Interfaces of Graphene and Biological Systems: Applications in Biomedicine and Energy

Interfacing of graphene (and other 2D materials) with biocomponents has led to its translation into a wide spectrum of applications in biotechnology, biomedicine and energy via development of a wide spectrum of novel bio-nanodevices. One of the ways to characterize graphene is using Raman spectroscopy which has shown to be a powerful tool to study materials. Although the electrical properties of graphene have been extensively studied for numerous applications including biosensing, research on graphene phononics to investigate nanobiointerface is limited. To gain insight in this field, we interfaced monolayer graphene with different cell systems - cancerous: Glioblastoma multiforme (GBM) cells and normal: Astrocytes, and investigated the interaction using Raman spectroscopy. The 2D Raman peak of graphene with GBM cells showed a large blue shift, ~6.3 cm-1, indicating a high degree of p-doping compared to when interfaced with astrocytes, ~2.3 cm-1. This is attributed to the different metabolic activity and surface chemistry among the two cell types. Such sensitive doping of graphene is attributed to its large quantum capacitance and the surface potential of the GBM cell was calculated to be ~310 mV. Following the cell study, we then investigated different cerebrospinal fluids (CSFs) obtained from patients with diseases affecting the central nervous system (CNS) including ALS, multiple sclerosis (MS) and other forms of motor neuron diseases (MND). The CSF with ALS n-doped the graphene lattice (red-shifted the 2D peak) to a different degree compared to other disease groups (MS and MND). Hence, the graphene-bio interface could potentially be used as a diagnostic tool for detecting ALS and to monitor the progression of ALS disease. We further investigated the utilization of the graphene- bio interfaces in other fields including bioenergy. Here, we interfaced graphene (reduced graphene oxide, rGO) with electrogenic bacteria (Geobacter sulferreducens) to understand the electron transport mechanism. In this study, the high conductivity and flexibility of graphenic sheets was leveraged. The interaction of bacteria with rGO led to addition of electrons (n-doping) (~5.3 cm-1) in the rGO lattice. This interface was also studied in a microbial fuel cell (MFC) like device, where the introduction of graphene in the anode chamber resulted in an estimated 2-fold higher rate of electron transfer. In addition, the interaction of graphene quantum dots (GQDs) with bacteria was characterized using Raman spectroscopy. In this study, we observed an enhancement in the bacterial peaks due to the presence of GQDs.