Preparation Of Gold Nanoclusters And Their Application In L-cysteine,Folic Acid And Sodium Copper Chlorophyllin Analysis

Gold nanoclusters(AuNCs)have attracted increasing attention due to their facile preparation,good photostability,good biocompatibility,and easily functionalized with other biomolecules.AuNCs typically exhibits a core-shell structure complex consisting of core of a few to a hundred Au atoms and shell of ligand.Although a large number of ligands have been explored as the cappers to synthesize the fluorescent AuNCs with different optical properties for detection of drugs recently,the development of highly selective and sensitive detection method is still great challenge.Aiming at the above-mentioned problem,AuNCs were synthesized by regulating the charge density,type,and rigid structure of the ligands to significantly improve the selectivity and sensitivity of detection in this paper.Taking L-cysteine(L-Cys),folic acid(FA)and sodium copper chlorophyllin(SCC)as research objects,the research work is carried out:1)The fluorescence of gold nanoclusters protected by L-hydroxyproline(L-Hyp)could be quenched by AuNPs via the inner filter effect.After adding L-Cys to the AuNCs-AuNPs system,the quenched fluorescence of AuNCs was recovered due to the electrostatic and specific Au-S interactions between L-Cys and AuNPs.Due to the electrostatic,specific Au-S interactions and less steric hindrance,the proposed method based on the fluorescence "turn-off-on" strategy for L-Cys measurements could effectively avoid the interferences of S-containing amino acids(such as glutathione,homocysteine and methionine).The proposed method was successfully applied to the detection of L-Cys in human serum.2)AuNCs were synthesized with D-tryptophan(D-Trp)and its derivatives as the ligands.Due to the effect of ligand-shell rigidity and core-shell charge transfer,D-Trp@AuNCs produced higher fluorescence intensity and shorter fluorescence emission wavelength than the D-Trp-derivatives-ligands protected AuNCs.The high sensitivity and selectivity of D-Trp@AuNCs for detecting folic acid due to the static quenching and inner filter effect.The proposed assay was successfully utilized to determine the amount of folic acid in spiked human urine.3)Gold nanoclusters with strong red fluorescence at 633 nm were synthesized using bovine serum albumin(BSA)and bromelain(Bro)as dual ligands.The auto-fluorescence interference of the dual ligands was effectively avoided due to the fluorescence emission red-shifts of the prepared BSA/Bro@AuNCs;this may be mainly due to the rigid structure of the proteins.The BSA/Bro@AuNCs were highly selective to SCC based on the static quenching and inner filter effect.The proposed assay was further applied to the measurement of SCC in rat serums.