The Structural Modification Of Carbon Dots And Its Application In Optical Analysis

Carbon dots(CDs)are,a kind of novel ultrasmall carbon nanoparticles,have attracted intense attention due to its unique fluorescence properties,low toxicity,good biocompatibility and low cost.However,most of the current research has mainly concentrated on the fluorescence properties of CDs,and other properties of CDs are less developed,which limits their application in other fields.As a result,the development of novel preparation of CDs with excellent properties and how to make it applicable in more and more fields are quite important.On the other hand,surface modulation or elements doping CDs are practical way to effectively modify its structures and properties,and facilitate their applications.In this dissertation,we focus on catalysis of CDs for luminol chemiluminescence in the absence of added oxidant and effect of surface groups modulation and elements doping on catalytic activity and fluorescence of CDs,and develop the new optical analysis methods for the biomolecules detection.The main contents of the thesis are as follows:1.Introduction.The first chapter is the general introduction of CDs.We summarize the·properties,property adjusting and synthesis methods of CDs and place emphasis on their recent application in the field of fluorescent and catalysis.2.Carbon dots-initiated luminol chemiluminescence in the absence of added oxidant.This paper reports for the first time the chemiluminescence(CL)behavior of luminol in the absence of added oxidant with CDs as the catalyst.By means of CL spectra,UV-vis spectra,electron spin resonance spectra,Fourier transform infrared and X-ray photoelectron spectra,the possible CL reaction mechanism is proposed.The CL luminophor was still 3-aminophthalate,the CL enhancement of luminol system was supposed to originate from the intrinsic catalytic activity of CDs,which can efficiently catalyze the decomposition of dissolved oxygen to generate superoxide radical anion in luminol solution.Then,the resulting superoxide radical anion reacted with luminol to cause CL emission.Furthermore,the effects of size and surface states on the catalytic activity of CDs were investigated.The results suggested that the catalytic activity of CDs are mainly affected by the surface states,and the size of CDs display little influence on the catalytic activity of CDs.Therefore,the catalytic activity of CDs can be tuned by modulating functional groups on the surface of CDs,which sheds new light on the characteristic of CDs.3.Effects of surface groups on fluorescence and catalytic activity of grapheme quantum dots.In general the surface state will affect the properties of the grapheme quantum dots(GQD),however,the effects of the surface groups on the properties of GQD have not systematically understand and study.In this work we designed and synthesized three GQD containing different surface groups(GQD-COOH,GQD-OH,and GQD-NH2)and explored the effects of the different surface groups on fluorescence and catalytic activity of GQD.The experimental results showed that the difference of surface group electronegativity could be the important reasons for the fluorescence and catalytic properties changes of GQD.In addition,we develop a new method for uric acid based on the inhibitory effect of uric acid on the GQD-initiated luminol CL system.Under the optimum conditions,the concentration of uric acid in the range from 5.0 ×10-7?16 ×10-5 g mL-1 exhibited a linear relationship with the inhibitory CL intensity,with a linear equation Ig?I 0.911c + 8.44 and correlation coefficient r=0.9956.4.Green synthesis of N,S co-doped carbon dots with highly luminescent for rapid,sensitive and label-free detection of biothiols in human plasma.This paper for the fist time reports on a simple,economical,and green preparative strategy toward N,S co-doped water-soluble,fluorescent CDs by hydrothermal process using low cost wastes alfalfa and garlic as precursor without the assistance of any chemicals but only pure water.The obtained N,S co-doped CDs had a high quantum yield under the longer wavelength of about 10%,narrow and symmetric emission spectra,resistance to photobleaching,and excitation-dependent fluorescence behavior.This study provided new way for tuning luminescence of carbon-based fluorescent material.We further explore the use of such N,S-CDs as probes for the sensing of biothiols,which is based on Cu2+nduced fluorescence quenching of N,S-CDs and biothiols can effectively shelter the FL quenching due to their ability to remove Cu2+rom the surface of CDs.This sensing system is successfully applied for detecting biothiol in serum sample.