"Turn-on" Type Fluorescent Sensor Based On Gold Nanoparticles

Gold nanoparticles possess larger absorption coefficient and a widerange of absorption and other significant optical properties in theUltraviolet-visible area, which can be used as the acceptor offluorophores （quencher）. Based on this, this thesis use goldnanoparticles as the quenching agent and chose proper donors in orderto establish three "Turn-on" type fluorescent sensors, and the method isconvenient, high sensitivity and so on. Specific content as follows:1. An efficient "Turn-on" type fluorescent sensor between organicfluorescence dye acridine orange （AO） as donor and gold nanoparticles asacceptor （quencher） was built. This system was used to determination ofbiothiols （Cysteine、Homocysteine、Glutathione）. AO is noncovalentlyself-adsorbed on AuNPs, which induces fluorescence quenching of AO asa result of FRET between AO and AuNPs. Upon on the addition ofbiothiols due to the strong interactions between the thiols and goldnanoparticles, which leads the dissociation of AO from the surfaces of AuNPs and thus its fluorescence "turn-on". Based on this, a novelspectrofluorimetric method was developed for the determination ofbiothiols. Under the optimum conditions, the linear range of threebiothiols are2.5-100nM,1-1.5nM, and75-950nM, respectively. Thedetection limit （3σ/k） of three biothiols are0.72nM,0.2nM, and1.0nM,respectively. The method can be used to determine the total thiols in samples with satisfactory results.2. A novel "Turn-on" type fluorescent sensor between core-shellnanoparticle, which possess good photostability （CdTe as core and silicaas shell were synthesized with st ber method） as donor and Aunanoparticles as acceptor （quencher） was investigated and based on this"Turn-on" system for determination of melamine. AuNPs arenoncovalently adsorbed on CdTe@SiO₂via electrostatic interaction,resulting in large fluorescence quenching due to FET betweenCdTe@SiO₂and the AuNPs. Upon addition of melamine, melaminemolecules can interact with AuNPs via covalent binding of theamino-group （NH2-） of melamine to the surface of AuNPs, which leads tothe dissociation of AuNPs from the surfaces of CdTe@SiO₂and thus thefluorescence of CdTe@SiO₂restore. Based on this, a new method wasdeveloped for the determination of melamine. Under the optimumconditions, the linear range is7.5-350nM. The detection limit ofmelamine is0.89nM.3. By using near-infrared dye BCB （Brilliant Cresyl Blue） as donor andGlutathione-modified gold nanoparticles as acceptor （quencher）. The new"Turn-on" method allow to the determination of amounts of Pb²⁺. In thebasic environment （pH=8）, the pkaof BCB is11.0, so the BCB havepositive charge and the Au nanoparticles have negative charge, AuNPsare noncovalently adsorbed on BCB via electrostatic interaction, resulting in fluorescence quenching due to FET between BCB and theAuNPs. Upon addition of Pb²⁺, GSH-modified gold nanoparticlesbecome aggregation due to the formation of chelating complex betweenPb（Ⅱ） and-COOH of the GSH, which leads the dissociation of BCBwhich interaction of Au nanoparticle from the surfaces of Aunanoparticle and thus the fluorescence of BCB restore. Based on this，anovel method was built for the determination of Pb（Ⅱ）. Under theoptimum conditions, the linear range is0.1¹0nM, The detection limit ofPb²⁺is0.041nM.