Laser-Induced Graphene-Based Resistive Leaf Wetness Sensors for Pesticide Spray Deposition

Monitoring pesticide spray deposition across crop canopies requires low-cost sensors capable of quantifying deposition through leaf wetness, yet carbon-based resistive leaf wetness sensors (LWS) have not been benchmarked against commercial systems. Here, we demonstrate a scalable resistive laser-induced graphene (LIG) LWS patterned as an interdigitated electrode for pesticide spray monitoring. The sensor achieved normalized wetness values of 0.15, 1.79, and 2.66% cm^-2 after 1, 2, and 5 s of spraying, compared with 0.18, 1.26, and 1.91% cm^-2 for a commercial Onset LWS, indicating greater sensitivity at longer exposures. Calibration followed a formulation-dependent power-law relationship between resistance and deposited volume. Across three independently fabricated sensors, the selected double-lased 0.7 mm IDE produced a reproducible tap-water calibration, with A = 45.167 ± 1.841, n = -0.957 ± 0.021, and R ² = 0.9921. Short-term stability depended on solution and environment, with tap-water calibration changing only 1.5% under greenhouse conditions and 6.3% outdoors after three days, while pesticide formulations exhibited greater drift. Repeated pesticide exposure also caused formulation-dependent drift, indicating that formulation-specific calibration and deployment protocols are required. Overall, the low-cost, scalable LIG LWS offers a promising platform for distributed pesticide spray monitoring and precision agriculture.