Modular Impedimetric Sensing Platform for Laboratory and Field Characterization in Precision Agriculture

Precision horticulture demands affordable and versatile platforms to test a variety of sensors. However, current solutions are often costly, complex, and limited in scope, hindering widespread adoption. Here, we present a modular and practical sensor system designed for the integration and evaluation of printed impedimetric sensors. The platform includes an impedance analyzer, two 16-channel multiplexers, and a Raspberry Pi. Using the developed data acquisition system, we fully characterized the electrical impedance spectroscopy response of an ammonia gas sensor and three humidity sensors over a frequency range from 500 Hz to 10 MHz. The chemiresistive ammonia sensor, tested in a controlled laboratory environment using a gas exposure setup, showed optimal operation at 4 kHz, demonstrating high sensitivity in impedance magnitude measurements. In contrast, the paper-based humidity sensors were evaluated directly on plants under field conditions, where analysis of phase angle (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Theta$</tex-math></inline-formula>) and impedance magnitude (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula>) identified optimal measurement points. At lower frequencies (below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{4}$</tex-math></inline-formula> Hz), both parameters showed strong correlations with relative humidity, with correlation coefficients of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.52 \pm 0.03$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-0.54 \pm 0.02$</tex-math></inline-formula>, respectively. These results indicate a capacitive response to moisture absorption and good reproducibility between devices. Beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{5}$</tex-math></inline-formula> Hz, the correlation weakened, indicating a transition in sensor response mechanisms. Our results demonstrate the effectiveness of the platform in both laboratory and field environments, providing a robust and cost-effective tool to evaluate impedimetric sensors. By enabling rapid and accurate assessments, this system advances agricultural technology for more efficient, sustainable precision horticulture.