Synthesis of porous silicon based nanoparticles for applications in surface enhanced Raman spectroscopy

Abstract

In this work porous Si (PSi) nanoparticles (NPs) were prepared by magnesiothermic reduction of the synthesized SiO2 spheres, and Ag NPs were deposited on the PSi with formaldehyde or HF. In addition, silver NPs were deposited on the porous Si obtained by milling and etching the Si wafer. Silver NPs on SiO2 spheres and particles with Ag core and mesoporous SiO2 shell were also synthesized. SEM analysis showed the Ag NPs size distributions between 30.1 and 64.3 nm. The synthesized samples were quite stable in aqueous media and had zeta potential between −11.5 and −44.3 mV. The samples exhibited reversible physisorption isotherms of type II except for the sample with Ag core and SiO2 (Ag–S) coating, which exhibited a type IVa isotherm accompanied by the hysteresis characteristic of mesoporous adsorbents. The BET surface areas of the samples ranged from 9 to 56 m2g-1, with the mesoporous Ag–S sample having the largest surface area of 378 m2g-1. The surface enhanced Raman spectroscopy (SERS) performance of the synthesized samples was studied by analysing the detection limit of 4-mercaptophenylboronic acid (4-MPBA) as a probe molecule at 532 nm laser excitation. The lowest limit of detection of 1 × 10−5 mol dm−3 was obtained with the sample in which silver NPs were deposited on silica spheres (S–Ag).