Microsphere-supported gold nanoparticles for SERS detection of malachite green

Abstract

Supported metal nanoparticles are attractive for wide ranging applications including catalysis and imaging. In this work we prepare surface-enhanced Raman scattering (SERS) active materials by exploiting the high surface area of porous carbon microspheres (CmP) to assemble high loadings of gold nanoparticles (AuNPs). The specific surface functionalization of CmPs is exploited to prepare composites by two approaches, (1) carboxylic acid surface groups are used to attract positively charged AuNPs and (2) a thiol functionalized surface is used to immobilize AuNPs. Ripening of the surface immobilized gold nanoparticles through hydroquinone treatment results in the preparation of a roughened gold surface with a 22-fold increase in the Au loading from 0.3 to 7.0 (mass Au/mass C). The materials were thoroughly characterized by UV-vis, Infrared and Raman spectroscopy, DLS, zeta potential, TEM and SEM. The SERS capacity of individual particles to detect malachite green, a mutagenic fungicide used in fish farming, was investigated using Raman optical tweezers. The challenges to trapping these materials due to the significant reflection, refraction and scattering properties of the Au-coated surfaces was overcome using a pinning approach. The measurements revealed the detection of malachite green at nM concentration and showed the potential of the porous carbon particles to act as versatile scaffolds for SERS applications.