Fabrication of Electrochemical Nanosensor for Detection of Nitrate Content in Soil Extract

A study was conducted to fabricate and evaluate disposable nanosensor to detect nitrate content in soil extract. Samples collected from three different soil types, under three different nitrogen status (high, medium and low), were tested for the detection of nitrate content. For this purpose, three different electrochemical nanosensors were fabricated using (i) nanocomposite of carbon nanotubes (CNT) and hematite nanostructures (CNT-α-Fe₂O₃/SPE) (ii) along with immobilization of nitrate reductase (NiR) enzyme (NiR/CNT-α-Fe₂O₃/SPE) and (iii) further treated with bovine serum albumin (BSA) (BSA/NiR/CNT-α-Fe₂O₃/SPE). Electrochemical studies of the fabricated nanosensor were conducted using the cyclic voltammetry (CV) technique. The spectroscopic and microscopic characterization studies were performed for revealing the synergic interactions between CNT and α-Fe₂O₃ nanoflowers. Nitrate content in soil for the field experiment varied from 7.6 to 49.47 mg/L. The comparative and validation studies of the fabricated nanosensor were performed with colorimetric method. Among the three different nanosensors tested in this study, the performance of the BSA/NiR/CNT-α-Fe₂O₃/SPE nanosensor was the best, in terms of the electrochemical performance parameters. It was found that the fabricated nanosensor exhibit high sensitivity of 63.87 µA/log(mg/L)/cm² and low detection limit of 0.09 mg/L for the estimation of nitrate content in soil extract. The nanosensor showed good specificity, reproducibility (RSD = 0.43%), high accuracy, and better shelf life (5 weeks). Nitrate detection by the nanosensor was found to be independent of the soil type. The high correlation (r² = 0.998) with the colorimetric method implies futuristic scope of practical utility of the fabricated nanosensor for fast, accurate, and in-field detection of nitrate content in soils during crop cultivation.