Silver deposited polystyrene (PS) microspheres for surface-enhanced Raman spectroscopic-encoding and rapid label-free detection of melamine in milk powder.

Silver nanoparticles coated amino modified polystyrene microspheres (PS-NH2/Ag NPs) with extremely high surface enhanced Raman scattering (SERS) activity and uniform surface morphology were created by precise controlling of deposition time. Nanojets that were formed underneath the individual microspheres could be used for nondestructive analysis of species adsorbed on the smooth gold or glass surface. A 10 fold enhancement of SERS was observed between PS-NH2/Ag NPs and gold surface compared to glass surface due to more effective coupling of surface plasmonic resonance. These microsphere SERS substrates could detect 2-Mercaptopyridine down to 10(-9)M. Four different thiol compounds have been successfully utilized as tags to prepare SERS encoded PS-NH2/Ag NPs microspheres. Furthermore, the potential application of these SERS substrate for rapid detection of melamine in milk powder was explored. A linear relationship was observed between SERS intensity and logarithm of melamine concentrations with the limit of detection (LOD) of 1.9 × 10(-8)mol/L. The promising advantages of easy sample pretreatment, low protein background interference, short detection time and low cost makes the PS-NH2/Ag NPs substrate a potential detection tool in the field of food safety.