Electrochemical sensor using coffee peel-derived MnO-doped porous carbon detects salicylic acid in avocado leaves infested with red spider mites

Salicylic acid (SA) plays a crucial role in inducing resistance in various plant species against pests, viruses, fungi, and bacterial pathogens. The dynamic changes in SA concentration can serve as real-time indicators of plant immune system activation, offering valuable biological markers for the early detection of diseases and pest infestations. This study develops an electrochemical sensor using MnO-anchored porous carbon (PC-MnO) derived from waste coffee peels for sensitive SA detection. The enhanced sensing mechanism relies on three key aspects: (1) The hierarchical porous carbon framework derived from coffee peels, in conjunction with the chemical activator and pore-forming agent Zn 2+ , facilitates efficient electron transfer and provides a high specific surface area; (2) Uniform MnO nanoparticles provide electrocatalytic sites that lower the oxidation overpotential of SA; (3) Strong interfacial coupling between carbon and MnO facilitates charge transfer kinetics. The optimized sensor shows a detection limit of 16.67 nmol/L and successfully quantifies SA in avocado leaves, revealing significantly elevated levels (96.82 μmol/L) in mite-infested leaves versus healthy controls (0.79 μmol/L). This work presents a sustainable sensing platform that supports early plant stress detection and advances smart agriculture.