4MBA-labeled Ag-nanorod aggregates coated with SiO2: synthesis, SERS activity, and biosensing applications

Abstract

A new nanostructure, silica-coated Ag nanorods (NRs) aggregate with 4-mercaptobenzoic acid molecules (4MBA-Ag NRs@SiO₂), was prepared by a seed-mediated growth method and a modified Stöber method. In the synthetic process, the optimal 4MBA-Ag NRs@SiO₂ was obtained by varying conditions such as surfactant concentration and centrifugation cycles. The morphologies and the optical properties of the 4MBA-Ag NRs@SiO₂ were investigated in detail by transmission electron microscope, UV-Vis spectrometer and Raman spectrometer. The experimental results show that the 4MBA-Ag NRs@SiO₂ prepared with 0.05 M CTAB has the aggregate morphology of single-crystalline Ag NRs, typical localized surface plasmon resonance (LSPR) characteristics and a high enhancement factor of surface-enhanced Raman scattering (SERS). Based on the SERS activity of 4MBA-Ag NRs@SiO₂ and Ag NRs, an immune probe and an immune substrate immobilized with anti-prostate specific antigen (anti-PSA) antibody have been fabricated and used to construct a sandwich structure for a PSA immunoassay; the detection limit of PSA reached 0.3 fg ml⁻¹. It is demonstrated that the as-prepared 4MBA-Ag NRs@SiO₂ has great potential in biosensing applications.