Synthesis Of Gold Nanoparticles And Their Application In Localized Sufrace Piasmon Resonance Sensor

Gold nanoparticles exhibit well-defined optical properties on account of theirlocalized surface plasmon resonance (LSPR) phenomena and are developedrapidly and broadly. In aqueous solutions, gold nanoparticles exhibit strong plasmonbands that are depended on their geometric shape, size and the surrounding mediumconditions (such as dispersed in water, air or toluene). For spherical goldnanoparticles with diameters about20nm in water, a strong absorption band ataround520nm can be readily observed due to the excitation of plasmon by incidentlight. For gold nanorods, two LSPR bands could be observed, one associated withthe transverse mode (～520nm) and the other with the longitudinal mode (usually>600nm). The longitudinal plasmon wavelength is more sensitive to the changes inthe dielectric properties of the surroundings and the sensitivity increases with theaspect ratio of the nanorods. For the well-defined optical properties, goldnanoparticles have attracted much attention in many fields, such as optics, chemistry,bio-sensors, optoelectronic devices, biological analysis, and so on.The noble metal nanoparticles with different shape including gold nanorods,gold nanospheres and silver nanoplates were synthesized and used as the probes fordetermining Hg²⁺. Hg²⁺was reduced to Hg in the presence of sodium borohydride.Hg (0) can be bond on the surface of the nanoparticles to form a solid amalgam,which resulted in change of the size of NPs and caused the blue shift of theabsorption peak. Because NaBH4hydrolyzes in acidic condition, BR buffer solutionof pH10was selected to control the acidity of the sample solution. Gold nanorodsare positively charged due to the adsorption of the positively charged surfactantCTAB on the surface of the gold nanorods and high pH value can induce theaggregation of gold nanorods. Nonionic surfactants Tween20stabilized goldnanorods have good monodispersity at high pH value. Under the optimumconditions, when the gold nanorods are used, the shift in absorption peak of the longitudinal band is directly proportional to the concentration of Hg²⁺in the range of10.0-1500×10-9mol L^-1. When the gold nanospheres are used, the wavelengthshift is directly proportional to the concentration of Hg²⁺in the range of50.0-1000×10-8mol L^-1. When the silver nanoplates are used, the wavelength shift of thein-plane quadrupole resonance is directly proportional to the concentration of Hg²⁺in the range of20.0-500×10-8mol L^-1. The sensitivity obtained with goldnanorods is20and50times higher than that obtained with silver nanoplates andgold nanospheres, respectively. Gold nanorods were used as the probe to determineHg²⁺by spectrophotometry. Gold nanorods are aggregated in the presence ofdithiothreitol (DTT). However, the strong coordination of Hg²⁺with DTT results ina stable Hg–S covalent bond and inhibits the aggregation of the gold nanorods. Theaggregation level is related to the concentration of Hg²⁺. The absorbance ratio ismeasured with UV-vis spectrophotometer. Under the optimum conditions, theΔA780/A656is directly related to the concentration of Hg²⁺ranging from1.0to50.0nmol L^-1. The LSPR-based Hg²⁺sensor also shows excellent selectivity and theexperimental procedure is quite simple. The samples can be analyzed withoutprevious separation. This method can be applied for the determination of Hg²⁺inenvironmental samples.The purine compounds, such as adenine and guanine, are metabolites of nucleicacids and very important in the synthesis of DNA and RNA. The medicinescontaining purine compounds have been used to cure cancer. The anticancer drug6-thioguanine (6-TG) is one kind of purine compound and used to influence immuneresponse. The gold nanoparticles with different shape were synthesized, includinggold nanospheres and gold nanorods with different aspect ratio. A simple, rapidmethod for determination of6-TG based on the LSPR was described and theinteraction between gold nanoparticles and6-TG was investigated. The goldnanoparticles show their own LSPR bands in the UV-vis absorption spectrometry atcertain pH condition. After the addtion of6-TG,6-TG molecules can be stronglyadsorbed on the surface of AuNRs by–SH and induce the aggregation of goldnanoparticles, which alters the local refractive index in the vicinity of thenanoparticles and results in a shift of the LSPR spectrum. Under the optimalconditions, the ratios of absorbance at two wavelengths are directly proportional tothe concentrations of6-TG. The experimental results indicated that compared withgold nanospheres, when gold nanorods were applied, higher sensitivity and wider...