Hydrogel Microneedle-Enabled In Situ Monitoring of Leaf Nitric Oxide for Evaluating NO Nanoprodrug-Mediated Salt Stress Alleviation in Maize

Chemical signals in living plants are spatially confined, rapidly consumed, and strongly dependent on the delivery history of exogenous regulators, creating a need for bioelectronic interfaces that can interrogate molecular dynamics directly within intact tissues. Here, we integrate a nitric oxide (NO) nanoprodrug with a conductive hydrogel microneedle platform to connect controlled molecular delivery, in planta electrochemical readout, and downstream biological responses in living maize. The working electrode comprises a poly(vinyl alcohol)/aramid nanofiber (PVA/ANF) hydrogel containing FeMo-N/C and an MXene conductive network. The hydrated microneedle architecture provides tissue-conformal contact and analyte transport, FeMo-N/C enhances the NO-associated electrochemical response, and MXene improves interfacial charge transfer. The resulting platform responds to NO from 1 nM to 100 μM with a detection limit of 0.3 nM and discriminates NO from representative electroactive plant interferents. Chitosan nanoparticles containing S-nitroso-mercaptosuccinic acid were used to moderate NO release, and the microneedle interface resolved treatment-dependent leaf signals over 7 days under salt stress. Signal attenuation by the NO scavenger cPTIO supported the NO-related origin of the electrochemical response. The time-resolved readout was accompanied by improved growth, reduced lipid peroxidation, changes in osmotic and antioxidant responses, and altered expression of stress-responsive genes. This delivery–bioelectronics–analysis framework provides a materials-based strategy for evaluating reactive nanoprodrugs and interrogating transient chemical signaling in living plants.