Continuous Monitoring of Soil Nitrate Using a Miniature Sensor with Poly(3-octyl-thiophene) and Molybdenum Disulfide Nanocomposite

There is an unmet need for improved fertilizer management in agriculture. Continuous monitoring of soil nitrate would address this need. This paper reports an all-solid-state miniature potentiometric soil sensor that works in direct contact with soils to monitor nitrate-nitrogen (NO3--N) in soil solution with parts-per-million (ppm) resolution. A working electrode is formed from a novel nanocomposite of poly(3-octyl-thiophene) and molybdenum disulfide (POT-MoS2) coated on a patterned Au electrode and covered with a nitrate-selective membrane using a robotic dispenser. The POT-MoS2 layer acts as an ion-to-electron transducing layer with high hydrophobicity and redox properties. The modification of the POT chain with MoS2 increases both conductivity and anion exchange, while minimizing the formation of a thin water layer at the interface between the Au electrode and the ion-selective membrane, which is notorious for solid-state potentiometric ion sensors. Therefore, the use of POT-MoS2 results in an improved sensitivity and selectivity of the working electrode. The reference electrode comprises a screen-printed silver/silver chloride (Ag/AgCl) electrode covered by a protonated Nafion layer to prevent chloride (Cl-) leaching in long-term measurements. This sensor was calibrated using both standard and extracted soil solutions, exhibiting a dynamic range that includes all concentrations relevant for agricultural applications (1-1500 ppm NO3--N). With the POT-MoS2 nanocomposite, the sensor offers a sensitivity of 64 mV/decade for nitrate detection, compared to 48 mV/decade for POT and 38 mV/decade for MoS2. The sensor was embedded into soil slurries where it accurately monitored nitrate for a duration of 27 days.

农业中对改进肥料管理存在未满足的需求。对土壤硝酸盐的持续监测将满足这一需求。本文报道了一种全固态微型电位土壤传感器，它与土壤直接接触，以百万分之一（ppm）的分辨率监测土壤溶液中的硝态氮（NO3 - -N）。工作电极由一种新型的聚（3 - 辛基噻吩）和二硫化钼（POT - MoS2）纳米复合材料制成，该材料涂覆在有图案的金电极上，并使用机器人分配器覆盖一层硝酸盐选择性膜。POT - MoS2层作为具有高疏水性和氧化还原特性的离子 - 电子转换层。用MoS2对POT链进行修饰可提高导电性和阴离子交换能力，同时最大限度地减少在金电极和离子选择性膜之间界面处形成薄水层，这对于固态电位离子传感器来说是个棘手的问题。因此，使用POT - MoS2可提高工作电极的灵敏度和选择性。参比电极包括一个丝网印刷的银/氯化银（Ag/AgCl）电极，其覆盖有质子化的Nafion层，以防止在长期测量中氯离子（Cl - ）的浸出。该传感器使用标准和提取的土壤溶液进行校准，其动态范围涵盖了所有与农业应用相关的浓度（1 - 1500 ppm NO3 - -N）。使用POT - MoS2纳米复合材料时，该传感器对硝酸盐检测的灵敏度为64 mV/十倍浓度，相比之下，POT为48 mV/十倍浓度，MoS2为38 mV/十倍浓度。该传感器被嵌入土壤泥浆中，在27天内准确监测硝酸盐。