Characterisation and Investigation of the Antimicrobial Properties of Graphene using Raman Spectroscopy

The need for antimicrobial materials is more prevalent than ever given the current antimicrobial resistance crisis. Graphene is an excellent material candidate for use as an antibacterial agent, in places where stopping the spread of bacteria is of the utmost importance, such as within healthcare establishments and on equipment used during operations due to its ability to kill microbes. The mechanism via which graphene causes cell death is, however, not fully understood. This project utilises Raman spectroscopy for investigation into the biomolecular interactions between Escherichia coli (E. coli) and graphene formed via chemical vapour deposition (CVD). Raman spectroscopy is a powerful tool for investigation into the metabolic state of microbes. Within this work Raman spectroscopy is also utilised for characterisation and analysis of three E. coli samples. Single point spectra and spectral averages at a population level display band variation pertaining to natural heterogeneity within biological samples, and due to different toxicity responses to desiccation and cell death. The level of characterisation of the samples is investigated through convergence of the statistical quantities, such as the standard error of the mean for increasing numbers of spectra in the average, to ensure full representation of the heterogeneity in the spectral average. Raman spectroscopy is also utilised for characterisation of CVD graphene, which uncovers significant levels of heterogeneity both within and across samples. Bands shifts of up to 28 cm-1 were recorded for bands in the Raman spectra of graphene, due to the presence of defects, such as grain boundaries and strain resultant from the CVD formation process. This level of heterogeneity could have serious repercussions for interactions of biological samples with graphene. Novel methods for determination of the level of characterisation and investigation of the level of heterogeneity are proposed within this work, with potential application to other systems.