Hg(II) Raman Sensor of Poly-L-Lysine Conformation Change on Gold Nanoparticles

In order to develop optical Hg(II) sensors, the adsorption characteristics of poly-L-lysine (PLL) after the conjugation of various ions on gold nanoparticles (AuNPs) were examined by means of Raman spectroscopy, UV-Vis absorption, and quasi-elastic light scattering (QELS). The intensities of the two bands at 458 and 1115 cm(-1) appeared to decrease, in comparison with that at 1150 cm(-1) in the presence of 100 mu M of Hg(II). The other ions of Cr3+, Pb2+, Mn2+, Zn2+, Co2+, Ni2+, Cd2+, Fe2+, Na+, K+, Ca2+, Mg2+, Cu2+, NH4+, and Fe3+ did not show such spectral changes. The prominent band at 1150 cm(-1), which may be ascribed to the C-N or gamma (NH3+) band, suggests that a conformational change of poly-L-lysine (PLL) occurs after its interaction with Hg(II) ions. The Hg(II) concentration-dependent SERS spectra indicated that the relative intensities of the two bands at 458 and 1115 cm(-1) decreased and that at 1150 cm(-1) increased above 1 mu M. These vibrational fingerprints may be useful to discriminate the Hg(II) ion above 1 mu M using AuNPs and Raman spectroscopy. On the basis of the presented spectroscopic study, we plan to develop an efficient method of detecting the Hg(II) ion at lower concentrations by introducing a variety of SERS platforms.