An All-Solid-State Nitrate Ion-Selective Electrode with Nanohybrids Composite Films for In-Situ Soil Nutrient Monitoring

In this paper, an all-solid-state nitrate doped polypyrrole (PPy(NO(3)(−)) ion-selective electrode (ISE) was prepared with a nanohybrid composite film of gold nanoparticles (AuNPs) and electrochemically reduced graphene oxide (ERGO). Preliminary tests on the ISE based in-situ soil nitrate–nitrogen (NO(3)(−)-N) monitoring was conducted in a laboratory 3-stage column. Comparisons were made between the NO(3)(−)-N content of in-situ soil percolate solution and laboratory-prepared extract solution. Possible influential factors of sample depth, NO(3)(−)-N content, soil texture, and moisture were varied. Field-emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD) characterized morphology and content information of the composite film of ERGO/AuNPs. Due to the performance excellence for conductivity, stability, and hydrophobicity, the ISE with ERGO/AuNPs illustrates an acceptable detection range from 10(−1) to 10(−5) M. The response time was determined to be about 10 s. The lifetime was 65 days, which revealed great potential for the implementation of the ERGO/AuNPs mediated ISE for in-situ NO(3)(−)-N monitoring. In-situ NO(3)(−)-N testing results conducted by the all-solid-state ISE followed a similar trend with the standard UV-VIS method.