Jianbo Sun

Date of Graduation

2018

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Yuxin Liu

Committee Member

Thirimachos Bourlai

Committee Member

Jeremy M. Dawson

Committee Member

Harry O. Finklea

Committee Member

Larry A. Hornak

Abstract

Biosensors are called upon to provide valuable benefits for human society in vital fields such as disease diagnosis, food inspection, environment monitoring, etc. Among the various biosensor architectures, the field effect transistor (FET) biosensors are promising as the next generation nanoelectronic biosensors, particularly attractive for point-of-care biomedical applications. The FET biosensors typically operate by measuring the conductance change of the semiconducting channel induced by the adsorption of the target biomolecules on it. The superior properties of graphene, including the unique electronic characteristics, facile functionalization and good biocompatibility, etc., make it an ideal building block for the FET biosensors. In this dissertation, we present studies on the electrolyte-gated graphene field effect transistor (EGGFET) biosensor and its application for the label-free detection of biomarkers. Poly(methyl methacrylate) (PMMA) residues have long been a critical challenge for the transfer of the chemical vapor deposited (CVD) graphene, which is critical to obtain reliable devices. To address this issue, we first studied the degradation of the PMMA residues upon thermal annealing using Raman spectroscopy. An electrolytic cleaning method is shown to be effective to remove these post-annealing residues, resulting in a clean, residue-free graphene surface. The performance of the EGGFET biosensor is demonstrated by the successful detection of human immunoglobulin G (IgG) using IgG-aptamer as the bioreceptor. The gate voltage with the minimum conductivity (𝑉Dirac) in the transfer curve of the EGGFET biosensor is used for the quantitative measurement of IgG concentration. In EGGFET biosensors, the graphene channels are directly exposed to the electrolytes, of which the composition, concentration and pH may vary during the testing. The response of the EGGFET biosensors is found to be susceptible to these variations which might lead to high uncertainty or even false results. We present an EGGFET immunoassay which allows well regulation over the matrix effect. The performance is demonstrated by the detection of human IgG from serum. The detection range of the EGGFET immunoassay for IgG detection is estimated to be around 2-50 nM with a coefficient of variation (CV) of less than 20%. The limit of detection (LOD) is around 0.7 nM. Different from the metal-oxide-semiconductor field effect transistors (MOSFET), the gate voltage is applied on the electrolyte and the electrical double layer (EDL) at the electrolyte-graphene interface serves as the gate dielectric in EGGFET. We studied the capacitance behavior of the electrolyte-graphene interface; the results suggest that the electrolyte-graphene interface exhibits a complex constant phase element (CPE) behavior (1 𝑍 = 𝑄0 (𝑗𝜔) 𝛼 ) with both 𝑄0 and 𝛼 varying as functions of the gate voltage. The EDL capacitance and the quantum capacitance are determined which allows us to extract the carrier density and mobility in graphene. This study give insight into the device physics of the EGGFET biosensor and is instructive for the design of the EGGFET biosensors on the device level.

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