A micro-interdigitated array electrode-based microfluidic chip for the online detection of Hg(II)

Abstract

To meet the demand for rapid on-site detection of trace Hg2+ in aquatic environments, this paper presents an integrated microfluidic electrochemical sensor based on micro-electromechanical systems technology. The core component of the sensor is a Au-based micro-interdigitated array (MIDA) electrode, which utilizes the efficient pre-enrichment of Hg via underpotential deposition on Au surfaces to form Au–Hg amalgams, combined with the radial diffusion effect of microelectrodes. Finite element simulations were conducted to investigate the effects of electrode width and spacing-to-width ratio on the electrochemical characteristics and detection performance of the MIDA. The results indicate that smaller electrode widths and spacing-to-width ratios enhance radial diffusion and redox cycling, thereby enabling faster attainment of steady-state conditions and higher response currents. The preconcentration process of differential pulse anodic stripping voltammetry was optimized using an in situ flow enrichment strategy, thereby significantly enhancing detection sensitivity. The structurally optimized MIDA chip exhibited a linear detection range of 0.5 to 12 ppb, with a detection limit of 0.1 ppb (S/N=3), along with excellent repeatability (relative standard deviation<5.0%) and reproducibility. The sensor was applied to the analysis of tap water and lake water, achieving spike recoveries of 101.4%–107.8% and 94.0%–100.2%, respectively, thereby validating its reliability for monitoring Hg in real water samples.