High sensitivity optochemical and electrochemical metal ion sensor

A novel sensor that deploys opto- and electrochemical techniques for the rapid and highly sensitive separation and detection of metal ions in aqueous media is reported. The sensor comprises a porous membrane coated with an ultra-thin porous layer of highly ordered, hexagonally packed arrays of metal (Au and Pt) nanoparticles with ≤ 25 nm sub-gaps. This platform enables an integrated detection method that relies on in-situ surface enhanced Raman scattering. An additional scheme is utilised based on electrochemical impedance spectroscopy to increase both the selectivity and the sensitivity of the sensor. Electrochemical separation bolsters the effectiveness of the optical method through ion separation and pre-concentration. The latter are induced by forcing the liquid electrolyte through the membrane´s nanopores through a new proposed method based on surface tension mismatch. The sensor demonstrates high selectivity for six different heavy metal ions (Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Co²⁺, Ni²⁺) at concentrations that range from 1 to 20 ppb (1 × 10^-3-20 × 10^-3 μg/ml). The novelty of this sensor consists of the fact that the separation, pre-concentration and detection of the targeted ions are all performed in a single stage, eliminating the need for time-consuming and complex sample preparation steps.