The Application Of Graphene Quantum Dots In The Detection Of Biological Small Molecules

Fluorescence spectroscopy has been widely used in biomolecule detection owing to the advantages of low cost,operational simplicity,high sensitivity,rapid response rapid and etc.In order to detect and track target molecule,we must establish the relationship between target molecule and the fluorescent probe signal.As one of traditional fluorescent probes,fluorescent dyes suffer from photobleaching,narrow absorption band and short fluorescence lifetime,which limited its application in biological imaging and biomolecule detection.Quantum dots are not limited by these constraints but some key problems such as leakage of heavy metals and cytotoxicity caused by surface organic groups in traditional quantum dots still exist.Graphene quantum dots(GQDs)are considered to be competitive alternatives to organic dyes and heavy metal-based quantum dots and provide the possibility to solve the above problems because of its unique electrical and optical properties,including tunable photoluminescence,molecular size,excellent photostability,chemical inertness,good solubility,high biocompatibility,and ease of functionalization.In this paper,we developed fluorescent biosensors based on GQDs to detect the important biological small molecules in serum.In the first chapter,we described the properties,preparation methods and application of GQDs and introduced the research contents and significance of this paper.In the second chapter,we developed a novel turn-on fluorescent strategy for sensing ascorbic acid(AA)in serum based on the significant quenching effect of o-benzoquinone on GQDs.The phenolic hydroxyl of catechol could be oxidized to benzoquinone in the presence of hydroxyl radicals produced by hydrogen peroxide(H2O2)under the catalysis of horse radish peroxidase(HRP),resulting in fluorescence quenching of GQDs.As an effective antioxidant,AA with a g-lactone structure exhibits highly reducibility,which can easily remove H2O2 and free radicals.A part of the H2O2 and hydroxyl radicals could be consumed by AA,which can inhibit the generation of o-benzoquinone and resulting in fluorescence recovery.Thus,we can detect AA by monitoring the fluorescence intensity of system.In the third chapter,we constructed a simple and sensitive fluorescence sensor for the detection of glucose and uric acid based on different quenching effects of Fe3+ and Fe2+ on GQDs,which had potential application to detect metabolites associated with H2O2 release.In the presence of hydrogen peroxide,Fe2+ can be oxidized and converted to Fe3+,leading to more significant fluorescence quenching of GQDs.H2O2 can be produced by the enzymatic reaction of a series of metabolites,such as glucose and uric acid.In the presence of sufficient glucose oxidase or uricase,H2O2 generated was linearly correlated with the concentration of glucose or uric acid in certain range.Therefore,we can detect glucose and uric acid by monitoring the fluorescence intensity of system.In the fourth chapter,we established a sensitive and low-cost fluorescence sensor to detect dopamine and ascorbic acid based on the quenching effect of dopamine/Cu2+ complex on GQDs.Cu2+ has no significant effect on the fluorescence of GQDs.However,when dopamine was added to GQDs,the amino group-containing dopamine could be adsorbed on the surface of carboxyl-rich GQDs due to the electrostatic interaction and hydrogen bonding.Afterwards,when Cu2+ was introduced into the system,the catechol moiety of dopamine would be oxidized to o-semiquinone and complex with Cu2+ to form dopamine/Cu2+ complex,which led to significant fluorescence quenching of GQDs.However,when Cu2+ and AA were introduced into the system simultaneously,AA with strong reduction property could react with Cu2+ to disturb the generation of dopamine/Cu2+ complex containing o-semiquinone,resulting in the fluorescence recovery of GQDs.Based on the fluorescence intensity of system,we can detect dopamine and ascorbic acid with high sensitivity.