Monitoring soil pH variation using Polyaniline/SU-8 composite film based conductometric microsensor

Development of Poly-aniline/SU-8 (an epoxy resin) nanocomposite film based conductometric microsensor platform to measure change in soil pH is reported. For this, poly-aniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) was mixed with SU-8, and spun coated on Au-IDE patterned on Si/SiO2. The nanocomposite exhibited excellent response towards change in pH against three different conditions, namely standard buffer solutions with pH ranging from 2 to 10, Red and Bentonite soils, wherein the pH varied with water (soil moisture contents) and pH with different concentrations of calcium chloride (CaCl2) solution. The films exhibited the sensitivities of 455 and 290 mu S/pH towards acidic (Lower pH) and alkaline solutions (Higher pH), respectively. The sensitivities of 34 and 89 mu S/pH with water for Red and Bentonite soil samples, respectively were obtained. Importantly, for Red and Bentonite soils, the sensitivities of 41 and 52 mu S/pH with CaCl2 concentration were achieved. Moreover, the sensor revealed faster response kinetics with response and recovery times of (similar to)10 and (similar to)30 s respectively. Overall, the sensor exhibited good sensitivity, excellent long term stability, high repeatability and low fabrication cost. Our results demonstrated that PANI/SU-8 composite films as a potential material for the determination of soil pH variation crucial for precision agriculture.