Smartphone-based wearable microfluidic electrochemical sensor for on-site monitoring of copper ions in sweat without external driving

The directional movement of liquid without exogenous drive can show great potential in portable electrochemical platforms. Herein, we developed a portable electrochemical platform that drove electrolyte flow by surface tension gradient, which can realize collection of electrolyte, flow preconcentration and electrochemical detection of Cu2+. The induced graphene electrodes (LIG) was fabricated using laser direct writing, and flower cluster shaped ZnO nanorods (FC-ZnONRs) were prepared and modified on LIG, which provided a large amount of space for electrolyte to shuttled between the holes of LIG and ZnO, and increased the electrochemical active sites and electrons transport ability. The effect of surface tension gradients driving fluid flow could accelerate preconcentration, shorten detection time (save 300 s of preconcentration time) and enhance electrochemical responses in synergy with the 3D FC-ZnONRs/LIG. The microfluidic system possessed excellent performance for detection of Cu2+ ranged from 1 μg L−1 to 2100 μg L−1 with a low detection limit (LOD) of 0.0368 μg L−1 and high sensitivity of 0.414 μA (μg L−1)−1 cm−2. Additionally, this portable microfluidic system was successfully worn on the skin for analysing Cu2+ in human sweat, and the results showed good consistency with inductively coupled plasma-mass spectrometry (ICP-MS). This novel sensing system provides a sample collection, rapid detection, low cost and easy-to-operate strategy for heavy metal ions analysis in real samples and shows huge application prospects in point-of-care testing. Herein, a portable, wearable and smartphone-controlled microfluidic electrochemical sensor based on surface tension gradients driving fluid flow was firstly proposed for analysing Cu2+. [Display omitted] . •A wearable POCT system for sweat collection and driving was developed to detect Cu2+.•The surface tension gradient effect achieved non-external driving of electrolytes.•Online flow enrichment of Cu2+ enhanced electrochemical signals during detection.•Laser direct writing ablated micro-channels and LIG for building microfluidic device.•The 3D FC-ZnONRs/LIG increased the electrochemical active sites and conductivity.