Preparation Of Gold And Silver Core-Shell Nanostructure And Their Localized Surface Plasmon Resonance For Sensing

Noble metal nanoparticles exhibit rich localized surface plasmon resonance properties, which is highly dependent on the composition, shape and size of metal nanoparticles. The dependence of their LSPR wavelengths on the surrounding refractive index is highly sensitive, which is extremely useful to prepare LSPR sensors. This kind of LSPR sensors is cheap, versatile, and yet sensitive.In this paper, we develop a simple and reproducible method to directly deposit Au core-Ag shell nanoparticles on ITO surface without any organic binder. Au@Ag nanoparticles at an average diameter of 80 nm were prepared by controlling deposition potential, deposition circles and the concentration of HAuCl4 and AgNO3. The Au@Ag nanoparticles on ITO substrate were characterized by means of UV-vis spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry (CV).The Au@Ag/ITO glasses were applied to development of refractive index sensors for variety of organic solvents. The sensitivity of 80 nm Au@Ag nanoparticles was 127 nm/RIU, which was about 76% higher than that of original gold nanoparticles.On the other hand, we deposited two different sizes of Ag@Au nanoparticles(60 and 100nm) onto ITO surface by regulating deposition potential, deposition circles and concentration of HAuCl4 and AgNO3. The Ag@Au nanoparticles on ITO substrate were characterized by means of UV-vis spectroscopy, SEM, CV and energy dispersive X-ray spectroscopy (EDS). Two different sizes of Ag@Au nanoparticles on ITO glass were used to investigate the response of different organic solvents. The sensitivities of Ag@Au nanoparticles at an average diameter of 60 and 100nm were 143 and 220nm/RIU, respectively. They were almost 80% higher than that of original silver nanoparticles. Then the analytical performances of sensor chips for monitoring both thiol and protein adsorption were examined. We chose the biotin-streptavidin system to validate the LSPR properties.Thirdly, we electrochemical deposited silver nanoclusters onto ITO glass surface. The silver nanoclusters on ITO substrate were characterized by means of UV-vis spectroscopy and SEM. We also investigated the optical properties of silver nanoclusters, such as the response of refractive index of various organic solvents, and a sensitivity of 148nm/RIU is obtained. After we deposited one layer of gold onto the silver nanoclusters, the sensitivity reached to 316nm/RIU. By systematically comparing the sensor activities of Ag nanoclusters and Ag@Au nanoclusters, we found that Ag@Au nanoclusters have higher sensitivity.