A facile microwave-assisted synthesis of Ag@SiO2 nanoparticles for Raman spectroscopy

Abstract

In the SERS community, new and simple ways of producing large diameter (above 50 nm) noble metal nanoparticles are highly welcomed because they shift the localized surface plasmon resonance to higher wavelengths where spectroscopic measurements are typically taken. In this work, we present a facile microwave-assisted synthesis of above average diameter silver-core silica-shell nanoparticles (Ag@SiO₂) using a chemical reduction method. Ag@SiO₂ were synthesized in two steps of the core synthesis and the shell capping procedure by stepped temperature ramping. UV/vis spectroscopy and HR-TEM imaging showed that core–shell nanoparticles are spherical with an average diameter of 90 nm ± 10 nm and are covered with a 2.5–3 nm thick silica shell. Particles were tested using Raman measurements of a 4-mercaptobenzoic acid monolayer. The proposed synthesis approach produces stable core–shell nanoparticles that can be stored at 8–10 °C in the dark for two months with only minimal indication of decay.