Uncovering the Fundamental Properties of Multi-Scale Graphene Nanomaterials for Next-Generation Bioelectronics

The ability to manipulate the electrophysiology of electrically active cells and tissues has enabled a deeper understanding of healthy and diseased tissue states. This has primarily been achieved via input/output (I/O) bioelectronics that interface engineered materials with biological entities. Stable long-term application of conventional I/O bioelectronics advances as materials and processing techniques develop. Graphene is a unique 2D allotrope of carbon that has exceptional physical and chemical properties, and an enormous surface-area-to volume ratio. The dependence of the fundamental properties of graphene on its structure have been well studied. This has facilitated the development of graphene based I/O bioelectronics with a wide variety of functional characteristics. Further, to leverage the high surface-area of graphene, efforts have been made to synthesize complex three-dimensional (3D) geometries of graphene. Although various protocols have been developed to obtain 3D graphene nanostructures, the topology of the obtained graphene nanostructures is still limited. Additionally, the established relationships between the structure and fundamental properties of 2D graphene nanostructures cannot be directly extrapolated to the developed 3D nano architectures.

This thesis presents a truly 3D topology of graphene fabricated via templated synthesis of free-standing single-to-few-layer graphene flakes (nanowire templated 3D fuzzy graphene, NT-3DFG) for functional bioelectronics; and establishes the relationships between the material’s structure and its fundamental properties. The effects of the synthesis parameters on the hierarchical structure of NT-3DFG are mapped. The intricate 3D arrangement of free-standing graphene flakes leads high electrical conductivity via variable-range hopping dominated electron transport. In NT-3DFG, both basal planes and edges of the graphene flakes are electrochemically active and contribute to its high exposed surface-area. The enhanced electrochemical properties of NT-3DFG enable miniaturization of graphene-based microelectrodes to ultra-microelectrodes for functional bioelectronics. The 3D arrangement of graphene flakes confers high optical absorbance and downstream photothermal energy conversion. This enables remote nongenetic photothermal stimulation of 2D and 3D neuronal cultures with high spatiotemporal resolution using optical energies less than a hundred nanojoules. Uncovering the fundamental properties of multiscale graphene nanostructures demonstrates the importance of extending the nanomaterial topology to 3D.