Biological Effects Of Functionalized Nanographene Oxide

Two dimensional graphene has attracted extensive interests in physics, devicefabrication, composites, energy, and biomedicine owing to its excellent physiochemical,electronic, mechanical and optical properties. These outstanding properties have madegraphene and its derivative graphene oxide (GO) potential candidates for biosensing,bioimaging, photothermal therapy, antibacterial agents, tissue engineering and asexcellent carriers for drugs (such as anti-tumor drug, photosentitiser) and gene delivery.This thesis intensively explored the interactions between different surfacefunctionalized graphene oxide (GO) and serum proteins, including complementcomponents, and then investigated the influence of surface functionalization ofgraphene oxide on the growth of microorganisms.In the first part, we explored interactions between serum proteins and twonanomaterials, GO and PEGylated GO (GO-PEG). The results showed that PEGylationcan markedly decrease the adsorption of proteins on GO. Interestingly, unlike GO,which adsorbs a number of serum proteins nonspecifically, GO-PEG exhibits reducedprotein binding in general and certain specificity towards a few proteins. Further massspectrometry (MS) identified these proteins are complement components, proteaseinhibitors and proteins related to coagulation.In the second part, we further investigated the interactions between complementsystem and two nanomaterials, GO and GO-PEG. It was found that PEGylation couldmarkedly decrease the complement activation by GO, and could also effectively alterthe interaction between C3and C3a, since compared to GO that bound to both C3a andC3with no apparent difference, GO-PEG exhibited little detectable binding to C3, butmuch stronger binding to C3a.In the third part, we studied the effects of different surface functionalization of GOon the growth of microorganisms. Interestingly, we found that polyethylene glycol(PEG) and polyethylenimine (PEI) dual functionalized GO (GO-PEG-PEI) could selectively inhibit the growth of S. aureus, while had no influence on E. coil andSaccharomyces cerevisiae. To our surprise, GO-PEG could significantly promote thegrowth of bacteria while showing no effect on yeast. Neither PEI nor PEG polymerthemselves had any effects on the growth of these microorganisms, demonstrating thatapparent alterations at the nano-bio interface after surface functionalization, whichchanged the surface chemistry, may result in altered the interaction of GO withdifferent bio-molecules and bio-organisms.