Solvent-induced Reversible Regulation Of Fluorescence Color Of Peptide-AuNCs And Mechanistic Research

The fluorescence regulation of AuNCs is mainly focused on the regulation of fluorescence intensity and color.Most of the fluorescence color modulation reported so far is unidirectional modulation,while the reversible modulation of fluorescence color for AuNCs is less studied.Therefore,it is important to synthesize AuNCs with high fluorescence intensity and controllable color,and to investigate their fluorescence conversion mechanism research.In this paper,from the perspective of peptide design,we use peptides as ligands to prepare AuNCs in aqueous solution,to modulate the fluorescence properties of AuNCs,and then to realize the reversible conversion of dual fluorescence,to provide new ideas for further design and development of color-controlled gold nanoclusters,which have potential development applications in the detection and imaging of living organisms.The specific research of this thesis is as follows:(1)Design of peptide sequence CCYGGYRFKYRFK.The peptide sequence consists of three parts: the gold cluster stable reduction region CCY,the flexible Linker region GG and the conformation-regulated region YRFKYRFK.Tyr in the stable reduction region of gold AuNCs provides reducing power under alkaline conditions,which allows Au(Ⅲ)to be reduced to Au(Ⅰ),while Cys forms Au-S bonds with Au(Ⅰ),and Tyr and Cys are prerequisites for the synthesis of AuNCs.The conformation-regulated region is composed of amino acids between hydrophilic and hydrophobic phases and aromatic rings,which can achieve conformational changes in hydrophilic or hydrophobic environments.The flexible Linker region is an intermediate linker region with a certain degree of flexibility,which allows the polypeptides on both sides to exercise their functions independently.(2)Preparation of highly fluorescent AuNCs in aqueous solution.Firstly,the AuNCs were synthesized in aqueous solution using self-designed peptides with both stabilizing and reducing properties,and the preparation conditions were optimized to obtain aqueous-phase AuNCs(H-AuNCs)with high fluorescence intensity.Secondly,the physicochemical properties of H-AuNCs were characterized by transmission electron microscopy(TEM),Fourier infrared(FTIR),X-ray photoelectron spectroscopy(XPS),steady-state transient fluorescence spectrometer,UV-Vis spectrophotometer and fluorescence spectrophotometer,and the analysis concluded that their high fluorescence intensity,small particle size and long lifetime can be used as fluorescent probes for bioimaging applications.Finally,the toxicity,uptake pathway and cell imaging of H-AuNCs uptake by HUVEC cells were characterized using enzyme standardization,flow cytometry and laser confocal imaging.(3)Reversible modulation of fluorescence color of AuNCs.The H-AuNCs solution was dried and its solid powder was transferred into DMSO to form the organic phase of AuNCs(D-AuNCs),and the fluorescence color changed from bright red to bright blue.Then aqueous solution was added to the D-AuNCs solution to form mixed-phase AuNCs(DH-AuNCs),and the fluorescence color was reversibly converted from bright blue to bright red.Characterization of D-AuNCs and DH-AuNCs and comparative analysis with H-AuNCs gold AuNCs revealed that the particle size and distribution,metal valence and content,and the number of surface peptides were the same for all three nano AuNCs,while the peptide structures and fluorescence lifetimes were different.It is hypothesized that the conformation and electron leap mode of the peptides change during the fluorescence color transition.(4)Study on the reversible color conversion mechanism of AuNCs fluorescence.The bright red fluorescence of AuNCs in aqueous solution is due to the fact that the hydrophilic amino group of the surface polypeptide is located outside and the terminal amino group is close to the gold nucleus,and the off-domain electrons of the amino group donate electrons to the gold nucleus directly,which belongs to the electron hopping from ligand to gold nucleus.π-π conjugation,which belongs to the electron leap between ligands;the gold nanoclusters in mixed solution possess both the above two fluorescence and electron transfer processes.