◦C, which wasttributed to the evaporation of surface absorbed water molecules.or the MoS2 nanosheet, it was observed that it lost 27% of its weightrom 100 ◦C to 395 ◦C, which was associated with the dopant HClnd water in the MoS2 nanosheets. The initial decomposition tem-erature of the MoS2–PANI composites was about at 295 ◦C, whichas attributed to the loss of co-intercalated water molecules and

he liberation of co-intercalated HCl. An obviously weight loss ofhe MoS2–PANI composites at the range of 295–457 ◦C was mainlyelated to the degradation and decomposition of PANI.

FT-IR spectra of MoS2 nanosheets and MoS2–PANI compositesere compared between 4000 and 500 cm−1 (Fig. 1F). In the

urve of MoS2–PANI composites, the peak observed at 1580nd 1550 cm−1 were C=C stretching deformation of quinoid andenzene rings, respectively [25], and the peaks at 1310, 1250nd 1120 cm−1 were attributed to C–N stretching of secondary

the electrochemical sensor.

aromatic amine and the aromatic C–H in-plane bending. The bandsat 790 cm−1 was assigned to the out-of-plane deformation of C–H inthe 1,4-disubstituted benzene ring [26]. In the spectra of MoS2 andMoS2–PANI composites, the bands at about 590 cm−1 was assignedto Mo–S vibration [27]. The difference on the intensity of the OHvibration at 3420 cm−1 indicated that the free hydroxy groupsdecreased after PANI coating at MoS2. These results indicated theMoS2–PANI composites have been successfully prepared.

3.2. Electrochemical behavior of DA on AuNPs/MoS2–PANI/GCE

CVS of DA were investigated with different electrodes.The voltammetric responses toward 0.2 mM DA were mea-sured for three electrodes: GCE, MoS2–PANI/GCE, andAuNPs/MoS2–PANI/GCE. The results were shown in Fig. 2A.On the bare GCE (curve a), an anodic peak of DA with peak current(Ipa) about 1.5 �A appeared at 0.1 V, and a cathodic peak withpeak current (Ipc) about 3.2 �A appeared at 0.18 V. By contrast,the MoS2–PANI/GCE (curve b) gave a relatively big anodic peak at0.04 V with Ipa of about 2.3 �A and cathodic peak at 0.17 V with Ipc

of about 5.1 �A, that was approximately two times than the bareGCE, suggesting MoS2–PANI film acted as a accelerator for electrontransfer of DA. At AuNPs/MoS2–PANI/GCE (curve c), a pair of well-defined redox peaks were observed at Epa = 0.1 V and Epc = 0.17 V.70 mV of peak potential difference (�Ep) between anodic andcathodic peak demonstrated that the AuNPs/MoS2-PANI compos-ites facilitated the electron transfer of DA. Compared with the bareGCE and MoS2–PANI/GCE, the AuNPs/MoS2–PANI/GCE presenteda more negative potential for oxidation of DA, indicating a distinct

electrocatalytic activity toward DA. Obviously, Ipa and Ipc peakcurrents further increased at AuNPs/MoS2–PANI/GCE comparedwith Gr/GCE and MoS2–PANI/GCE, which indicated this well-defined AuNPs/MoS2–PANI film possessed the requisite surface

306 K.-J. Huang et al. / Sensors and Actuators B 194 (2014) 303– 310

Fig. 1. SEM images of MoS nanosheets (A) and MoS –PANI composites (B); TEM images of MoS nanosheets (C) and MoS –PANI composites (D); TGA plots of the MoS andM T-IR s

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oS2–PANI composites at a heating rate of 10 ◦C min−1 under N2 atmosphere (E); F

tructure and electronic properties to support rapid electron trans-er for this redox system. The nanocomposite could offer effectiveensing platform for the sensitive electrochemical determinationf DA. DPV was also applied to investigate the electrochemicalehavior of DA at the bare GCE (a), MoS2–PANI/GCE (b), anduNPs/MoS2–PANI/GCE (c), and the similar results were obtained

Fig. 2B).EIS was used to characterize different electrodes. In EIS,

Fe(CN)6]3−/4− was utilized as the redox probe and the diameterf a semicircle in a Nyquist plot (e.g., see Fig. 2C) correspondedo an electron transfer resistance, Rct. In 0.1 M KCl containing

2 2 2

pectra of MoS2 nanosheets and MoS2–PANI composites (F).

5.0 mM [Fe(CN)6]3−/4−, GCE displayed a small semicircle at highfrequencies and a linear Nyquist plot at low frequencies (curvea), suggesting very low Ret (400 �) to redox probe [Fe(CN)6]3−/4−.When MoS2–PANI composites were immobilized on the bareelectrode, Ret decreased to about 250 � (curve b), indicatingthe good electron conductivity of MoS2–PANI composites. Forthe AuNPs/MoS2–PANI/GCE, the Ret further decreased (curvec) (Ret = 100 �), which showed that the AuNPs facilitated the

[Fe(CN)6]3−/4− ions transfer due to its good conductivity. Bothresults of EIS and CV proved AuNPs/MoS2–PANI composites filmhad the good electrochemical performance.

K.-J. Huang et al. / Sensors and Actuators B 194 (2014) 303– 310 307

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ig. 2. CVs (A) and DPVs (B) of different electrodes in 0.1 M PBS (pH 7.0) containingith the frequency sweep from 104 to 0.1 Hz. (a) bare GCE, (b) MoS2–PANI/GCE, (c)

.3. Effect of pH and scan rate

The effect of pH on the peak current and the peak potentialf DA at the AuNPs/MoS2–PANI composites were investigated inH range from 3.0 to 8.0. Fig. 3A shows CVs of DA obtained atuNPs/MoS2–PANI/GCE in various pH solutions containing 0.2 mMA. The CVs were performed in the potential range from −0.2 to0.8 V at the scan rate of 100 mV s−1. The oxidation peak currentf DA increased with lower to higher pH and reached its maximumxidation peak current at pH 7.0. Therefore, pH 7.0 was taken ashe optimum solution pH for the electrochemical oxidation of DA.

Furthermore, we investigated the peak potential of DA withespect to the different pH solutions (pH 3.0–8.0). The oxida-ion peak potential had a linear relationship with pH valueFig. 3B), clearly indicating that the electrocatalysis of the DA athe AuNPs/MoS2–PANI/GCE was a pH dependent reaction. The lin-ar regression equation was: Epa (mV) = 498.4–49.6 pH (R = 0.9971).his slope value was a close relation to the theoretical valueor an equal number of proton and electron transport process−59 mV pH−1 at 25 ◦C) [28], indicating protons were directlynvolved in the overall oxidation reactions, i.e., the oxidation reac-ions occurred via electrontransfer step followed by protonationrocess.

The effect of scan rate on the electrochemical responses ofA at the AuNPs/MoS2–PANI/GCE was studied (Fig. 3C) at differ-nt scan rates (100–700 mV s−1). Upon increasing the scan rates,

he anodic and cathodic peak current increased linearly. Mean-hile, the anodic and cathodic peak potentials were shifted slightly.oreover, both anodic and cathodic peak currents increased lin-

arly when the scan rates increased from 100 to 700 mV s−1.

M DA; (C) EIS of different electrodes in 5.0 mM [Fe(CN)6]3−/4− containing 0.1 M KCls/MoS2-PANI/GCE.

The peak potentials shifted slightly toward the positive and thenegative direction at higher scan rates, suggesting that DA oxida-tion processes at the composite electrode were surface-confinedelectrochemical process not diffusion controlled electrochemicalprocess.

3.4. Analytical performance of designed electrochemical sensor

DPV was used for the determination of DA atAuNPs/MoS2–PANI/GCE in the potential range of −0.2 to 0.6 V atthe scan rate of 100 mV s−1. Fig. 4A shows the DPVs obtained atAuNPs/MoS2–PANI/GCE for different DA concentrations in pH 7.0.The anodic peak current of DA increased linearly with increasingthe concentrations of DA over the range of 1.0–500 �M (Fig. 4B). Thecorresponding regression equation was ip (�A) = −0.591–0.0274C(�M) with a correlation coefficient of 0.9933. The limit of detection(LOD) was estimated to be 0.1 �M (S/N = 3). The analytical perfor-mance of this fabricated electrode was compared with previouslyreported different modified electrodes for the determination of DA[29–34]. The results were presented in Table 1. It could be seen thatthe developed sensor was more comparable and even exhibitedbetter analytical performance toward DA than previously reportedother DA sensors.

The potential application of AuNPs/MoS2–PANI/GCE for otheranalytes was also investigated. As shown in Fig. 4C, two ana-

lytes including DA and uric acid displayed well-defined DPVpeaks with good separations from each other, indicating theAuNPs/MoS2–PANI composites had potential for other electro-chemical sensor design.

308 K.-J. Huang et al. / Sensors and Actuators B 194 (2014) 303– 310

F ses (Ai ons.

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ig. 3. The effect of pH value of the substrate solution on the amperometric responn the figures is the average of four experiments carried out under the same conditi

.5. Repeatability, stability and interference

To evaluate the repeatability of the AuNPs/MoS2–PANI/GCE,he peak currents of 10 successive measurements by DPV in

10 �M DA solution was determined. The relative standardeviation (R.S.D.) of 1.8% was obtained, indicating that theuNPs/MoS2–PANI/GCE was not subject to surface fouling by thexidation products. Six parallel-made AuNPs/MoS2–PANI modifiedlectrodes were used to detect 10 �M DA, respectively. The R.S.D.f the sensor was 4.5%, indicating a satisfactory reproducibilityould be obtained by this novel electrochemical sensing plat-orm.

The stability of the developed sensor was investigated. After0 cyclic runs, the voltammetric response to 10 �M DA almost

emained 95% of the initial response. The storage stability of theroposed sensor was also evaluated. When not in use, the elec-rode was suspended above PBS at 4 ◦C in a refrigerator. After 5nd 10 days, the sensor retained 94% and 91% of its initial response

able 1omparison between the proposed sensor and other reported sensor for DA detection.

Electrode materials Analytical tech

Pyrogallol red DPV

Multi-walled carbon nanotubes DPV

Poly(phenosafranine) DPV

AuNPs/overoxidized polypyrrole DPV

5-Hydroxytryptophan DPV

Acetylcholine DPV

Graphene-AuNPs-chitosan/silica sol–gel hybrid membranes DPV

AuNPs/MoS2-PANI composites DPV

) and Epa (B); (C) the plot of the peak current vs scan rates. Each experimental point

current of 10 �M DA, respectively, indicating a long lifetime of theAuNPs/MoS2–PANI film.

Possible interference for the detection of DA atAuNPs/MoS2–PANI/GCE was investigated by addition of vari-ous compounds to 0.1 M PBS in the presence of 10 �M DA. Theoxidation peak current of DA was individually measured in thepresence of different concentrations of interferents and then thechange of peak current was checked. It was found that 200-foldconcentrations of glucose, glycine, l-cysteine, glutathione, vitaminC, citric acid, and tartaric acid, 2-fold concentrations of ascorbicacid and uric acid almost had no influence on the detection of DA(the peak current change was below 5%), revealing that this newsensing platform had good selectivity to DA.

3.6. Detection of urine samples

In order to verify the reliability of the method for analysis ofDA, the human urine sample was diluted 500 times with 0.1 M

nique Linear range (�M) LOD (�M) References

2.5–10 0.08 [29]0.5–10 0.1 [30]50–500 20 [31]0.75–20 0.15 [32]0.5–30 0.31 [33]0.7–5 0.3 [34]1–200 0.3 [35]1–500 0.1 This work

K.-J. Huang et al. / Sensors and Actuators B 194 (2014) 303– 310 309

Fig. 4. (A) DPV profiles at AuNPs/MoS2-PANI/GCE in PBS (pH 7.0) different concentrationoxidation peak current as a function of DA concentrations; (C) DPVs of different concentto h: 240, 280, 300, 350, 370, 420, 470, 500 �M for DA and 360, 400, 440, 480, 500, 550, 5

Table 2Determination of DA in human urine sample with developed method.

Sample no. Added (�M) Found (�M) RSD (%) Recovery (%)

1 0 –5 4.7 3.8 93.0

30 31.3 2.7 104.3100 96.2 4.2 96.2

2 0 –5 4.6 3.6 92.0

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4

cuAft

30 29.1 3.2 97.0100 103.4 2.8 103.4

BS (pH = 7.0) to be the real samples with DPV. No other pre-reatment process was performed. To ascertain the correctnessf the results, the diluted sample mentioned above was spikedith certain amounts of DA and then was detected. The analytical

esults were summarized in Table 2. The recovery of 92.0–104.3%as obtained for DA, and the R.S.D was 2.7–4.2%, so the proposedethod could be applied to the sensitive determination of DA in

eal biological samples with satisfactory results.

. Conclusion

In this work, we developed a simple and sensitive electro-hemical sensing method for convenient detection of DA in

rine samples through integrating MoS2–PANI composites anduNPs signal amplification. MoS2–PANI composites, the novel

unctional nanosheets, were fabricated and employed to preparehe AuNPs/MoS2–PANI film possessed good conductivity and

s of DA (a–k): 1, 3, 7, 12, 20, 70, 120, 200, 300, 400, 500 �M; (B). The plots of therations of DA and uric acid at AuNPs/MoS2-PANI/GCE in 0.1 M PBS (pH 7.0), from a80, 600 �M for uric acid.

electrocatalytical activity. The proposed electrochemical sensorshowed relatively low detection limit, satisfactory selectivity,acceptable stability and reproducibility. Moreover, the proposedmethod had been demonstrated to be suitable for sensitive detec-tion of DA in the human urine sample. Therefore, this new sensingplatform could offer a strategy to enhance the electrochemical per-formance and be used as the material to construct sensitive sensorsfor determination of trace target molecules in complex matrix.

Acknowledgments

We thank the financial supports of the National Natural ScienceFoundation of China (U1304214) and Natural Science Foundationof Henan Province of China (132300410060).

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Biographies

Ke-Jing Huang received his PhD in 2006 from Wuhan University. Presently, he isan associate professor at Xinyang Normal University. His research interests includeelectrochemical analysis, electrochemical sensors and biosensors.

Ji-Zong Zhang is a graduate student at Xinyang Normal University. Her currentresearches include chemical and electrocatalytic materials.

Yu-Jie Liu is a graduate student at Xinyang Normal University. Her current

researches include molecular electrochemistry and electrochemical materials.

Ling-Ling Wang obtained her MS degree in chemistry from Shandong Normal Uni-versity, China. Currently, she worked as a professor in Xinyang Normal University.Her current scientific interests are chemical and electrocatalytic materials.