Electrochemical sensor for the detection of mercury in seawater using carbon dots–carboxymethyl chitosan hydrogel

The study aimed to develop a rapid electrochemical sensor for selective sensing of mercury ions in saline environments to ensure the safety of aquatic life and human consumption. A sulfopropyl methacrylate-based hydrogel composite, synthesised by incorporating carbon dot derived from fish skin and carboxy methyl chitosan (CMCS), was used as sensing probe for mercury in aquatic environments with varying salinity. The synthesized composite was formed by interacting the carbon dot with CMCS hydrogel through C–N, conjugated C=C double bonds, and carboxyl groups, as evidenced by Fourier transform infrared spectroscopy. Electrochemical sensing through cyclic voltammetry and electrochemical impedance spectroscopy of varied concentrations of Hg²⁺ exhibited excellent linear relationships between concentration and current/ real or imaginary impedance. The Hg²⁺ interacted with the amino, hydroxyl, and sulfhydryl groups of the hydrogel composite, leading to significant structural changes or bond shifts, which resulted in a strong current signal. An excellent sensing response was demonstrated at varied salinity levels, including natural seawater, as well as with the use of interdigitated electrodes. The sensor is capable of detecting low concentrations of mercury in water under varying salinity conditions, making it suitable for applications in marine and aquaculture environments.

Synthesis of carbon dot-carboxy methyl chitosan mercury sensor