Smartphone-assisted portable electrochemical sensing platform for point-of-care detection of thiocyanate using a...

Thiocyanate (SCN^-) poses dual health threats as both a toxic food additive in dairy products and a biomarker for tobacco smoke exposure in smokers' saliva. Existing detection platforms fail to simultaneously address the conflicting demands for high-sensitivity food analysis (0.1-10 ppm) and rapid point-of-care testing in biological fluids (50-200 μM). In this work, a dual-purpose portable electrochemical SCN^- sensor was developed based on a laser-induced graphene (LIG) composite electrode. The flexible and miniaturized graphene sensing platform was fabricated via UV laser patterning on polyimide substrates. Poly(3,4-ethylene dioxythiophene) (PEDOT) was functionally modified onto the electrode surface via in-situ electropolymerization, forming a conductive polymer-graphene hybrid composite electrode. Owing to the synergistic effects of LIG's outstanding physical properties and PEDOT's high conductivity, the composite electrode exhibited remarkable electrochemical performance for thiocyanate detection. Under optimized conditions, the sensor demonstrated a wide linear response range (10-300 μM), a high sensitivity of 3.06 μA μM^-1cm^-2, and a low detection limit of 0.52 μM (S/N = 3) through differential pulse voltammetry. Selective detection was achieved in complex matrices containing common interferents. Long-term stability tests revealed 94.2 % signal retention after two weeks of storage. Integrated with microfluidic sampling and a smartphone-based potentiostat, the handheld portable device enabled rapid SCN^- analysis within just 1 min. Practical validation using milk and artificial saliva samples showed recovery rates of 96.2-105.5 %, highlighting its potential for food safety inspection and health monitoring. This work provides a cost-effective (<$0.5) approach for field-deployable food safety systems and personalized health management.