Optimization Of Luminescence Properties And Application Of Glutathione-protected Metal Nanoclusters

Metal nanoclusters(MNCs)is a new kind of luminescent nanomaterials,because of its special physical and chemical properties,such as long lifetimes,ultra-small size,large stokes shift,tunable luminescence,and good biocompatibility and photostability.Therefore,metal nanoclusters have been widely used in biosensing,bioimaging,analysis and detection.However,due to the low fluorescence quantum yield and poor stability of metal nanoclusters,the further application of metal nanoclusters is limited.To solve the above problems,the photoluminescence property of metal nanoclusters was optimized by other metal doping and aggregation induced emission enhancement methods.Firstly,glutathione(GSH)capped gold nanoclusters(AuNCs)were fabricated through a facile hydrothermal method.And we optimized the concentration of glutathione and sodium citrate as protective and reducing agent,reaction time and temperature,which showed an intense near-infrared(NIR)emission centered at 805nm.Furthermore,doping Ag(I)ions induced the fluorescence emission peak of Au NCs to shift from near infrared to red emission.When Ag(I)concentration is 0?20?M,a new emission peak at 615 nm appeared and the fluorescence is gradually enhanced with the increase of Ag(I)ions concentration.Meanwhile,the NIR emission is gradually quenched at 805 nm.Then,with the increase of Ag(I)ions concentration,the red emission at 615 nm gradually quenched,accompanied by emission redshift,and finally shifted to 720 nm when the concentration of Ag(I)ions reached to 120?M.The first stage of the luminescence enhancement at 615 nm was attributed to the anti-galvanic reduction(AGR)of Au NCs toward Ag(I)and surface deposition,which induced the formation of bimetallic gold and silver NCs(Au-Ag NCs).And the significant redshift was ascribed to the size growth and composition changes of the metal core.Besides,the luminescence emission of Au-Ag NCs could be enhanced significantly by introducing cysteine,which was attached to the surface of nanoclusters and increase the surface coverage.This study contributes to a deeper understanding of AGR of gold nanoclusters and provides a new way to control the composition,structure and photoluminescence properties of metal nanoclusters(NCs).Secondly,the glutathione-capped bimetallic copper and gold nanoclusters(Cu Au NCs@GSH)were achieved through gold doping into the unstable copper nanoclusters(Cu NCs@GSH),which induced the photoluminescence stabilization time increase from 4 to 7 days.Moreover,the Ce³⁺introduction further significantly increased the stable storage time(from 7 to 25 days)and the emission intensity(near140-fold),accompanying a quantum yields enhancement from 0.30%to 22%.It was observed by transmission electron microscopy(TEM)that the monodispersed Cu Au NCs@GSH formed larger particle assemblers(Cu Au NCs-Ce³⁺)under the induction of Ce³⁺,indicating that the fluorescence enhancement induced by Ce³⁺was due to the aggregation induced luminescence enhancement(AIEE)of nanoclusters.In addition,due to the strong interaction between adenosine triphosadenine(ATP)and Ce³⁺,Ce³⁺can be disassembled from the Cu Au NCs-Ce³⁺assembly to induce the dissociation of the assembly and the luminescence recovery of nanoclusters.Therefore,the Cu Au NCs-Ce³⁺assembly was applied to determine ATP.The results indicated that the linear detection range of ATP was 0?300?M,and the detection limit was 53n M.In addition,the method was successfully applied to determine ATP in diluted serum with very high recovery(98?104%).Therefore,the present study provides an efficient way to improve the fluorescence properties of metal nanoclusters and supplies a selective and sensitive ATP sensor.