A New Near-infrared Fluorescent Probe-Synthesis Of Chiral Gold Nanoclustersand Their Cytotoxicity

As one of the most intensively investigatedmaterials with unique properties of both chiral molecule and gold nanoclusters,chiral gold nanoclusters have application in molecular detection,chiral catalysts,chiral recognition and many other areas.Developing new synthesis system of chiral gold clusters,especially the development of new methods which is characterized by high yield,monodispersity and without separation or purification has become one of the primary research of this area.Compared with other near-infrared fluorescent dyes,gold clusters have become a hot topic owing to their perfect properties including high molar absorption coefficient,high fluorescence quantum yield,strong ability to resist photobleaching and tunable emission spectra.The research and development of new NIRF chiral gold nanoclusters probes with favorable biocompatibility,high quantum yield,high stability and long-wavelength fluorescence emission band has been one of the frontiers in material science.NIRF chiral gold nanoclusters probewith favorable biocompatibility which combine the chiral recognition with near-infrared fluorescenceshow great potential applications in fluorescence detection and imaging.The main contents are listed as follows.1.We develop a NaOH-mediated NaBH₄ reductionmethod for the synthesis of monodispersity L-GSH-Au₂₅NCs,This method is facile,rapid,versatile and highly yield.The gold nanocluster was characterized by UV-Vis,TEM,FT-IR,CD,TGA,UV-VIS-NIR FS and many other test methods.The fluorescence emission peak is located in 930 nm with a big stocks shift（500nm）and wide scope of excitation.It is the only one known so far to have a so large fluorescence emission peak.We discuss the synthesis mechanism and near-infrared fluorescence properties.2.We develop an improved Brust method for the synthesis ofmonodispersity L/D-NIBC-Au₂₅NCs,This method is facile,rapid,versatile,highly yield and without separation.The gold nanocluster was characterized by UV-Vis,TEM,EDX,DLS,FT-IR,CD,TGA,UV-VIS-NIR FS and many other test methods.The more interesting and exciting findings were that both two chiral gold nanoclusters had a fluorescence emission peak in 918 nm with a big stocks shift（500nm）and wide scope of excitation,which implied that these chiral gold nanoclusters could be used as a new kind of near-infrared fluorescent probe.The fluorescence quantum yields of L-NIBC-AuNCs and D-NIBC-AuNCs were 6.9%and 8.2%,and exhibit higher photostability than the standard rhodamine 110.They were stable under the condition of wide pH range and different metal ions solutions.They are really nice near-infrared fluorescent dyes.3.Cell toxicity experiments by MTT colorimetric assayshow that both two kinds of chiral gold nanoclusters have no cytotoxicitywithin 48hoursundertheconditionthattheconcentrationofAuNCschangefrom1mg/Lto100mg/L.These findings provide an interesting insight that chiral gold nanoclusters can be used as a new kind of near-infrared fluorescent probe,which may lead to innovation in the near-infrared fluorescence（NIRF）imaging techniques.