A surface enhanced Raman scattering probe for highly selective and ultra sensitive detection of iodide in water and salt samples

Abstract

Iodine is a biophilic and essential trace element for all life and especially for vertebrates, which require it to produce indispensable thyroid hormones in their thyroid glands. As a result, the adequate measurement of iodine in water and food samples is crucial to lead a healthy life. Motivated by its importance, this is the first time in the literature that the highly selective and ultra sensitive (30 ppt limit) surface enhanced Raman scattering (SERS)-based detection of iodide ions (I⁻) from environmental and food samples has been reported. The desired sensitivity and selectivity has been achieved by measuring the change in the SERS intensity originating from Rh6G-adsorbed 30 nm gold nanoparticles (GNPs) upon the addition of I⁻. The strong chemical affinity offered by I⁻ towards the gold surface results in extra negative charge being deposited on it. As a result, the GNP surface attracts a greater number of positively charged Rh6G molecules and induces a marked increase in the number of hot spots through aggregation, providing a significant enhancement of the Raman signal intensity. The oxidation of I⁻ to molecular iodine (I₂) by hydrogen peroxide (H₂O₂) is employed for the successful screening of the bromide ion (Br⁻) which shows substantial interference at higher concentrations.