Study Of The Synthesis Of Novel Nano Materials And Its Application In Biological Detection

Novel nanomaterials, such as metal nanoclusters, graphene, owning to their specialproperties have attracted much attention recently and have played important roles in biomedicaldetection. The analytical methods based on nanomaterials have been widely used in bioimaging,biosening, biolabeling, optical imaging, and so on, which possess many advantages includingsimple, fast, easy operation and high sensitivity. With the rapid development of relevantsubjects and the introduction of new techniques, the sensitivity, accuracy and selectivity offluorescence analysis and electrochemical methods increasingly improved and its applicationsrange many fields becoming an important and effective chemical analysis tools. This workprepared fluorescent gold/silver nanoclusters and constructed sensors based on nanometerialsfor sensing metal ions and small moleculars closely related to human health and safety. Inaddition, in consideration of the good fluorescent properties and biocompatibility of Au NCs,which were used as an ultrasmall fluorescent probe for in vivo and in vitro imaging. The maincontents and conclusions of this thesis are listed as follows: First of all, fluorescent gold/silver nanoclusters templated by DNA or oligonucleotideshave been widely reported, since DNA or oligonucleotides could be designed to position a fewmetal ions at close proximity prior to their reduction, but nucleoside-templated synthesis ismore challenging. In this work, a novel type of strategy taking cytidine as template to rapidsynthesis of fluorescent, water-soluble gold and silver nanoclusters （C-AuAg NCs） has beendeveloped. The characterizations demonstrate that C-AuAg NCs exhibited a intensive yellowfluorescence emission at 560 nm under 370 nm excitation, with a diameter of 1.50 ± 0.31 nm,a quantum yield ～9% and an average lifetime ～6.07 μs possess prominent fluorescenceproperties, good dispersibility and easy water solubility, indicating the promising application inbioanalysis and biomedical diagnosis. Furthermore, this strategy by rapid producing of highly;fluorescent nanoclusters could be explored for the possible recognition of some disease related changes in blood serum. This raises the possibility of their promising application in bioanalysis and biomedical diagnosis.Based on the excellent properties of Au NCs templated by cytidine, in this study, we have developed a label-free, dual functional detection strategy for highly selective and sensitive determination of aqueous Ag⁺ and Hg²⁺ by using cytidine stabilized Au NCs and AuAg NCs as fluorescent turn-on and turn off probes, respectively. The Au NCs and AuAg NCs showed a remarkably rapid response and high selectivity for Ag⁺ and Hg²⁺ over other metal ions, and relevant detection limit of Ag⁺ and Hg²⁺ is ca. 10 nM and 30 nM, respectively, importantly, the fluorescence enhanced Au NCs by doping Ag⁺ can be conveniently reusable for the detection of Hg²⁺ based on the corresponding fluorescence quenching. The sensing mechanism was based on the high-affinity metallophilic Hg²⁺-Ag⁺ interaction, which effectively quenched the fluorescence of AuAg NCs. Furthermore, these fluorescent nanoprobes could be readily applied to Ag⁺ and Hg²⁺ detection in environmental water samples, indicating their possibility to be utilized as a convenient, dual functional, rapid response, and label-free fluorescence sensor for related environmental and health monitoring.It is known that gold nanoclusters （Au NCs） with near infrared fluorescence possess outstanding physical and chemical attributes that make them excellent scaffolds for the construction of novel chemical sensors and biological imaging probe. In this study, a simple one-pot synthesis method, employing L-glutathione as the stabilizer and carbon monoxide （CO） as the reductant, was presented for preparation of fluorescent Au NCs. The as-prepared Au NCs exhibited a red fluorescence emission at 640 nm, with a diameter of 2 nm and a quantum yield ～7.6% . Firstly, based on the aggregation-induced fluorescence quenching mechanism, the Au NCs provided favorable biocompatibility, high sensitivity, good selectivity, and a limit of detection of 0.5 μM for the determination of ferric ion （Fe3+）. Furthermore, real samples （lake water and tap water） were analyzed for the iron contents using this proposed biocompatible fluorescent sensor, indicating the potential application in biological analysis. Secondly, the prepared Au NCs were applied for tumor-targeted imaging in vitro and in vivo due to its good photo-stability, strong fluorescence emission, excellent water solubility, and bio-compatibility. Furthermore, Au NCs combining with porphyrin derivatives were applied for photothermal;treatment to effectively inhibit the growth of tumors. This raises the possibility of Au NCs as a fluorescent probe for tumor-targeted rapid imaging and realize fluorescence imaging-guided photothermal therapy of tumors.In addition, the application of electrical signal is important as optical signal in biomedical detection. So we constructed a sensitive hydrogen peroxide （H₂O₂） sensor based on graphene-Pt （RGO-Pt） nanocomposites and used to measure the release of H₂O₂ from living cells. The graphene and Pt nanoparticles （Pt NPs） were modified on glassy carbon electrode （GCE） by the physical adsorption and electro-deposition of K₂PtCl₆ solution, respectively. Through characterization by scanning electron microscopy （SEM） and energy-dispersive X-ray spectroscopy （EDS）, it was observed that the electro-deposited Pt NPs were densely covered and well distributed on the entire graphene surface. Electrochemical study demonstrates that the RGO-Pt nanocomposites modified glassy carbon electrode exhibited a high peak current and low overpotential towards the reduction of H₂O₂. The relevant detection limit of H₂O₂ is ～0.2μM with a wide linear range from 0.5μM to 3.475 mM, displaying a much higher sensitivity （459 ± 3 mA M-1 cm-2, n = 5） than that of Pt nanoparticles or graphene modified electrode. This novel biosensor can measure the H₂O₂ release from living cells due to its low detection limit, wide linear range and higher sensitivity.In summary, this work prepared or assembled novel nanomaterials, based on their excellent properties employing fluorescence and electrochemical analysis as research strategy, realize the application in biomedical detection. This established an analysis method to realize quantitative detection based on photoelectric signal by means of metal nanoclusters fluorescence and electrochemical sensor response current. The application of metal nanoclusters in biological field make them to be a powerful tool for the study of macromolecules configuration, biological molecules interactions and to make cancer treatment more precise targeting.