Electrochemical impedance strategy for silicic acid detection in marine environments

Abstract

Silicic acid (H 4 SiO 4 ) is an essential macronutrient for silicifying phytoplankton, which contribute substantially to global primary production plays a key role in the oceanic carbon cycle. Reliable. The high-resolution monitoring of silicic acid is therefore important for understanding marine ecosystem dynamics and biogeochemical processes. Here we report a reagent-efficient impedimetric sensor for the selective determination of silicic acid based on electrochemical impedance spectroscopy (EIS). The sensing strategy is based on the formation of a silicomolybdate complex at the surface of a carbon paste electrode modified with ammonium molybdate and pre-treated under alkaline conditions to generate electroactive molybdate species. Measurements were performed under acidic conditions (pH 2.0), where the sensor exhibit linear response over a silicic acid concentration range of 0.5–300 µM, with a sensitivity of 46.07 Ω µM −1 (R 2 = 0.97) and a limit of detection of 0.42 µM. Repeatability was confirmed at low and high concentrations, with relative standard deviations below 8.1%. Selectivity was demonstrated in the presence of orthophosphate, where stable impedance responses were maintained and orthophosphate contributions were effectively excluded. Surface characterization by scanning electron microscopy and energy-dispersive X-ray spectroscopy supported the formation of molybdate − derived surface species and the selective capture of silicon at the electrode interface. The results demonstrate the potential of this impedimetric platform for sensitive and selective silicic acid detection while minimizing reagent consumption, making it suitable for autonomous, real-time monitoring in marine environment.