An electrochemical sensor based on screen-printed electrodes for in-situ nitrate measurement in soil-extracted matrices

In recent years, increasing emphasis on sustainable agriculture has highlighted the need for rapid and reliable soil nutrient monitoring, particularly for nitrate, a key determinant of plant productivity and environmental health. However, conventional nitrate analysis methods rely primarily on laboratory-based techniques that are costly, time-intensive, and unsuitable for field deployment. These limitations restrict farmers’ ability to make timely fertilization decisions and contribute to inefficient nitrogen use and environmental contamination. In this study, a portable screen-printed electrochemical nitrate sensor was developed to enable real-time, field-deployable soil analysis. The sensing platform consists of a three-electrode configuration fabricated via screen-printing technology, integrating working, counter, and reference electrodes into a compact format. The working electrode was modified with a nitrate-selective membrane incorporating nitrate-responsive active sites and high-surface-area conductive nanomaterials to facilitate nitrate recognition and impedance-based signal generation. To address membrane instability and signal drift in ion-selective electrochemical systems, a conductive polymeric binding matrix was electropolymerized in situ, forming a robust structural network that enhances long-term signal reproducibility. To examine the electrochemical behavior of the sensor interface and improve analytical reliability, electrochemical impedance spectroscopy (EIS) was employed. The system was modeled using an equivalent electrical circuit to distinguish membrane resistance, double-layer capacitance, and diffusion-related processes associated with nitrate transport at the membrane–electrolyte interface. This impedance-based framework enabled extraction of nitrate-dependent parameters and provided insight into interfacial dynamics governing sensor performance. The developed sensor demonstrated reliable nitrate detection across a concentration range of 1–200 ppm, establishing a strong linear correlation (R² = 0.94) between nitrate concentration and electrochemical response. Incorporation of the electropolymerized binding matrix enhanced stability, reducing relative standard deviation from 17% to 5% over one month. Selectivity tests in the presence of common interfering ions confirmed acceptable specificity under environmentally relevant conditions. Validation was performed using soil filtrates prepared via standardized water extraction protocols for repeatable benchmarking. The impedance-informed analytical framework demonstrated in this work establish a scalable electrochemical sensing platform for precision agriculture. The developed system provides a pathway toward direct soil insertion sensors capable of continuous real-time nitrate monitoring, supporting data-driven fertilization strategies and more sustainable nutrient management practices.