Lin Peng，Dai Jiajia，Wang Hairui，Ke Shanming?，and Zeng Xierong?

1)College of Materials Science and Engineering，Shenzhen University，Shenzhen 518060，P.R.China

2)Shenzhen Key Laboratory of Special Functional Materials，Shenzhen Engineering Laboratory for Advanced Technology of Ceramics，Shenzhen 518060，P.R.China

Glucose sensors based on solution-gated graphene transistors

Lin Peng1，2，Dai Jiajia1，2，Wang Hairui1，2，Ke Shanming1，2?，and Zeng Xierong1，2?

1)College of Materials Science and Engineering，Shenzhen University，Shenzhen 518060，P.R.China

2)Shenzhen Key Laboratory of Special Functional Materials，Shenzhen Engineering Laboratory for Advanced Technology of Ceramics，Shenzhen 518060，P.R.China

A solution-gated graphene field effect transistor is used to develop a sensitive glucose sensor.The sensor can be used for the determination of glucose with a concentration of as low as 1×10-6mol/L without any nanomaterial modification for the Pt gate electrode.With some advantages like low-cost，easy fabrication，low working voltage，and good biocompatibility，this type of biosensor will be an excellent candidate for the applications of enzymatic sensing.

biosensor;graphene;glucose;solution-gated;field effect transistor;detection limit

Graphene has been widely investigated in recent years due to its excellent physical，chemical，mechanical，and electronic properties［1］.With a nanostructure of one-atom-thick and twodimensional carbon sheet，graphene exhibits many advantages like large specific surface area，remarkable electrical conductivity，excellent chemical stability，and good biocompatibility［2］.Therefore，graphene shows potential applications in chemical and biological sensors with high sensitivity，high selectivity，and prompt response time.More recently，graphenebased transistors have also been investigated for sensor applications.With some advantages like low operating voltage(less than 1 V)and solution stability，solution-gated graphene field effect transistors(SGGT)have been developed in bio-sensing，such as cell-based biosensor［3］，DNA sensor［4］，and bacteria sensor［5］.In this paper，we report a sensitive glucose sensor based on SGGT，in which glucose oxidase(GOx)is immobilized on platinum(Pt)gate electrode.The sensor can detect glucose concentration as low as 1×10-6mol/L even without any nanomaterial modification for the gate electrode.

1 Experiment

1.1 Device fabrication

Cr/Au source/drain electrodes were deposited on SiO2/Si substrate through a shadow mask with a thermal evaporator(Edwards Auto 306).The channel length and width of the devices were 0.2 mm and 6.0 mm，respectively.Then graphene film was transferred onto the source/drain electrodes.Finally，a poly(dimethylsiloxane)(PDMS)wall was attached to the SiO2/Si substrate to contain phosphate-buffered saline(PBS，100 mmol/L NaCland 10 mmol/L sodium phosphate，pH=7.0)during the electrical measurements，as shown in Fig.1.

Fig.1 (Color online)Schematic diagram of a SGGT fabricated on SiO2/Si substrate［7］圖1 制備在SiO2/Si襯度上的SGGT器件示意圖［7］

1.2 Gate electrode fabrication

GOx was dissolved in PBS solution with a concentration of 10 mg/mL.Then 20 μL GOx solution was drop-coated onto the surface of Pt gate electrode and dried at 4℃ for 12 h.Chitosan(CHIT)was dissolved in acetic acid solution with a concentration of 5 mg/mL.In order to improve the immobilization of GOx on Pt electrode，20 μL CHIT solution was then dropcoated onto the surface of GOx/Pt electrode and dried at 4℃for 12 h.After the CHIT film was formed，the CHIT/GOx/Pt electrode was rinsed thoroughly with de-ionized water and stored at 4 ℃ for future use.

1.3 Electrical measurements

The devices were characterized with a semiconductor parameter analyzer(Agilent 4156C).The PBS solution was used as an electrolyte.For transfer characteristics，the channel current IDSbetween source and drain was measured as a function of gate voltage UGunder a constant drain voltage UDS=-0.05 V.For sampling characteristics，IDSwas measured as a function of time under a constant drain voltage UDS=-0.05 V and a constant gate voltage UG=0.2 V.

2 Results and discussions

Fig.1 shows the schematic diagram of a SGGT fabricated on SiO2/Si substrate.The device is firstly characterized in PBS solution and bare Pt is selected as gate electrode.It can be found that the device shows very stable performance in PBS solution and the response time is less than 1 s.The transfer characteristic(IDS-UG，UDS=-0.05 V)of the device is shown in Fig.2.We can find that the conductance of the device exhibits ambipolar behavior when the gate voltage is applied within 1 V.The Dirac point of the transfer curve is at around 0.7 V.

Fig.2 Transfer characteristic of the device measured in PBS solution圖2 器件在PBS溶液中的U-I特性

Then SGGT device with CHIT/GOx/Pt electrode is used for glucose sensing.Fig.3 shows the channel current(IDS)as functions of time(UDS=-0.05 V，UG=0.2 V)when glucose with different concentration is added into PBS solution.We can find that IDSdecreases with the addition of glucose.The detection limit of the device for glucose is 1×10-6mol/L.A control experiment is conducted when using Pt gate electrode without immobilization of GOx.It can be found that there is nearly no change for the channel current when glucose with different concentration is added into PBS solution.Therefore，the determination of glucose by our device is attributed to the GOx on Pt gate electrode.

Fig.3 IDSas function of time when glucose with different concentration was added into PBS solution圖3 器件作為葡萄糖傳感器的電學(xué)特性

Here we discuss the mechanism of the glucose sensor behavior based on SGGT.The chemical reactions near the gate electrode are shown as follows:

D-glucose is catalyzed by GOx with producing H2O2and D-glucono-1，5-lactone.H2O2is then decomposed at the gate electrode，which leads to the electron transfer on the surface of the gate electrode.As a result，the effective gate voltage applied on the SGGT device changes，leading to the change of the channel current(IDS)of the device［6-8］.As SGGT has many advantages like low-cost， easy fabrication， low operating voltage，and good biocompatibility，it will be the excellent candidate for the applications in bio-sensing.

Conclusions

SGGT is exploited for the determination of glucose.The detection limit of the sensor is 1×10-6mol/L when Pt gate electrode without any nanomaterial modification is used.The sensor response is attributed to the decomposition of H2O2at Pt gate electrode.The detection limit of the sensor can be also improved by the modification of gate electrode with nanomaterials.Moreover，this type of biosensor shows potential applications in enzymatic sensing.

Acknowledgement:We thank professor Yan Feng from the Hong Kong Polytechnic University for his guidance in this work.

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基于電解質(zhì)門控石墨烯晶體管的葡萄糖傳感器

林 鵬1，2，戴佳佳1，2，王海瑞1，2，柯善明1，2，曾燮榕1，2

1)深圳大學(xué)材料學(xué)院，深圳 518060;2)深圳市特種功能材料重點實驗室，深圳陶瓷先進技術(shù)工程實驗室，深圳 518060

利用電解質(zhì)門控石墨烯場效應(yīng)晶體管制備了一種高靈敏的葡萄糖傳感器.即使不采用納米修飾的鉑金柵電極，這種傳感器對葡萄糖的檢測極限已可達到1×10-6mol/L.該器件具備成本低、易制備、工作電壓低及生物兼容性好等優(yōu)點，可廣泛用于酶生物傳感器的研究.

生物傳感器;石墨烯;葡萄糖;電解質(zhì)門控;場效應(yīng)晶體管;檢測極限

國家自然科學(xué)基金資助項目 (21405106，51272161)

林 鵬 (1982—)，男 (漢族)，福建省福清市人，深圳大學(xué)材料學(xué)院副教授、博士.E-mail:lin.peng@szu.edu.cn

/References:

Q 819

A

10.3724/SP.J.1249.2014.05452

2014-08-28;

2014-09-08

Foundation:National Natural Science Foundation of China(21405106，51272161)

?

Associate professor Ke Shanming，E-mail:smke@szu.edu.cn;Professor Zeng Xierong，E-mail:zengxier@szu.edu.cn.

:Lin Peng，Dai Jiajia，Wang Hairui，et al.Glucose sensors based on solution-gated graphene transistors ［J］.Journal of Shenzhen University Science and Engineering，2014，31(5):452-454.

引 文:林 鵬，戴佳佳，王海瑞，等.基于電解質(zhì)門控石墨烯晶體管的葡萄糖傳感器［J］.深圳大學(xué)學(xué)報理工版，2014，31(5):452-454.(英文版)

【中文責(zé)編:晨 兮;英文責(zé)編:新 谷】