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Sensors and Actuators B 177 (2013) 826– 832

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators B: Chemical

journa l h o me pa ge: www.elsev ier .com/ locate /snb

ne-pot preparation of glucose biosensor based on polydopamine–grapheneomposite film modified enzyme electrode

hangqing Ruana, Wei Shia,∗, Hairong Jiangb, Yanan Suna,∗, Xin Liua, Xinyuan Zhanga,hou Suna, Lingfeng Daia, Dongtao Gea

Department of Biomaterials/Biomedical Engineering Research Center, College of Materials, Xiamen University, Xiamen 361005, ChinaCollege of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China

r t i c l e i n f o

rticle history:eceived 26 September 2012eceived in revised form6 November 2012ccepted 3 December 2012vailable online 10 December 2012

a b s t r a c t

A green, facile and low cost approach was developed to fabricate a glucose biosensor based onpolydopamine–graphene hybrid film modified glucose oxidase enzyme electrode. Dopamine, grapheneoxide and glucose oxidase were mixed and casted on Au electrode, and after electrochemicalprocessing, polydopamine, glucose oxidase and graphene modified electrode was obtained. The as-synthesized enzyme electrodes were characterized by scanning electron microscopy, transmission

eywords:olydopamineraphenelucose oxidaselucose biosensor

electron microscopy, Fourier transform infrared and X-ray diffraction spectra. The biosensor showed theexcellent amperometric biosensing performances, e.g., a high detection sensitivity (28.4 �A mM−1cm−2),a low limit of detection (0.1 �m), a short response periods (<4 s) and a low Michaelis–Menten constant(6.77 mM). This might be attributed to large surface-to-volume ratio and high conductivity of graphene,and good biocompatibility of polydopamine, which could enhance the enzyme absorption and promotedirect electron transfer between redox enzymes and the surface of electrodes.

. Introduction

Graphene (GN), a monolayer of sp2 hybridized carbon atomsacked into a dense honeycomb crystal structure [1], has attractedtrong scientific and technological interest in recent years [2–4]ecause of its remarkable characteristics such as low cost, high sur-ace area-to-volume ratio [5], good biocompatibility [6], excellentlectrical conductivity, electron mobility and flexibility [7]. Due tots 2D structure all the delocalized p-conjugated electrons are effec-ively available on the surface which makes its electronic structureery sensitive to the local chemical environment [8]. Thus, GN pro-ides an ideal platform to prepare electrochemical sensors andiosensors [8,9]. Accordingly in the past few years, increasing num-ers of researches in this field have been devoted to the hybrid ofN with polymer, oxide and metallic nanoparticles for fabricatingnzymatic and nonenzymatic sensors [9–11].

Dopamine (3,4-dihydroxyphenylethylamine) (DA), a cate-holamine neurotransmitter, plays an important physiological rolen mammalians. Recently, inspired by mussel adhesion protein,

queous solution of DA was discovered to self-polymerization atlkaline pH to oxidize into thin adherent polydopamine (PDA)lms, which can be coated on various inorganic and organic

∗ Corresponding authors. Tel.: +86 592 2188502; fax: +86 592 2188502.E-mail addresses: shiwei@xmu.edu.cn (W. Shi), sunyanan@xmu.edu.cn (Y. Sun).

925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2012.12.010

© 2012 Elsevier B.V. All rights reserved.

substrates [12–14]. In addition, the PDA film could also be formedby electrochemical oxidation as a biocompatible matrix to immobi-lize biomacromolecules [15,16]. This mussel-inspired biomimeticapproach seems to be simple, inexpensive, quick and ‘green’. More-over, the PDA with catechol functional groups can be used as across-linker reagent for the immobilization of biomolecules bythe thiols and amines via Michael addition or Schiff base reaction[14]. For example, Lee et al. immobilized trypsin onto a vari-ety of substrates, such as cellulose, titanium oxide, copper, andpolycarbonate, via mussel adhesive protein inspired PDA coatingswithout other cross-linker reagents [17]. Li et al. reported that theglucose oxidase (GOD) immobilized in the electrochemical oxida-tion of dopamine could well retain its bioactivity and possess a highbiological affinity to glucose [15]. A PDA-GOD-Lac-MWCNTs/Pt glu-cose amperometric biosensor with PDA as an adherent to GODbased on laccase enzyme-catalyzed polymerization exhibited highglucose-detection sensitivity [18]. However, to the best of ourknowledge, the biosensors based the hybrid of GN with PDA havenot been reported so far.

Herein, we developed a green, facile, and low cost approachto fabricate enzyme electrode based on GN and PDA for glucosedetection, which combined the merits of PDA (good adhesion and

biocompatibility), GN (huge surface area, fast electron transfer-ring rate and good biocompatibility) and GOD (high and selectiveactivity toward glucose). DA, graphene oxide (GPO) and GOD weremixed and casted on Au electrode, and after oxidizing the monomer

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A and electrochemical reduction of GPO, the PDA-GN hybridlm modified enzyme electrode was obtained. The as-synthesizednzyme electrodes exhibited the high detection sensitivity, lowimit of detection, short response periods, wide linear range andow Michaelis–Menten constant.

. Experimental

.1. Reagents and apparatus

Graphite power (sized less than 30 �m), H2SO4 (98%), K2S2O8,2O5, KMnO4, HCl (37%), H2O2 and d-glucose were purchasedrom Sinopharm Chemical Reagent Co., Ltd., (China). GOD (spe-ific activity at 25 ◦C: >100 U/mg) was purchased from BBI (Bioasic Inc., Canada). Dopamine hydrochloride (DA) was purchase

rom Sigma–Aldrich. A stock solution of d-glucose was preparedn PBS and allowed to mutarotate at room temperature for 24 hefore measurements. All other chemicals and reagents were useds received without further purification. The ultra-pure water18 M� cm) used to prepare all solutions in this study was obtainedrom a water purification system provided by Pen-Tung Sah MEMSesearch Center of Xiamen University.

The electrochemical experiments were performed with aHI660d electrochemical workstation (CHI, USA). All experimentsere carried out with a three-electrode system consisted of a mod-

fied Au electrode ( ̊ = 3 mm) as the working electrode, a platinumire as the auxiliary electrode, and a Ag/AgCl/3.0 M KCl as the ref-

rence electrode. Electrochemical impedance measurements wereerformed in a 0.1 M KCl solution containing 5 mM K3[Fe(CN)6] and

mM K4[Fe(CN)6] (1:1), and the results were plotted in the form ofomplex plane diagrams (Nyquist plots) with a frequency rangerom 0.01 Hz to 10 kHz. The amplitude of the applied sine waveotential was 5 mV, whereas the formal potential of the system was

he open current potential. The cyclic voltammogram (CV) exper-ments were carried out in a quiescent solution at 100 or 50 mV/sn an electrochemical cell filled with 3.0 mL of PBS. LEO-1530 scan-ing electron microscopy (SEM, Germany), JEM-2100 transmission

Scheme 1. Schematic illustration of PDA-GOD-

ors B 177 (2013) 826– 832 827

electron microscopy (TEM, Japan), Rigaku Ultima IV X-ray diffrac-tion (XRD, Japan) and Nicolet IR200 (FTIR, USA) were applied forcharacterizing the prepared samples.

2.2. Preparation of the PDA-GOD-GN film modified electrode

Graphite oxide (GO) was synthesized from graphite powderthrough the modified Hummers method as originally presented byKovtyukhova and colleagues [19,20]. The as-synthesized GO whichhad been purified to remove residual salts and acids was suspendedin 10 mM Tris–HCl (pH 8.5) to give a brown dispersion. Exfoli-ated GO was obtained by ultrasound of the GO dispersion, usinga Sonifier (KQ 5200DE, Kunshan, China). The obtained brown dis-persion was then subjected to 30 min of centrifugation at 9000 rpmto remove any unexfoliated GO and the large size GO using a cen-trifuge (Universal 320R, Hettich, German). Aqueous suspensions ofgraphene oxide (GPO) were collected and stored for further use.

The Au electrode was polished with 0.3 and 0.05 �m aluminapowders, rinsed thoroughly with deionized water between eachpolishing step and sequentially sonicated in acetone, ethanol, anddeionized water, and then dried at room temperature. GOD andDA were dispersed in the prepared GPO suspension with vortexto obtain a mixed solution of 0.05 mg/mL GPO, 5 mg/mL GOD and5 mg/mL DA. A 6 �L of the suspension was dropped onto the Auelectrode and dried in air. For electrochemical oxidation polymer-ization of DA monomer, the modified electrode was processed withthe CV oxide in pH 7.4 PBS [21] under the potential range of −0.5to 0.5 V at a scan rate of 50 mV/s. The modified Au electrode (PDA-GOD-GPO/Au electrode) was stored at 4 ◦C for further use.

The electrochemical reduction of GPO of the hybrid film on Auelectrode was performed on the CHI660d by CV in 10 mM pH 5.0PBS (K2HPO4/KH2PO4) [22] saturated with nitrogen gas under thepotential range of −1.5 to 0 V at a scan rate of 100 mV/s. Then

the PDA-GOD-GN/Au enzyme electrode was obtained. For compari-son, PDA-GOD/Au, PDA-GN/Au and GOD-GN/Au modified electrodewere also prepared though the similar process without adding GPO,GOD and DA respectively. The target electrode was stored at 4 ◦C in

GN modified enzyme electrode synthesis.

8 Actuators B 177 (2013) 826– 832

acs

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28 C. Ruan et al. / Sensors and

refrigerator under dry condition when not in use. The typical pro-edure of constructing the modified electrode was schematicallyhown in Scheme 1.

. Results and discussion

.1. Characterization of GPO and PDA-GOD-GN

The surface morphology of GPO, PDA-GOD-GPO and PDA-GOD-N was characterized by SEM and TEM as shown in Fig. 1. Fig. 1And B displays that GPO nanosheets are transparent and flake-ike with wrinkles that can benefit immobilizing more GOD andeing trapped by PDA. Fig. 1C and D demonstrates that GPOnd GN nanosheets (black) were dispersed evenly in polymerDA (gray). From Fig. 1D we also notice that there were lots ofmall holes in the film of PDA-GOD-GN, which may cause by theas bubbles generating [23] during the reduction processing ofDA-GOD-GPO.

Fig. 2 shows FT-IR spectra of graphite, GPO, GOD and PDA-OD-GN. The sample used in FT-IR was collected by polishing

he modified electrode with KBr to scrape the PDA-GOD-GN.he characteristic peaks of GPO appearing at 3400, 1728, 1622

nd 1052 cm−1 (curve b) can be assigned to the O H stretch-ng mode of intercalated water, the C O stretch of the carboxylicroup (�(carbonyl)), the C C skeletal vibrations of unoxidizedraphitic domains or contribution from the stretching deformation

Fig. 1. (A and B) The SEM and TEM images of GPO (inset: high-magnification TEM

Fig. 2. FTIR spectra of graphite (a), GPO (b), GOD (c), and PDA-GOD-GN (d).

vibration of intercalated water and C O stretch (�(epoxy oralkoxy)), respectively [22,24,25]. The peak disappeared at 1728,1622 and 1052 cm−1 in PDA-GOD-GN (curve d) compared to FT-

IR spectrum of GPO was due to the reduction of GPO via CV. Whendopamine polymerizes, there is a few intense absorption featurearound 3423 cm−1 from catechol OH group in Fig. 2d [26]. This

image of GPO). (C and D) SEM images of PDA-GOD-GPO and PDA-GOD-GN.

C. Ruan et al. / Sensors and Actuators B 177 (2013) 826– 832 829

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stca[at

atdtag[totrt

3

feNaclprNiFIcet.Ptt

Fig. 4. Nyquist plot of EIS for bare Au electrode (a), PDA-GOD-GN/Au electrode (b),

ig. 3. The XRD patterns of pristine graphite (a), GO (b) and PDA-GOD-GN (c).

tructural feature supports the wrapping of GN by PDA. The spec-ra for pure GOD (curve c) is characterized by two absorption bandsentered at 1606 and 1543 cm−1 which are the typical amide Ind amide II absorption bands of protein molecules, respectively27,28]. After being wrapped into the PDA-GOD-GN, the amide Ind amide II peaks of GOD were observed in curve d, confirminghat the GOD was effectively immobilized by PDA film.

XRD patterns of the pristine graphite, GO, and PDA-GOD-GNre recorded in Fig. 3. Pristine graphite exhibits a sharp diffrac-ion peak at 2� = 26.5◦ (curve a) corresponding to a layer-to-layeristance of 0.336 nm according to Bragg’s law. Compared withhe pristine graphite, the feature diffraction peak of GO (curve b)ppears at 10.01◦ (0 0 2) as the AB stacking order is still observed inraphite oxide with layer-to-layer distance (d-spacing) of 0.892 nm22,25]. This value is larger than the d-spacing (0.336 nm) of pris-ine graphite (2� = 26.5◦) (curve a) as a result of the introductionf oxygenated functional groups on carbon sheets [22,29]. Afterhe composite of GPO in the PDA-GOD-GPO was electrochemicallyeduced, the peak located at 9.9◦ (curve c) disappeared, confirminghe reduction of GPO [22,30].

.2. Electrochemical impedance spectroscopy (EIS)

The electronic transfer properties of the electrodes after dif-erent surface modifications were characterized by EIS which wasmployed to monitor the modifying process of electrode [31]. Theyquist plot of impedance spectra includes a semicircle portionnd a linear portion. The semicircle portion at higher frequen-ies corresponds to the electron transfer limited process, and theinear portion at lower frequencies corresponds to the diffusionrocess. The electron transfer resistance of the electrochemicaleaction, Ret, which corresponds to the semicircle diameter of theyquist plot of −Z′′ against Z′, reveals the electron transfer kinet-

cs of the redox electrochemical probe at the electrode interface.ig. 4 displays EIS curves of the bare and modified Au electrodes.t can be seen from Fig. 4 that curve d is not an intact semicir-le, which suggests that Fe(CN)6

−4/3 redox couple has a very slowlectron transfer kinetics, possibly due to PDA-GOD film formed onhe electrode surface is insulating and hinds the electron transfer

The Ret values of PDA-GOD-GN/Au electrode (3114 �) andDA-GOD-GPO/Au electrode (309 k�) which are much smallerhan that of PDA-GOD/Au electrode (1321 k�) demonstrate thathe PDA-GOD-GPO, especially the PDA-GOD-GN which is the

PDA-GOD-GPO/Au electrode (c) and PDA-GOD/Au electrode (d) in the solution con-taining 0.1 M KCl and 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] (1:1). Inset: equivalent circuitused to model impedance data in the presence of redox couples.

product of the electrochemical reduction process of PDA-GOD-GPO, greatly improves the conductivity and the electron transferprocess.

3.3. Optimization of the biosensor

To obtain the good sensitivities and linear detection ranges forglucose assay, various conditions, including the concentration ofGOD, DA and GPO, casting volume, detection potential and pHvalues were investigated via variation of the examined one whileothers were fixed. We discovered that the biosensor showed max-imum response current at GPO, GOD and DA concentration of 5,5and 0.05 mg/mL, respectively. The cast volume of prepared PDA-GOD-GPO suspension was optimized as 6 �L.

The effect of the applied potential on the current response of thePDA-GOD-GN enzyme electrode was examined. Fig. 5A presentsthe dependence of the static current response to 1 mM glucoseon the applied potential varied from 0.3 to 0.8 V (vs. Ag/AgCl).The response increased when the applied potential was increased.Considering that interfering compounds can be oxidized at highapplied potential, we choose the applied potential of 0.7 V in ourexperiments. The pH value is another variable that affects the cur-rent response of the enzyme electrodes [32]. The pH dependence ofthe response of the PDA-GOD-GN/Au has been investigated and thecorresponding result was showed in Fig. 5B. The current increasedfrom pH 5.5 to 7.5, while decreased above pH 7.5. The maximumcurrent of the enzyme electrode was obtained at pH 7.5, due to theentrapment of GOD in the PDA film, which made GOD more activein neutral solution. From this figure, we also noticed that the pHbetween 7.0 and 8.0 has little effect on the current response of theenzyme electrodes. Since the pH of blood is about 7.4, pH 7.4 wasselected for glucose detection.

3.4. The performance of the PDA-GOD-GN modified enzymeelectrodes

Amperometric response of the PDA-GOD-GN/Au electrode tosuccessive addition of glucose in 0.1 M PBS (pH 7.4) was givenin Fig. 6A. For comparison, the determination of glucose usingPDA-GOD-GPO/Au, PDA-GOD/Au and GOD-GN/Au was also listed.At PDA-GOD-GN/Au electrode, as seen, rapid response and sharp

increase were observed when glucose was added to the PBS.The 95% of the steady-state current was obtained within 4 s.The corresponding calibration curves are presented in Fig. 6B.PDA-GOD-GN/Au electrode (curve a) gives a linear detection

830 C. Ruan et al. / Sensors and Actuators B 177 (2013) 826– 832

Fig. 5. (A) The static current response of PDA-GOD-GN/Au to 1 mM glucose in PBS (pH 7.4) at various potentials. (B) The static current response of PDA-GOD-GN/Au to 1 mMglucose in PBS of various pH at 0.7 V (vs. Ag/AgCl).

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ig. 6. (A) Amperometric responses of PDA-GOD-GN (a), PDA-GOD-GPO (b), PDA-pH 7.4). Applied potential: 0.70 V (vs. Ag/AgCl). Inset: one enlarged portion of the fOD-GN (d).

ange (LDR) of 0.001–4.7 mM, which is higher than that of PDA-Ox-Lac-MWCNTs/Pt (0.01–3.7 mM) [18]. The linear equation is

= 0.27632 + 2.00662 C, with a statistically significant correlationoefficient of 0.9972 and a slop of 28.4 �A mM−1 cm−2 (sensi-ivity), where I is in �A and concentration C in mM. The limitf detection is as low as 10−7 M (S/N = 3), which is obviouslyetter than that of GN–chitosan biosensor (2 × 10−5 M) [33],hitosan–Prussian blue–GN (10−5 M) [34], GN-ionic liquid biosen-or (10−6 M) [35], GN-Au-Nafion biosensor (5 × 10−6 M) [36] andDA-GOx-Lac-MWCNTs/Pt (5 × 10−7 M) [18]. The detail perfor-ance of detecting glucose of electrodes we prepared was listed in

able 1. By comparing PDA-GOD-GN/Au electrode with PDA-GOD-PO/Au, PDA-GOD/Au and GOD-GN/Au electrodes, we found that:

1) PDA can provide a suitable microenvironment for the enzymend GN; (2) the GN and GPO can promote the electron transferring

hich can enhance the performance of enzyme electrode; (3) the

lectrochemical reduction of GPO is essential to further enhancehe properties of the enzyme electrode.

able 1erformance of different electrodes for the determination of glucose.

Electrodes Sensitivity(�A mM−1 cm−2)

LDR (mM) LOD (�m)

PDA-GOD-GN 28.4 0.001–4.7 0.1PDA-GOD-GPO 20.8 0.001–2.5 0.1PDA-GOD 15.7 0.01–2.5 0.8GOD-GN 0.2 0.1–4.9 61

c), and GOD-GN (d) modified electrode with successive addition of glucose to PBSve. (B) Calibration curve of PDA-GOD-GN (a), PDA-GOD-GPO (b), PDA-GOD (c), and

3.5. Michaelis–Menten constant

The Michaelis–Menten constant (Km) can be calculated accord-ing to the Lineweaver–Burk equation [37]:

1ISS

= 1Imax

+ Km

Imax

1C

where, Iss, C and Imax stand for the steady-state current after glucoseaddition, the bulk concentration of substrate and the maximumcurrent measured under saturated glucose solution, respectively.The Km of the fabricated PDA-GOD-GN biosensor for glucose wascalculated according to data of curve a in Fig. 6A. The calculatedKm is about 6.1 mM. Although it is higher than the PDA-GOD-Lac-MWCNT modified electrode (4.1 mM) which used the moreeffectively laccase-catalyzed polymerization of DA, it is muchsmaller than the value obtained for the native GOD in solution(less than 27 mM) [38], the glucose biosensor based on single-walled carbon nanotube modified electrode (85 mM) [39], the Ptnanoparticles/mesoporous carbon matrix (10.8 mM) [40], the chi-tosan and Au nanoparticles modified electrode (10.5) [41] and the

boron doped carbon nanotube modified electrode (15.2 mM) [42].The smaller Km value indicates that the immobilized GOD possesseshigh enzymatic activity and the PDA-GOD-GN electrode exhibitsexcellent affinity for glucose.

C. Ruan et al. / Sensors and Actuat

Fig. 7. Time-dependent current responses at PDA-GOD-GN/Au to additions of 2 mMgA

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lucose, 0.1 mM AA, and 0.1 mM UA in PBS (pH 7.4). Applied potential: 0.70 V vs.g/AgCl.

.6. Interference, reproducibility and stability study

The selectivity and anti-interference ability were also examinedy chronoamperometric method. As shown in Fig. 7, the additionsf 0.1 mM ascorbic acid (AA) and 0.1 mM uric acid (UA) led to verymall responses, versus the large current increase after additionf 2 mM glucose. It was evident that the influence of interferingpecies tested on the glucose response was negligible, indicating

high selectivity of the PDA-GOD-GN biosensor. Ten repetitiveeasurements were carried out in 1 mM glucose and a relative

tandard deviation of 4.2% about the current was observed, whichndicated that the biosensor displayed an acceptable reproducibil-ty. The stability of the enzyme electrode was evaluated at 0.70 V toompare the amperometric current responses with a 10-day period.he biosensor was stored at 4 ◦C under dry conditions and detectedvery day in 1.0 mM glucose. The current response of the PDA-GOD-N enzyme Au electrode was approximately 90.1% of its originalalue, due to the good immobilization of GOD and GN by PDA. Inddition, the PDA film was found to be of cationic permselectivity16] and highly permeable to H2O2 [15] and thus the interferingurrents from the oxidation of anionic AA and UA may be notablyecreased at a PDA-modified electrode.

To demonstrate the sensor can be applied in clinical diagnos-ics, the as-synthesized PDA-GOD-GN Au electrodes were used toetermine glucose concentration of human blood serum. Serumample (0.5 mL) obtained from Zhongshan Hospital of Xiamen Uni-ersity (Xiamen, China) was added to 4 mL 0.1 M PBS (pH 7.4) asesting solution and a potential of 0.7 V was applied. The contentf glucose in blood was calculated from working curve. Each sam-le was performed for three times and the detection concentration

as the average of three detection results. As shown in Table 2,

he results obtained by the biosensor are in good agreement withospital-conducted blood test results on a commercial instrument.

able 2etermination of glucose in human blood serum samples.

Bloodserumsamples

Glucose concentrationmeasured by hospital(mM)

Glucose concentrationmeasured by PDA-GOD-GN/Au electrode (mM)

RSD (%)

1 3.52 3.48 2.62 3.68 3.88 3.43 4.12 3.98 2.9

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ors B 177 (2013) 826– 832 831

4. Conclusions

In this work, we developed a green, facile and low cost approachfor fabricating a new PDA-GN based enzyme biosensor. The as-synthesized PDA-GOD-GN biosensor exhibited the high responsesensitivity (28.4 �A mM−1 cm−2), fast response time (<4 s), andgood selectivity and stability. In this system, (1) the in situ solution-state immobilization GOD to GPO and reduction GPO simplified thepreparation process of biosensors; (2) PDA improved the activity ofthe immobilized GOD; (3) GN enhanced the electron transferringof PDA-GOD-GN. This one-pot electropolymerization and electro-chemical reduction may be applied in many other fields.

Acknowledgements

The authors acknowledge the support from the NationalNature Science Foundation of China (Nos. 81271689, 31271009,30500127), the Natural Science Foundation of Fujian Province ofChina (Nos. 2011J01331 and 2012J05066) and the FundamentalResearch Funds for the Central Universities (No. 2011121001).

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Biographies

Changqing Ruan is currently an M.Sc. student of the Department of Bioma-terials/Biomedical Engineering Research Center, College of Materials, XiamenUniversity. He received the B.S. degree from the Material Science and ChemistryEngineering College, China University of Geosciences in 2008 and now is mainlydevoted to the research of chemical sensors and functional nanomaterials.

Wei Shi is a full professor in the Department of Biomaterials/Biomedical Engineer-ing Research Center, College of Materials, Xiamen University. He received his Ph.D.in chemical engineering from Tianjing University in 2003. His research interestsinclude biosensors, membrane separation and biomaterials.

Hairong Jiang is an experimentalist of College of Chemistry and Chemical Engi-neering, Xiamen University. She obtained her B.S. from Jilin Institute of ChemicalEngineering. Her research interests include sensor and membrane separation.

Yanan Sun is an assistant professor of Biomedical Engineering, Department of Bio-materials/Biomedical Engineering Research Center, College of Materials, XiamenUniversity. She obtained her Ph.D. from Sun Yat-sen University in 2008. Her researchinterests cover biomaterials and biosensors.

Xin Liu is currently an M.Sc. student of the Department of Biomaterials/BiomedicalEngineering Research Center, College of Materials, Xiamen University. He receivedhis B.S. degree in Polymer Materials Science and Engineering from Zheng ZhouUniversity. His research interest is in area of membrane science.

Xinyuan Zhang is currently an M.Sc. student of the Department of Bioma-terials/Biomedical Engineering Research Center, College of Materials, XiamenUniversity. She received his B.S. degree from China University of Mining and Tech-nology. Her research interest is in area of drug delivery system and biomaterials.

Zhou Sun is currently an M.Sc student of the Department of Biomaterials/BiomedicalEngineering Research Center, College of Materials, Xiamen University. He receivedhis B.S. degree from Guangxi University. His research interest is in area of biomate-rials.

Lingfeng Dai is currently an M.Sc. student of the Department of Bioma-terials/Biomedical Engineering Research Center, College of Materials, XiamenUniversity. She received his B.S. degree from Huaqiao University. Her research inter-est is in area of conducting polymers.

Dongtao Ge is a full professor in the Department of Biomaterials/Biomedical Engi-neering Research Center, College of Materials, Xiamen University. He received hisPh.D. from Tianjing University. His research interests include conducting polymers,drug delivery system and biomaterials.