Synthesis Of Silver Nanoslusters And Gold Nanoclusters Stabilized With Reducing Templates And Their Applications In Pharmaceutical Analysis

Noble metal nanoclusters(NMNCs) are kinds of fluorescent molecular aggregates, consisting of several to tens of atoms. Among these NMNCs, silver nanoclusters(Ag NCs) and gold nanoclusters(Au NCs) have attracted increasing attention because of their stable fluorescent properties, tunable emission wavelengthes, and simple preparation procedure. Since Dickson’s group successfully synthesized fluorescent Ag NCs by using DNA and UV light as a template and reducing agent, respectively, more and more templates and methods were applied to synthesize Ag NCs and Au NCs for chemical sensing, bioimaging, and catalysis, et al. Although the current study on Au NCs and Ag NCs has been in-depth, there are some deficiencies in the synthesis and application of Ag NCs and Au NCs still remained to be overcome as following:(I) For the most of synthesis methods, it is necessary to introduce additional reducing agent or etching agent during the synthesis of Ag NCs and Au NCs, which is cumbersome and time-consuming;(II) As a novel fluorescence probe, Ag NCs and Au NCs are mainly confined to the analysis and bioimaging. The analysis is mainly based on direct “turn off” or “turn on”, which is sometimes unable to meet the requirements of sensitivity and selectivity. What’s more, the applications of Ag NCs and Au NCs in the environmental sensor has yet to be further expanded. Therefore, we carried out the following three works to resolve the existing problems in the synthesis and application of Ag NCs and Au NCs:1. A hydrothermal synthesis of orange fluorescent Ag NCs as a general probe for thiourea drugs was established by using PMAA as reducing agent and template. In this work, PMAA could reduce Ag+ to Ag0 and the fluorescent Ag NCs formed within 20 min under the heating condition(120 oC). The as-prepared PMAA-Ag NCs showed a maximum emission at 579 nm with a quantum yield of 5.38 %. The fluorescence of PMAA-Ag NCs could be quenched by thiourea drugs, suggesting PMAA-Ag NCs could be as a general probe for thiourea drugs. The fluorescence intensity of PMAA-Ag NCs decreased gradually and the colour of PMAA-Ag NCs solution darkened with the increase of thiourea drugs concentration. For the thiourea detection, the linearity over the range from 8.6 ?M to 2.3 m M could be fitted with(I0-I)/I0 = 0.07c-0.42. The limit detection was 6.1 ?M, which was close to its toxicity limit(76 ng/m L).2. One-step synthesis of temperature-sensitive fluorescent Ag NCs by using gelatin as reducing agent and template at room temperature. Gelatin is a kind of mixed polypeptide composed of eighteen kinds of amino acids, especially tyrosine and cysteine. The research result showed that gelatin could reduce Ag+ to form fluorescent Ag NCs with a maximum emission wavelength at 552 nm and quantum yield of 2.13 %. There were some advantages by using this method to synthesize Ag NCs as following:(1) One-step synthesis of gelatin-Ag NCs was established without any other extra reducing agent;(2) The preparation process was simple and time-saving, which could be finished at room temperature(25 oC) within 4 h. The fluorescence of gelatin-Ag NCs decreased with the increase of temperature. Therefore, gelatin-Ag NCs could be an indicator for the temperature. The decreased fluorescence emission at 552 nm of gelatin-Ag NCs showed a linear correlation with temperature over the range of 5 °C to 45 °C. The linearity could be fitted with I=-22.36 T(°C) +2064.55. The related coefficient r was 0.999. Furthermore, the result showed that the color of gelatin-Ag NCs solution changed from light yellow to brown with the increase of temperature and the absorbance of gelatin-Ag NCs at 425 nm showed a linear relationship with temperature over the range of 7 °C to 45 °C, indicating that the colorimetric monitoring of temperature also could be achieved.3. An off-on quantitative analysis of heparin was achieved based on the fluorescence resonance energy transfer(FRET) from BSA-Au NCs to aminofunctionalized graphene oxide(NH2-GO). The BSA-Au NCs containing amounts of carboxyl groups could be absorbed on the surface of NH2-GO through the electrostatic interaction, which resulted in the fluorescence quenching of BSA-Au NCs with high efficiency. However, heparin, possessing high density negative charge, could compete with BSA-Au NCs to bind NH2-GO and block the energy transfer from BSA-Au NCs to GO. In this work, NH2-GO was used to reduce the background fluorescence, which was benefit for the sensitivity. There was a good linear relationship fitted with I-I0=5.23 c Heparin+14.41 between fluorescence recovery of BSA-Au NCs and heparin over the range of 100 ng/m L to 30 ?g/m L. The detection limit was 40 ng/m L. What’s more, the established method was applied to the intracellular imaging of heparin in Hep-2 cells, providing the basis for the determination of heparin in mast cells.In summary, we have successfully synthesized fluorescent Ag NCs by using PMAA, gelatin as reducing agent and template. Subsequently, PMAA-Ag NCs, gelatinAg NCs, and BSA-Au NCs were used as probes for sulfur-containing drugs, temperature, and heparin, respectively. There were two innovations in this work:(1) Fluorescent Ag NCs were prepared only by using reducing templates, namely PMAA and gelatin;(2) The quantitive determination of heparin and temperature sensing were achieved by using BSA-Au NCs and gelatin-Ag NCs as fluorescence probes, broadening the applications of Ag NCs and Au NCs in analysis and environmental sensor.