Bimetallic Porphyrin-Based Metal–Organic Framework for Noninvasive Electrochemical Monitoring of Nitric Oxide in Plants and Fruits

Abstract As environmental and climatic changes intensify, plants and fruits are frequently exposed to abiotic stresses, leading to excessive accumulation of nitric oxide (NO) and disruption of cellular redox homeostasis, so noninvasive monitoring of NO is of great importance. In this study, MX@Fe/NiPor-MOF was constructed at room temperature by assembling a bimetallic porphyrin-based metal–organic framework (Fe/NiPor-MOF) with transition metal carbide nanosheets (MX), and further integrated with screen-printed carbon electrodes (SPCEs) for noninvasive NO detection in plants and fruits. The cooperative interaction between Fe/Ni bimetallic centers enabled efficient electron redistribution, with Ni acting as an electron reservoir to facilitate rapid and reversible Fe2+/Fe3+ redox cycling. Meanwhile, the porous MOF structure and highly conductive MX promoted the exposure of Fe–N4/Ni–N4 active sites and established efficient electron transport pathways. Benefiting from these structural and electronic advantages, the MX@Fe/NiPor-MOF/SPCE electrochemical sensor exhibited excellent electrocatalytic performance toward NO detection, including a wide linear range (0.5–565.5 μM), a low detection limit (0.14 μM), a high sensitivity (1.95 μA·μM–1·cm–2), and excellent anti-interference capability. As a proof of concept, the platform enabled real-time, noninvasive electrochemical monitoring of microscale NO release from plant and fruit tissues subjected to thermal treatment and mechanical wounding. This work highlights the role of bimetallic synergy in enhancing NO electrocatalysis and provides a promising strategy for in situ monitoring of gaseous signaling molecules in plant and fruit tissues.