A microneedle sensor for in-vivo sodium ion detection in plants.

This study introduces a novel microneedle-type potentiometric sensor designed for the in-vivo detection of sodium ions (Na) in plant tissues. The development of this sensor is crucial for advancing our understanding of plant responses to salinity stress. The microneedle sensor employs a highly selective Na ion carrier and integrates a solid-contact layer made of poly(3,4-ethylenedioxythiophene)-poly (sodium 4-styrenesulfonate) (PEDOT: PSS) prepared by electropolymerization. Due to its excellent conductivity and high chemical stability, PEDOT:PSS significantly reduces the surface impedance of the electrode, enhances charge transfer efficiency, and thereby improves the sensor's response sensitivity and stability. The sensor achieves a linear detection range of 1 × 10 to 1 × 10 M, with a slope of 56.55 ± 0.25 mV/decade and a detection limit of 1.94 × 10 M. The fabrication process was optimized by refining the membrane formulation, ensuring precise control over membrane thickness, and determining the optimal conditioning time, all essential for large-scale production and agricultural applications. In addition, we evaluated the sensor's ability to detect Na concentration changes in both artificial culture media and actual plant tissue samples. The sensor's performance was assessed through its capability to monitor Na concentration changes in both artificial culture media and real plant tissue samples, with results benchmarked against the standard method (ICP-OES), confirming its accuracy and reliability. Moreover, application trials involving rice seedlings validated the microneedle sensor's efficacy for in vivo detection of Na, providing a robust tool for understanding plant physiological responses to salt stress. These findings not only offer new insights into plant adaptation mechanisms but also establish a practical platform for selecting salt-tolerant cultivars and enabling rapid salt-level assessment in agricultural practices.