| Metal nanoclusters(NCs),so-called metal quantum clusters,have shown a series of fascinating features including low toxicity,extremely small size(? 2 nm),good biocompatibility,excellent chemical and photochemical stability,easy surface functionalization and so on.Nanoclusters have gained high interest in the field of nanomedicine for biosensing,imaging and biotherapy.Nanoclusters are commonly synthesized by rather simple methods using polymeric,small organic molecules or biological templates to stabilize them in solution.Metal nanoclusters are composed of a few to 100 atoms(usually gold or silver)and differed from nanoparticles as they exhibit molecular-like properties,long-lifetime fluorescence in the red-near-infrared region,and large two-photon excitation,which make them very suitable for in vitro and in vivo imaging.In principle,the fluorescence emission of NCs has been essentially attributed to a mixed effect of the charge transfer between the anchoring group of ligand and the NCs surface(ligand-to-metal charge transfer,LMCT)and quantum confinement in the metal core,which strongly depends on the intrinsic quantization effects of the metal core and the nature of ligand.Although metal nanoclusters have made great progress,there are still some problems,such as low fluorescence quantum yield and limitations in biological applications.Based on these properties of metal nanoclusters,We synthesized a series of metal nanoclusters and bimetallic nanoclusters using the new method,in order to improve its application in biology.And its luminescence mechanism and the bonding mode were studied deeply.Three parts are involved in thesis:(1).In the present study,the adenosine monophosphate(AMP)capped gold nanoclusters(Au NCs@AMP)are prepared by using a newly developed heating method.The reaction conditions such as time,temperature and concentration were optimized.Finally,1 h,80 ?C and AMP : Au = 10 : 1 were the best synthesis conditions,which show a strong and stable luminescence in a relative high QY(14.52%).The in-depth study by employing Infrared,1H and 31 P NMR spectra as well as Mass spectrometry supply possible binding model and ratio of AMP to the gold cluster,which have attributed the origination of such a high luminescence to both the binding of either purine ring and/or phosphate moiety of AMP as well as their orientations at the gold core surface.In addition,the electron-rich atoms as nitrogen and oxygen,or group moiety as-NH2 in ligands can largely promote the luminescence emission of the AuNCs.The present study reveal the intriguing generation of ultrabright luminescence from metal nanoclusters,and it will stimulate more researches both on the fabrication and practical applications of luminescent AuNCs.(2).Lactate dehydrogenase(LDH)is an enzyme commonly expressed in animals,plants and prokaryotes,and its main biological function is to catalyze the conversion between lactate and pyruvate as a proton transferase.An ultrabright adenosine monophosphate(AMP)capped gold nanoclusters(AuNCs@AMP)are used as a novel fluorescence probe to detect the lactate dehydrogenase(LDH),an important biomarker for common injuries and diseases.The fluorescence emission of AuNCs@AMP are quenched linearly in the presence of wide concentration range of LDH(50–1000 nM),covering the scope for clinical diagnosis.Particularly,the detection is very sensitive with an extremely low detection limit of 0.2 nM(26 pg/?L,0.8 U/L),being more sensitive than the previously reported ones.However,the proposed probe does not response to other commercial available proteins with different isoelectric points,which shows a high selectivity toward LDH.In addition,the response mechanism is also investigated in detail,where the quenching response is attributed to the binding of AuNCs to the free thiol groups at LDH surface.Therefore,the present study supplies a cost-effective,fast and easily performed approach to detect LDH with high selectivity and sensitivity,which provides a possible way for clinical diagnosis in future.(3).A novel gold-silver nanoclusters(Au/AgNCs@AMP)protected by AMP were designed.At the same time,the nanoclusters with uniform particle size were prepared by hydrothermal method.The optimum conditions for the synthesis of 120 ° C,30 min and AMP: Ag: Au = 5: 1: 0.2 were determined by optimizing the synthesis conditions such as temperature,time and concentration,and they had higher fluorescence quantum yield(QY = 8.46%).The Au/AgNCs@AMP were observed to be photosensitivity by fluorescence and ultraviolet absorption spectroscopy.Through the exploration of its preparation process,Au/AgNCs@AMP formed a structure with gold atoms as the core and silver atoms distributed on its surface.At last,we constructed the Au/Ag-AMP-PEI assembly system in order to furtherly improve its fluorescence quantum yield.Based on the dendritic structure of PEI and the strong binding ability of between –NH,-NH2 groups and metal atoms in PEI,Au/AgNCs@AMP is dispersed in PEI,which has a good drainage effect,and thus enhance QY about 4-fold(26.12%).In present study,Which provides a new synthetic method for small molecule-protected metal nanoclusters and hopes to provide a feasibility scheme for solving the problem of low quantum yield of NCs by constructing nanoclusters and macromolecule assembly systems. |
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