Highly sensitive and selective determination of iodide and thiocyanate concentrations using surface-enhanced Raman scattering of starch-reduced gold nanoparticles.

In this report, we propose a novel technique for the determination of the concentrations of iodide and thiocyanate by surface-enhanced Raman scattering (SERS) of starch-reduced gold nanoparticles. Starch-reduced gold nanoparticles show an intrinsic Raman peak at 2125 cm(-1) due to the -C≡C- stretching mode of a synthesized byproduct. Because of the high adsorptivity of iodide on a gold surface, the intensity of the SERS peak at 2125 cm(-1) decreases with an increase in the iodide concentration. Thiocyanate also strongly adsorbs on a gold surface, and a new peak appears at around 2100 cm(-1), attributed to the -C≡N stretching vibration in a SERS spectrum of starch-reduced gold nanoparticles. These two peaks were successfully used to determine the iodide and thiocyanate concentrations separately, even in their mixture system. The detection limit of this technique for iodide is 0.01 μM with a measurement range of 0.01-2.0 μM, while the detection limit of this technique for thiocyanate is 0.05 μM with a measurement range of 0.05-50 μM. This technique is highly selective for iodide and thiocyanate ions without interference from other coexisting anions such as other halides, carbonate, and sulfate.