Investigations On The Preparation And The Peroxidase-like Activity Of Graphene Quantum Dots-copper Oxide Nanocomposites

Natural enzymes are a class of highly efficient biocatalyst,while their catalytic efficiency,activity and stability will be greatly reduced under industrial production conditions,which poses virtual influence on its large-scale practical applications.In recent years,great effort has been focusing on the development of artificial enzyme with higher stability and catalytic activity to replace the natural enzymes.In this paper,we focus on a kind of composites made from GQDs and CuO nanoparticles,study the preparation and the peroxidase-like activity of the composites and apply it to detect of H2O2 and glucose.In the first chapter,the recent advances on nanomaterial-based peroxidase mimics,including the varieties of nanomaterial-based peroxidase mimics,the methods for enzyme activity evaluation and the applications of nanomaterial-based peroxidase mimics in analytical chemistry are briefly reviewed.In the second chapter,GQDs are firstly prepared via one-pot microwave approach,and then GQDs/CuO nanocomposites are obtained via an chemical precipitation process by the in-situ growth of CuO nanoparticles on the surface of GQDs.The effect of the factors such as the preparation temperature,time,pH condition and the amount of source materials on the catalytic activity of GQDs/CuO nanocomposites are investigated and the optimal conditions are obtained.Various techniques including X-ray diffraction,X-ray photoelectron spectroscopy,Transmission electron microscopy,Atomic force microscopy,Infrared spectroscopy and Raman spectroscopy are adopted to characterize the composition,morphology,size and structural properties of the as-prepared GQDs/CuO nanocomposites.In the third chapter,the catalytic activities of GQDs/CuO nanocomposites as peroxidase mimics are systematically investigated.It is found that the as-prepared GQDs/CuO nanocomposites display excellent peroxidase-like activity and it can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)in the presence of H2O2 to produce a blue-colored solution.The results of steady state kinetic analysis indicate that the catalytic behavior of GQDs/CuO nanocomposites is in accord with the typical Michaelis-Menten kinetic model and follows a ping-pong mechanism.The Michaelis-Menten constant shows that GQDs/CuO nanocomposites own higher affinity towards substrates than natural HRP.Studies on the mechanism of catalytic reaction suggest that the nature of peroxidase-like activity of GQDs/CuO nanocomposites originates from the generation of highly reactive ·OH radical group.Based on the peroxidase-like activity of GQDs/CuO nanocomposites,a colorimetric method for the detection of H2O2 and glucose is established.H2O2 could be accurately detected in the concentration range of 5×10-7-1×10-5 mol L-1,with a detection limit of 1.7×10-7 mol L-1.Glucose could be accurately detected in the concentration range of 2×10-6-1×10-4 mol L-1,with a detection limit of 5.9×10-7 mol L-1.This developed method is successfully applied to the determination of glucose contents in serum samples,and the determination results agree well with that provided by the Hospital.