In Situ Monitoring of Stress-Induced Hydrogen Peroxide in Plants Using NIR-II Fluorescent Microneedles

In situ monitoring of plant responses to stress is one of the most challenging aspects of precision agriculture, and the dynamic control of crop growth according to fluctuating environmental factors. Although fluorescence imaging provides a nondestructive approach for monitoring stress-related biomarkers, its performance is often hindered by the low abundance of endogenous signaling molecules and strong tissue autofluorescence. Here, we report a microneedle-integrated sensing platform that enables sensitive detection of endogenous hydrogen peroxide (H₂O₂) in living plants. The platform incorporates a second near-infrared fluorescent nanoprobe composed of Er³⁺-doped lanthanide nanoparticles emitting at 1550 nm and Mo-doped polymetallic oxomolybdates serving as the H₂O₂-responsive unit. Embedding the nanoprobe into custom-fabricated microneedles allows precise positioning on plant midribs for continuous monitoring of H₂O₂ dynamics. Under stress conditions, the system successfully visualized spatiotemporal fluctuations of H₂O₂ in living tomato, spinach, and tobacco plants. This work establishes a strategy for early stress diagnosis and developing universal plant health monitoring technologies.