Fabrication Of Silver Nanoparticles In Ordered Two-Dimensional SiO₂ Cavity Array And The Application In Electrochemistry And SERS

In order to improve the sensibility, stability, and detection limit of bio electrochemical sensors, and to enhance the periodicity, stability, and repeatability of the substrate of SERS, two-dimensional highly ordered SiO₂ cavity arrays with different structures have been fabricated with silver nanoparticles（Ag NPs） located at the bottom of each cavity. In this case, we characterized the morphology, and researched the properties and application of the cavity array in electrochemical analysis and surface-enhanced Raman scattering（SERS） detection.Major research results are as follows:1. Two-dimensional array of SiO₂ cavities is fabricated on an indium-doped tin oxide（ITO） electrode by using monodispersed close-packed polystyrene（PS） spheres as a template. SiO₂ sol is infiltrated into the interstices among the PS spheres by centrifugation. After dissolving the PS spheres, the obtained two-dimensional ordered SiO₂ cavity array exactly reflected in the assembled array structure of the PS spheres. Then, silver nanoparticles（Ag NPs） are electrochemically deposited at the bottom of the SiO₂ cavity. Silver single crystal polyhedron dominated with（111） facets in each SiO₂ cavity are finally formed through adjusting conditions like calcination temperature and time to change the morphology of Ag NPs in the cavities. The two dimensional highly ordered SiO₂ cavity array with silver single crystal polyhedra（Ag（111）/SiO₂） exhibit excellent electrocatalytic activity toward oxidation of ascorbic acid. An electrochemical sensing platform of ascorbic acid is developed with high sensitivity, well stability, and low detection limit.2. Ag NPs, which are fabricated through reduction of silver nitrate by using sodium citrate as reducing agent, are self-assembled on the surface of glass slide. After that, highly ordered PS spheres are transferred onto the surface of Ag NPs and SiO₂ sol is filled into the interstices among the PS spheres by centrifugation. Two dimensional ordered SiO₂ cavity array with Ag NPs at the bottom（Ag NPs/SiO₂） is formed after removing the PS spheres. The as-prepared Ag NPs/SiO₂ can be used as a SERS active substrate. The array exhibit good reproducibility, stability, and repeatability of the surface enhancement by randomly recording 30 SERS spectra of 4-MBA molecules adsorbed at the Ag NPs/SiO₂ cavity array substrate.3. The surface of Ag NPs/SiO₂ was functionalized with modification of 1,3-propanesultone molecules（1,3-PS） and 3-Aminopropyltriethoxysilane（APTES）. Based on the electrostatic interaction mechanism, these two functionalized cavity arrays have charge selectivity to charged molecules. The wall of 1,3-PS/Ag NPs/SiO₂ cavity array is occupied by negatively charged sulfonic acid group, that would allow the passage of positively charged probe molecule but block the negatively charged probe. Vice versa, the positively charged amino group on the wall of the APTES/Ag NPs/SiO₂ cavities would impede the positively charged probe molecule but pass the negatively charged probe. SERS responses of 1,3-PS/Ag NPs/SiO₂ for methyl orange, methylene blue, congo red, and fuchsine solution are analyzed. It proves that the cavity arrays can be used as an excellent SERS active substrate with charge selectivity.