Fully integrated battery-free and flexible electrochemical tag for on-demand wireless in situ monitoring of heavy metals

Migration of heavy metals from food contact materials to contained foods and drinks will cause severe health problems. The in situ analysis of the heavy metal ions inside these containers is in high demand. In this study, a fully integrated battery-free and flexible electrochemical tag is presented for wireless in situ detections of heavy metal ions in various containers. The circuit part of the tag is integrated with square wave anodic stripping voltammetry (SWASV) technique and near field communication (NFC) module, enabling on-board electrochemical sensing, wireless data transmission, and power harvesting. The circuits showed high consistency with commercial electrochemical workstation in SWASV analysis. A screen-printed flexible electrode array is connected with the circuit board. The working electrodes were modified with gold and bismuth nanoparticles respectively, which showed high sensitivity, selectivity, linearity, and reproducibility in the detections of lead and cadmium. The tag achieved quantitative detections of heavy metal ions in various containers, including enamelled cup, ceramic teapot, and dark-red enameled pottery. With proper encapsulation, the miniaturized passive and flexible tag can be attached to the inside surface of various containers for a long time. The wireless detections of heavy metal ions can be achieved just with an NFC-enabled smartphone outside the container. The platform provides a simple and effective solution for in situ analysis of toxic and harmful substances, which can be widely used in the areas of food safety and water quality monitoring.