A sensitive and selective Hg²⁺optical sensor has been developed based on the redox interaction of Hg²⁺with starch-coated silver nanoparticles (AgNPs) in the presence of 0.005 mol L⁻¹HNO₃. The relative intensity of the localized surface plasmon absorption band of AgNPs at 406 nm is linearly dependent on the concentration of Hg²⁺with positive slope for the concentration range 0–12.5 μg L⁻¹and negative slope for the concentration range 25–500 μg L⁻¹. Experiments performed demonstrated that metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Pb²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Fe³⁺, Co²⁺, and Ni²⁺) do not interfere under the same conditions, due to the absence of oxidative activity of these ions, which guarantees the high selectivity of the proposed optical sensor towards Hg²⁺. The limits of detection and quantification were found to be 0.9 µg L⁻¹and 2.7 µg L⁻¹, respectively, and relative standard deviations varied in the range 9–12% for Hg content from 0.9 to 12.5 μg L⁻¹and 5–9% for Hg levels from 25 to 500 μg L⁻¹. The method was validated by analysis of CRM Estuarine Water BCR505. A possible mechanism of interaction between AgNPs and Hg²⁺for both concentration ranges was proposed on the basis of UV-Vis, TEM, and SAED analyses.

Various types of nanomaterials such as magnetic nanoparticles, carbon nanostructures, metal oxides, noble metal nanoparticles, and ion imprinted polymers have been incorporated in new innovative approaches for speciation analysis.