The inadequate use of fertilizer leads to an imbalance of nitrogen in soil, which presents significant challenges to sustainable agriculture. To address this issue, a novel soil nitrogen sensor using reduced graphene oxide (rGO)-based field-effect transistor (FET) is proposed. In soil, nitrogen is present in the form of nitrate, nitrite, and ammonium ion; however, as nitrite content is exceptionally low, the detection of nitrite is not possible. Most of the research focuses on nitrate detection, but simultaneous detection of nitrate and ammonium ions is highly significant and challenging. The proposed concept enables a single FET device to detect both ammonium and nitrate ions at different gate potentials. The sensor demonstrates a very high response of 1050% for 3.5-ppm nitrate ion with a sensitivity of 0.9 µA/ppm and 860% for 3.5-ppm ammonium ion with a sensitivity of 0.45 µA/ppm at an optimized V_gs of 3.9 and 0.8 V, respectively. Moreover, the sensor exhibits promising attributes, including high selectivity and rapid response (35 s for NO₃^- ions and 41 s for NH₄⁺ ions). This facilitates real-time monitoring of soil nitrogen levels for precision agriculture applications.

A precise measurement of soil potassium (K) concentration is crucial for enhancing agricultural productivity and promoting sustainable land management. The efficiency of real-time soil quality monitoring is hampered by the time-consuming laboratory analysis that is commonly associated with conventional methods. The present research introduces an innovative approach utilizing a field-effect transistor (FET) structure coated with reduced graphene oxide-decorated valinomycin (rGO-v) for the detection of potassium ions in soil samples. The sensor exploits the distinctive electrical properties of reduced graphene oxide (rGO) and the specific affinity of valinomycin for potassium ions. To construct the device, we applied rGO-v onto an FET substrate. The conductance of the FET can be modified by the interaction between valinomycin and potassium ions, enabling the detection of potassium ions. Some of the advantages of this technology are its high sensitivity, fast response time, and potential for miniaturization. In addition, the device is tuned to demonstrate an enhanced sensitivity of 0.98 μA/(kg/ha) below the threshold voltage. The sensor exhibits a response time of 40 s and demonstrates exceptional stability in the face of unfavorable conditions, specifically humidity. Therefore, valinomycin-decorated reduced graphene oxide, when subjected to appropriate gate bias, demonstrates promising results as a versatile, cost-effective, and easy-to-use potassium ion sensor.

Graphene is the most fascinating material due to its exceptional electrical and mechanical properties. The reduced form of graphene oxide (GO) is best suitable for sensor applications. There are numerous methods available for reducing GO by synthetic reducing agents that are not environment-friendly and cost-effective. Therefore, in this research work, natural lemon juice is used as a potential reducing agent. It creates defects on the GO surface by altering various functional groups. These are clearly visible in Raman and FTIR results and help in the sensing of the lead (Pb²⁺) and cadmium (Cd²⁺) ions. Field effect transistor (FET) based active structure is used to amplify its sensitivity and discriminate the lead and cadmium ions by tuning the gate voltage. The optimized gate voltages for lead (Pb²⁺) and cadmium (Cd²⁺) ions are -1.6 V and 0.8 V, respectively, at which the sensor shows the maximum response. This green synthesis approach of sensor fabrication highlights sustainable and cost-effective solutions in the field of reduced graphene-based FET sensors.

According to the World Health Organization (WHO), mercury is one of the top ten toxic groups of substances that can pose the greatest threat to human life. Very minor contamination with mercury can adversely impact the nervous, digestive, and immune systems of the lungs, kidneys, skin, and eyes, resulting in severe health problems, including death. Conventional detection techniques are incredibly complex, costly, and lack portability. This article describes a highly sensitive, selective, and stable field effect transistor (FET)-based sensor for efficiently detecting mercury ions in water. Glutathione-reduced graphene oxide (glu-rGO) is chosen as the sensing material. The operating gate voltage of the device is optimized to -4.98 V to achieve maximum response. At a gate voltage of -4.98 V, the device's sensitivity is evaluated as 1.04μA/ppb for 1.2 ppb mercury compared to 0.51μ A/ppb at zero gate voltage. The device is tested against six common heavy metal ions and is found to be highly selective toward mercury. Therefore, the glu-rGO-based FET device is promising for future portable, economical, and user-friendly mercury ion detector systems.