Portable laser-induced graphene sensor for trace picric acid detection in water

A portable electrochemical sensor based on laser-induced graphene (LIG) electrodes modified with graphene/PEDOT:PSS [Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate] hybrid ink is developed for the trace-level detection of picric acid in water. The structural and compositional characterization of the LIG is performed using scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), confirming the successful formation of a conductive graphene network. The working electrode is further modified with graphene/PEDOT:PSS hybrid ink to enhance electrochemical performance. At neutral pH, the sensor exhibited two linear detection ranges of 25 nM to 500 nM and 1 µM to 25 µM, with corresponding limits of detection of 50 nM and 3.8 µM, respectively. Selectivity studies are conducted using common waterborne interfering species, including lead ions, ammonia, hydrazine, nitrate, and hydrogen peroxide, and the results demonstrated high selectivity toward picric acid within the potential window of -1.5 V to +0.2 V. The sensor showed good reproducibility across different devices (n = 7) with deviations below 5%, and acceptable repeatability with deviations in the range of 6-10%. Real sample analysis is performed using lake water spiked with picric acid, yielding recovery values exceeding 95%. Additionally, numerical optimization and experimental EIS validation of the interdigitated electrode geometry are provided.