Stem-FIT: a Microneedle-based Multi-parametric Sensor for In Situ Monitoring of Salicylic Acid and pH Levels in Live Plants

This work reports Stem-FIT: a first-of-its-kind three-dimensional printed microneedle-based electrochemical sensor for real-time monitoring of plants’ primary defense-related phytohormone, salicylic acid. In addition, a pH sensor was integrated on the same chip to enable pH correction of the measured salicylic acid levels based on the variations in sap pH. The sensor was demonstrated to measure the salicylic acid and pH levels in the stem of unstressed and water-stressed cabbage plants in real-time. The sensor was capable of detecting salicylic acid levels down to 37 μM. Real-time measurements of SA levels in plant sap with built-in pH correction capability can help growers act timely against any environmental stress conditions to mitigate crop productivity losses and improve plants’ adaptability to stressors.