Graphene oxide based soil moisture microsensor for in situ agriculture applications

In this paper, we have designed a robust graphene oxide (GO) based capacitive sensor which is highly sensitive to soil moisture. The sensor consists of inter-digitated electrode (IDE) with chemically synthesized GO as the sensing platform. We have used the MEMS fabrication technique to fabricate the IDE. We have performed the characterization such as AFM, RAMAN and XPS on the as-prepared GO to understand the surface properties of the GO. The sensor response changes by 340% and 370% over soil moisture changes from 1% to 55% for red and black soil, respectively. GO sensor array shows a fast response time of 100-120 seconds for the soil moisture measurements. For in situ soil moisture measurements, the diurnal temperature and salt concentration (soil conductivity) are the variable parameters, which might affect the sensor response. We observed that the sensor output changes by 6% when the ambient temperature varies from 25 degrees C to 65 degrees C, which leads to just 3% discrepancies for the soil moisture measurements. For the salt concentration (soil conductivity) measurements we noted that the sensor output changes by 4% when salt concentration in the soil sample varies from 0 mol to 0.35 mol (standard for the field measurement), and discrepancies in the soil moisture measurements is around 2%.