A New Sensor for Heavy Metals Detection in Aqueous Media

A novel technique for rapid and ultrahigh sensing of heavy metals in aqueous media based on microfluidic platform integrated with porous anodic alumina (PAA) membrane and functionalized with ultrathin porous layer of highly ordered hexagonal arrays of Au nanoparticles with 25 nm sub-gaps is proposed. The sensor function is based on both chemical and electromagnetic enhancement. Both were achieved by increasing the number of hot spots and by increasing the density of the Au-nanoparticles at the surface of the PAA membrane up to 7 × 10¹⁰ cm^-2. The sensor demonstrated high selectivity between three different heavy metal ions ( Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Co²⁺, and Ni²⁺) with concentrations varied from 1 to 20 ppb (1 × 10^-3 to 20 × 10^-3 μg/ml). The platform provides an instant and fully integrated detection method that is based on in-situ surface-enhanced Raman scattering (SERS) spectroscopy. The observed Raman enhancement is due to the excitation and interference of surface plasmon waves, which are highly dependent on the type and concentration of the heavy metal. Therefore, the proposed sensor is an unprecedented fully integrated platform that is easy to fabricate and seamlessly integrated with an in-situ signal detection device for added functionality.