|Title:||Applications of graphene transistors in biological sensing|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xxvi, 145 leaves : illustrations ; 30 cm|
|Abstract:||Graphene, a carbon nanomaterial with a honeycomb 2D single atomic layer structure, has aroused great attention in scientific research since 2004.Due to its unique physical, chemical and electrical properties, graphene has been viewed as a potential candidate for many biomedical applications such as chemical and biological sensors.Among all kinds of graphene based sensors, solution-gated graphene transistor (SGGT) which can operate in electrolyte has been widely studied as promising candidate for high-performance sensors. SGGTs have several advantages over conventional methods, 1. The transistor-based structure of SGGT has both the sensing and the amplification functions, which implies higher sensitivity. 2. SGGTs can operate in aqueous environment with relatively low working voltages, which is important for many chemical and biological processes. 3. SGGTs are feasible for miniaturization and integration process because the device performance is dependent on the ratio of the channel width to length rather than device size.In this thesis, whole graphene solution-gated transistors with graphene as both channel and gate electrodes were fabricated and used as dopamine sensors. The limit of detection (LOD) of dopamine reached as low as 1 nM, which is three orders of magnitude better than that of conventional electrochemical measurements. The sensing mechanism is attributed to the change of effective gate voltage applied on the transistor induced by the electro-oxidation of dopamine at the graphene gate electrodes.The interference from glucose, uric acid (UA), and ascorbic acid (AA) on the dopamine sensor is characterized. In purpose of improving the selectivity of dopamine to the interferences, a thin Nafion film was modified on the graphene gate by solution process. After the modification, the device exhibited LOD of 1 nM to dopamine, 1 μM to AA and 10 μM to UA.|
Enzyme induced reactions on the gate electrodes of SGGTs could induce the change of effective gate voltage applied on the channel, and thus induce the variation of the conductance. Based on this mechanism, SGGTs with functionalized gate electrodes were designed and fabricated for hydrogen peroxide (H₂O₂) and glucose detection. Firstly, the graphene gate electrodes were modified by Pt nanoparticles through electrodeposition process. The sensitivity of the PtNP-modified SGGTs towards H₂O₂ could reach as low as 30 nM. Based on the as-prepared highly sensitive H2O2 sensor, glucose oxidase was immobilized on the gate electrode by using biocompatible polymers (Chitosan, Nafion). The LOD of the functionalized device towards glucose could reach as low as 0.5 μM. Due to the good biocompatibility and chemical stability of graphene, SGGTs were also developed as cellular interface platform in this thesis. Hepatocellular carcinoma epithelial cancer cell lines (HepG2), osteogenic cell lines (SAOS2), and fibroblast cell lines (HFF1) were cultured on the graphene channel of SGGTs, exhibited excellent biocompatibility. Cell activities on the SGGTs were monitored and analyzed during the adhesion process. The results indicated that the adherent cells could influence the electrical properties of SGGTs. Meanwhile, during the cell culture, constant electrical fields were applied on all the three electrodes of SGGTs, formed sequential Fermi level change on the SGGT channel. The corresponding distribution of different cell lines on the SGGTs was discussed.In summary, SGGT-based chemical sensors and biological sensors with specific functions were designed and fabricated.For many sensing applications,SGGTs performance biomedical detections.
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