Design of a peptide linker group to increase the surface enhanced Raman spectroscopy signal intensity of a rhodamine-nanoparticle system

The surface enhanced resonance Raman spectra of three modified carboxy-x-rhodamine dyes were recorded using Au nanoparticles and an excitation laser operating at 670 nm. The dyes were modified with a linker group designed both to increase the surface enhanced Raman spectroscopy signal and to couple the dye to the Au nanoparticles surface. The maximum signal intensity was recorded for a Cys-Gly linker with Cys thiol group acting as the coupling point to the Au surface and Gly-NH2 group used to attach the carboxy-x-rhodamine dye. This gave a signal intensity in the 1503 cm−1 Raman peak that was more than 20 times greater than for the unmodified dye. The Au nanoparticles used had a diameter of 49.8 ± 1.2 nm and were synthesised by the citrate reduction method.