Basic Characteristics of Ionic Liquid-Gated Graphene FET Sensors for Nitrogen Cycle Monitoring in Agricultural Soil

Abstract

Nitrogen-based fertilizers are crucial in agriculture for maintaining soil health and increasing crop yields. Soil microorganisms transform nitrogen from fertilizers into ${\mathrm{N}\mathrm{O}}_3^{-}$–N, which is absorbed by crops. However, some nitrogen is converted to nitrous oxide (N₂O), a greenhouse gas with a warming potential about 300-times greater than carbon dioxide (CO₂). Agricultural activities are the main source of N₂O emissions. Monitoring N₂O can enhance soil health and optimize nitrogen fertilizer use, thereby supporting precision agriculture. To achieve this, we developed ionic liquid-gated graphene field-effect transistor (FET) sensors to measure N₂O concentrations in agricultural soil. We first fabricated and tested the electrical characteristics of the sensors. Then, we analyzed their transfer characteristics in our developed N₂O evaluation system using different concentrations of N₂O and air. The sensors demonstrated a negative shift in transfer characteristic curves when exposed to N₂O, with a Dirac point voltage difference of 0.02 V between 1 and 10 ppm N₂O diluted with pure air. These results demonstrate that the ionic liquid-gated graphene FET sensor is a promising device for N₂O detection for agricultural soil applications.