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

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