Fluorescent Gold Nanoclusters And Photoluminescent Gold Complexes For Biosensing Applications

Gold nanoclusters typically consist of several to hundreds of gold atoms and they belong to the new generation of luminescent nanomaterials. Their unique structure and properties have attracted great interest. The size of gold nanoclusters with diameter less than 3 nm generally vary between a single atom and the gold nanoparticles. Although not very exact boundaries between gold nanoclusters and gold nanoparticles, we can still distinguish them from their optical properties. The scales of gold nanoclusters approach the Fermi wavelength, resulting in splitting into discrete states and demostrating molecule-like optical properties. In addition to molecule-like optical properties, fluorescent gold nanoclusters hold many other important characteristics, e.g. large surface-area-to-volume ratio, easy surface modification, and tunable emission wavelength. Compared with other luminescent materials, gold nanoclusters has many advantages, such as simple preparation, good water solubility, low toxicity, biocompatibility and so on. Therefore, the fluorescent gold nanoclusters have a wide potential application. At the same time, we also realize that the fluorescent gold nanoclusters still retain some drawbacks of traditional fluorescers, for example, aggregation induced quenching, limitting its application in bioimaging. Thus, based on better understanding of emssion mechanism of gold nanocluster, we need to explore new luminescent materials with more excellent properties。The main contents are as follows.Firstly, A simple method has been developed for the fabrication of a reusable, fluorescent, copper ion sensor; this was done by immobilizing BSAGNCs with polyelectrolyte complexes on glass slides. The following fluorescent studies indicated that the fluorescence of the sensor could be effectively quenched by copper ion and be effectively recovered by EDTA, and this process could be repeated for at least 15 cycles. This suggested that this copper ion sensor could be reusable. When the reusable fluorescent copper ion sensor was applied to spiked tap water samples, the recovery of the added copper ion was found to be 96.3-99.6%. These demonstrations suggest a convenient approach for developing BSAGNCs-based, reusable fluorescence sensors.Secondly, In the present report we have unveiled the presence of the diTyr residues in the proteins used for synthezing GNCs by using the strategy of removal of the GNCs from the protein ligand cages. The formation of GNCs within the protein ligand cages indeed can alter the structural elements of the proteins, e.g., the breakdown disulfide bonds in proteins, which has been well-known, and the formation of diTyr cross-links unveiled in this study. It was also found that the GNCs@BSA are the system involving intrinsic FRET. In this system, the diTyr residues serve as a donor and the GNCs as an acceptor. Further investigation of GNCs@lysozyme and GNCs@ovalbumin systems led to the relatively general conclusion of the formation of diTyr in these GNCs@proteins systems and the presence of intrinsic FRET process.Thirdly, In this study, the CSH etching-induced fluorescence quenching of the BSAGNCs has been used to develop an etching-based method for label-free, separation-free, and selective sensing of CSH for the first time. CSH was found to exhibit powerful etching ability. CSH effectively etched the BSA-protected Au NC core, causing the fluorescence quenching. Other thiol-containing species in human blood serum such as Cys and GSH and other 19 natural amino acids did not interfere with the chemical etching by CSH. Under the optimal pH condition (pH 8.5), the linear range between the F/Fo and the concentrations of CSH was from 500 nM to 10,000 nM with a LOD of 150 nM (S/N=3). With the developed method, the deproteined human serum samples spiked with CSH were analyzed with satisfactory results.Lastly, we synthesized a novel photoluminescent gold complexs, through etching AuNCs@BSA with CSH. We first utilized a "top to down" strategy to synthsize this new luminescent materials. We conducted characteriszation and studies to obtain more information about this material. We found this matrials possess AIE properties. When introducing the aggregation inducer Cd2+,the compound of [Au4(SR)3]+ was obtained and confirmed. What’s more, the product was water soluble, showing promising applications in biosensor and bioimaging.