High performance biological sensors based on organic electrochemical transistors (OECTs)

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High performance biological sensors based on organic electrochemical transistors (OECTs)


Author: Liao, Caizhi
Title: High performance biological sensors based on organic electrochemical transistors (OECTs)
Degree: M.Phil.
Year: 2014
Subject: Organic electronics.
Thin film transistors.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Physics
Pages: xix, 150 leaves : illustrations (some color) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2757535
URI: http://theses.lib.polyu.edu.hk/handle/200/7528
Abstract: Owing to its desirable properties, including flexible, solution-processable, low cost and versatility, organic thin film transistors (OTFTs) have emerged as a viable platform for high performance chemical and biological sensors. As an important type of OTFTs, organic electrochemical transistors (OECTs) have attracted a great deal of interest during the last few years, which could be attributed to its high stability in aqueous electrolytes and low operation voltage affordable for biological applications. OECTs based on PEDOT:PSS have shown extensive applications in chemical and biological sensors, including pH, bacteria, ions, glucose, dopamine, DNA, lactate, proteins, and cells, etc. In this thesis, the performance of OECT based glucose sensor has been systematically investigated. It was found that the sensitivity of OECT glucose sensor could be significantly improved by co-modifying gate electrodes with graphene nano-materials (graphene or reduced graphene oxide (rGO)) and the enzyme glucose oxidase. The low detection limit of the functionalized device to glucose was down to 10 nM, which was two orders of magnitude better than that of devices without graphene modification. The optimized devices showed a linear response to a wide range glucose concentration from 10 nM to 1 mM, covering the physiological glucose range in human saliva. In addition, the selectivity of OECT glucose sensors was systematically studied for the first time. The selectivity of OECT glucose sensors could be dramatically improved by modifying the gate electrodes with biocompatible polymers (Chitosan and Nafion). These modified polymers served as effective block layers to minimize the interfering effect from uric acid and L-ascorbic acid. Therefore, the sensitivity and selectivity of the OECT-based glucose sensors could be simultaneously improved by modifying gate electrodes.
High-performance OECT-based dopamine(DA) sensors have also been successfully fabricated. To improve the selectivity of DA sensor, the gate electrodes of OECT devices were modified with biocompatible polymers, such as Nafion and Chitosan. Additionally, the sensitivity of OECT based DA sensors could be further improved by the modification of graphene nanomaterials (graphene and reduced graphene oxide (rGO)) on the gate electrodes. The DA sensors functionalized with Nafion and graphene materials showed a detection limit down to 5 nM, and a wide linear region from 5 nM to 1 mM with a good selectivity. Therefore, the OECT-based DA sensors hold great potential for the disposable and low-cost sensing applications in the near future. In addition, OECT based uric acid (UA) sensors with high sensitivity and selectivity were successfully fabricated for the first time. The OECT UA sensors modified with enzyme (UOx), polyaniline (PANI) and graphene-based nano-materials (graphene sheets and reduced graphene oxide (rGO)) showed a high selectivity to UA additions. The sensors with UOx-rGO / PANI / graphene flakes / Pt gate electrode can detect UA down to 10 nM, which was approximately 4 orders of magnitude better than that of conventional electrochemical UA sensors using the similar enzyme electrodes. Interestingly, the devices demonstrated an excellent linear response in the range of 100 nM to 500 μM, covering the normal uric acid level in human body. Interference signals from co-existed bio-active intereferents (e.g. glucose, dopamine and ascorbic acid) were effectively blocked because of the modified polymer layers. Owing to the versatility of modification techniques, OECT devices can be further explored for various kinds of biological applications, including DNA, cells, bacteria, protein and antigen/antibody.

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