A double-spiral microelectrode chip for reagent-free detection of mercury(II) in seawater based on in-situ pH modulation

A double-spiral microelectrode sensor chip was developed for reagent-free detection of mercury ions (Hg(II)) in seawater via in-situ pH modulation. This sensor chip, fabricated with thin-film technology, employs double-spiral microelectrodes configuration where one spiral functions as the working electrode for Hg(II) detection, while the other serves as the pH-modulating electrode. By applying a constant voltage of 1.2 V to the pH-modulating electrode, water electrolysis was induced and a localized acidic microenvironment was established at the working electrode-solution interface. This approach effectively eliminated the need for the external strong acid reagents used in conventional detection methods. The experimental results demonstrate that the sensor achieved a linear detection range of 0.3–350 μg/L for reagent-free Hg(II) determination in simulated seawater samples, with a detection limit of 0.14 μg/L. The sensor also exhibited excellent repeatability, selectivity, and anti-interference capability. The recovery rates for Hg(II) detection in real seawater samples ranged between 93% and 109%. The integration of in-situ pH modulation into the double-spiral electrode paves the way for environmentally friendly, reagent-free sensors to monitor heavy metals in seawater.