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Title: Fluorescent quenching from functionalised graphene oxide films
Author: Li, Ruiheng
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2019
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Graphene has attracted lots of interest since the first discovery in 2004 and Chemical Vapor Deposition (CVD) is the most common method to create monolayer graphene films. Poly(methyl methacrylate) (PMMA) films are used to protect the graphene film to make the film mechanically robust enough for transfer and further handling. However, it is found that the removal of PMMA is hard, and any residual polymers remaining can affect graphene's properties. A combined study of Raman scattering, atomic force microscopy and neutron reflection can determine the amount and structure of remaining PMMA after the normal wash process. After the standard process of PMMA removal by acetone-IPA cleaning, we found the remaining PMMA film could be represented as a two-layer model: an inner layer with thickness of 17 Å and roughness of 3 Å mixed with graphene and an outer diffuse layer with an average thickness of 31 Å and a roughness of 4 Å well mixed with water. Based on this model analysis, it was demonstrated that the remaining PMMA still occupied a significant fraction of the graphene film surface. Consider the effect of the unavoidable impurities in graphene, the graphene oxide was used for the following experiments. Quenched Stochastic Optical Reconstruction Microscopy (qSTORM) was demonstrated with graphene oxide sheets, peptides and bacteria; a method of contrast enhancement with super-resolution fluorescence microscopy. Individual sheets of graphene oxide (GO) were imaged with a resolution of 16 nm using the quenching of fluorescence emission by GO via its large Resonant Energy Transfer (RET) efficiency. The method was then extended to image self-assembled peptide aggregates (resolution 19 nm) and live bacterial cells (resolution 55 nm, the capsular structure of E. coli from urinary tract infections) with extremely low backgrounds and high signal-to-noise contrasts (between one and two orders of magnitude contrast factor improvements that depended on the thickness of the graphene oxide layer used). The GO quenches the fluorescence across a thin layer at distances of less than 15 nm. Graphene oxide films coated with thin layers (<15 nm) of polystyrene, polymethylmethacrylate and polylysine are shown to be effective in producing high contrast qSTORM images, providing a convenient modulation of sample/substrate interactions. The GO film was found to expand in water and an antimicrobial peptide surfactants(G2C8) were combined with ultrathin (6 nm) graphene oxide (GO) films to form composite films. The volume of the absorbed peptide was comparable to the volume of the GO film. The films showed good stability in a liquid environment for at least 24 hours. Experiments with Staphylococcus aureus (ATCC 6538) shows an antimicrobial effect from the GO surface and 60% of the bacteria were killed by the peptide/GO composite surface within 20 minutes.
Supervisor: Lu, Jian Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available