Surface-enhanced hyper-Raman spectroscopy using optical trapping of silver nanoparticles for molecular detection in solution

Abstract

Optical trapping of silver nanoparticles dispersed with rhodamine 6G (R6G) and NaCl in water gives surface-enhanced hyper-Raman scattering (SEHRS) of R6G. In this paper we have measured the SEHRS spectrum in the R6G concentration range between 10−7 and 10−11 M. SEHRS intensity and signal-to-noise ratio show clear differences at the lower R6G concentrations than ~10−9 M, indicating that the number of R6G in a trapped silver aggregate approaches the single-molecule level. This trapping SEHRS technique is applied for the detection of lysozyme molecules labelled with tetramethylrhodamine dye.