Dual-Modulated Heterojunctions for Anti-Interference Sensing of Heavy Metals in Seawater

Trace analyte detection in a complex environment such as in seawater is usually challenging for classic redox-based electrochemical sensors since the matrix effect of high salinity and various interfering species with similar redox properties can generate false positive/negative signals, thus impacting the sensitivity and specificity of the sensors. In this work, unlike redox-based approaches, we propose a novel sensing mode that relies on dual-modulated interfacial energy barriers of heterojunctions. By constructing the hierarchical structure of Ni/TiO₂/porous-reduced graphene oxide/chitosan (CS), we introduce interfacial energy barriers of Schottky junctions into the electrochemical sensors for Cu²⁺. Most importantly, we found that two factors, light and the electrostatic interactions between the heterojunctions and Cu²⁺, can be coupled to regulate the height of the interfacial energy barrier and at last exponentially magnify the sensing signals in response to Cu²⁺. Since the electrostatic interaction is inert to redox, the proposed sensor is robust against most interfering species even in seawater. Illumination further enhances its sensitivity by 6.23 times and endows it a limit of detection of 0.22 nM. Such a dual-modulated sensing mode is also valid in other heterojunctions such as in the p-n junctions of Ni/NiO/MoS₂/CS, demonstrating its potential in more universal applications.