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^-2 to 1 × 10^-5 M, with a slope of 56.55 ± 0.25 mV/decade and a detection limit of 1.94 × 10^-6 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.