Preparation Of New Biomass Quantum Dots And Its Applications In Biosensing And Cells Imaging

Carbon quantum dots（CQDs）are also known as carbon dots（CDs）or carbon nano dots（CNDs）.CDs as a new type of carbon fluorescent nanomaterial have special optical,electrical,and chemical properties.CDs have a series of advantages such as low cytotoxicity,good biocompatibility,strong fluorescence,nano size（<10 nm）,high stability,good water solubility,easy modification,and are widely used in biosensing,drug delivery,bioimaging,electrocatalysis and other fields.Recently,researchers have continuously improved their innovation based on previous research.They have made breakthroughs in the preparation methods,mechanism analysis,optical properties,and potential applications of carbon quantum dots.However,the development of carbon quantum dots has not been more than a decade.There are still many problems that need to be resolved and further researches,such as the cumbersome preparation process;low quantum yield;single excitation single emission;fluorescence emission is currently in the blue region;applied research needs to be further expanded.Based on this,the natural biomass of sweet potato leaves,lettuces,and bok-choy were used as the green carbon sources.The high quantum yield of fluorescent CQDs（called as Biomass Quantum Dots,BQDs）was synthesized by hydrothermal method and solvothermal method,and the BQDs were applicated in biosensing and cell imaging with research and expansion.The details are summarized as follows:Part one:Nitrogen-doped fluorescent BQDs was synthesized in a one-step synthetic green raw material of hydrothermal（220°C,4 h）of natural biomass sweet potato leaves.This method is simple,low cost and environmentally friendly.BQDs is completely soluble in water and the solution emits intense blue fluorescence.Extreme p H and ionic strength are very stable and can be used as promising fluorescent sensors.Without further surface chemical modification,Hg²⁺can effectively quench the BQDs fluorescence.The fluorescence sensor system is designed to detect Hg²⁺with high sensitivity and selectivity.In addition,the prepared BQDs has been demonstrated to be useful for the determination of label-free imaging of Hg²⁺in environmental water samples and in living cells.Part two:One-step solvothermal method synthesis of near-infrared emission offluorescent BQDs by using biomass lettuces as the raw material.Using this BQDs as a probe,based on Inner Filter Effect,was established a simple and sensitive method to detectγ-glutamyl transpeptidase（GGT）and enzyme inhibitors.The method usesγ-L-Glutamyl-p-nitroanilide（GPNA）as a substrate,and GGT catalyzes the production of p-Nitroaniline（p-NA）by GPNA.The UV-visible absorption spectrum（maximum absorption wavelength of 405 nm）of P-NA overlaps with the fluorescence excitation spectrum（maximum excitation wavelength of 408 nm）of the synthesized BQDs,and the fluorescence of BQDs can be effectively quenched based on the Internal Filtration Effect.Therefore,the BQDs can be used as a GGT fluorescent nanoprobe.When the probe was used for GGT detection,the GGT concentration in the range of 0-10 U/L showed a good linear relationship with the fluorescence quenching rate of BQDs.The detection limit was 0.276 U/L,and the common metal ions,Amino acids,carbohydrates and other enzymes in the organism will not interfere the GGT detection.The method has been applied to near-infrared fluorescence imaging of GGT in Hep G2 cells.It shows that this method has the advantages of rapidity,simplicity,high sensitivity,good selectivity,etc.It has a broad application prospect in clinical diagnosis.Part three:One-step solvothermal method synthesis of single-excited,double-emission,near-infrared emission of fluorescent BQDs by using natural biomass bok-choy as raw material.The obtained BQDs were used to construct ratio fluorescent nanoprobes that were mediated by copper ions（Cu-BQDs）for the ratio fluorescence imaging of coenzyme A in living cells.This probe used the 488 nm emission peak as the reference signal and the 678 nm emission peak as the identification signal,when using ratio fluorescence detection of coenzyme A.This method could eliminate background fluorescent interference in biological tissues and greatly increase the accuracy and sensitivity of coenzyme A fluorescence imaging.when the Co A concentration was 0-75μmol/L,the Co A concentration and fluorescence intensity ratio(I₆₇₈/I₄₈₈)of the system showed a linear relationship and the detection limit was 40 nmol/L.This method has been applied to near-infrared ratio fluorescence imaging detection of live T24 intracellular Co A and the results was satisfied.