Advanced Graphene Nanostructures for Biosensing Applications

Graphene is a sp2 hybridized carbon, arranged perfectly in a honeycomb structure to form a 2D monolayer of graphitic structure. It has become a popular choice in the development of electrochemical/electrical biosensor devices due to its large surface area, faster electron transfer kinetics, tunable band gap and ultrahigh charge carrier mobility with ballistic electron transport. The goal of this work is to synthesize advanced graphene nanostructures with improved electrical and physiochemical properties suitable for the development of ultrasensitive electrical/electrochemical biosensors. In the first project, seamless graphene-carbon nanotubes (G-CNT) hybrid film was synthesized using a two-step chemical vapor deposition (CVD) method where carbon nanotubes (CNTs) are grown on already grown graphene film on copper foil using iron as a catalyst. This three-dimensional G-CNT hybrid film has been studied for its potential in achieving direct electron transfer (DET) of glucose oxidase (GOx) and its bioelectrocatalytic activity in glucose detection. The DET between GOx and electrochemically oxidized G-CNT electrode was studied using cyclic voltammetry which showed a pair of well-defined and quasi-reversible redox peaks with a formal potential of – 459 mV at pH 7 corresponding to redox site of GOx. The constructed electrode detected glucose concentration over the clinically relevant range with the highest sensitivity compared to reported composite hybrid electrodes of graphene oxide and CNTs. G-CNT structure used in this work has potential to be used for development of artificial mediatorless redox enzymatic biosensors and biofuel cell. In the second project, an electrical transduction based biosensor platform for detection of biomolecular interaction using a graphene nanogap electrode has been developed. Different nanofabrication methods including focused ion beam milling (FIB), nanoidentation and E-Beam lithography (EBL) were studied in achieving reproducible planar nanogap electrodes of width less than 100 nm. Electrical biosensing concept was tested on nanogap electrodes using a high affinity interaction of streptavidin- biotin. Sensor performance was further optimized for achieving the high sensitive detection of streptavidin. The detection capability of this biosensor can be tuned down to the single to few molecules. Proposed biosensor platform can be used for any detection based on biomolecules affinity interaction such as for antigen-antibody or chemo-selective interaction with full potential to be used as a portable point-of-use biosensor