A Fiber-Structured Electrochemical Sensor for In Situ Monitoring of Metal Oxide Colloids in Riparian Zones

The degree of hydroxylation and the valence state distribution of metal oxide colloids determine the density of surface active sites and the interfacial charge characteristics. These properties directly influence the adsorption and enrichment behavior of pollutants, thereby contributing to changes of microbial activity in riparian zones and to global issues such as water eutrophication. However, existing analytical techniques for metal oxide colloids, including Raman spectroscopy and inductively coupled plasma mass spectrometry, remain limited in terms of anti-interference capability, trace-level detection, and discrimination of active species. In response to these limitations, this study proposes a construction strategy for a flexible fiber-based electrochemical sensor grounded in the principles of homogeneous adsorption and redox equilibrium of oxide colloids. The core concept involves using a conductive fiber as the substrate and employing a gel-based electrochemical synthesis method to construct a selectively oriented adsorption layer for active oxide sol species. Using this approach, selective detection of representative metal oxide colloids in riparian environments, including manganese, iron, and aluminum oxides, was achieved. Furthermore, the influence of ionic background, coexisting inorganic and organic sol systems, environmental temperature variation, and river flow conditions on sensor performance was systematically evaluated. With MnO₂ colloids as the representative target, the sensor achieved a detection limit as low as 0.016 mg/L. In addition, by integrating the sensor with a mobile boat platform, long-term dynamic monitoring in natural water bodies was successfully realized. Overall, this study provides a new technological approach for the in situ and selective monitoring of metal oxide colloids as highly reactive environmental media in riparian systems. It also offers a practical solution for the development of automated and continuous dynamic monitoring systems for natural aquatic environments.