Fully-printed microneedles meet plants: a pathway towards easy-to-use NFC monitoring of total ionic conductivity in precision agriculture

This study showcases and validates a fully-printed, low-cost microneedles (MNs) device integrated with environmental sensors and NFC wireless readout for real-time monitoring of changes in plant total ionic conductivity. The Aerosol-Jet printed MNs patch enabled minimally invasive impedance measurements for the monitoring of leaf hydration and ion uptake. Inkjet-printed temperature and humidity sensors provided complementary environmental and leaf's microclimate data. Both sensing platforms were integrated in a cost-effective, easy-to-use wooden clip assembly, granting adhesion and reproducible MNs insertion. Dehydration and ions uptake tests demonstrated that the devices can detect ionic variations in different cellular compartments of the leaves, with distinct responses across plant species reflecting their physiological and anatomical differences. The NFC system validation confirmed that wireless, battery-free readout can be used to observe similar impedance trends with respect to the ones observed with conventional potentiostat measurements. Overall, the presented platform establishes a scalable approach toward simple, field-deployable plant monitoring systems, supporting future development of species-tailored and functionally enhanced sensors for precision agriculture.