Application of nano-sensors in the determination of soil moisture and temperature

Nano-sensors are of extreme precision and reactivity, properties that make them delicate, precise, and sensitive instruments for identifying and responding to physical, chemical, and biological stimuli. Application of nano-sensors in agriculture and, especially in soil science, is a great help toward accurate measurement of soil temperature and moisture. Being equipped with wireless communication systems, they are more economical, easier to use, and user-friendly than other similar instruments. Carbon nanotubes and graphene, wireless sensors, and nanotechnology-based microelectromechanical systems are some of the nano-sensors used in soil investigations. This review study explores the feasibility of using nanotechnology-based, cheap, wireless devices consisting of microcantilever beams for the simultaneous measurement of soil temperature and moisture. The system relies on the principle of shear stress for measuring water vapor, in which a micro-sensor chip is combined with a proprietary nanopolymer sensing element and the Weatstone bridge piezoresistor circuit to deliver two DC output voltages that are linearly proportional to relative humidity in the range of 0% to 100% and to temperature from ‒30 to 100 °C. The graphene quantum dots may be alternatively used to measure soil moisture; these remain stable for about 4 months exhibiting negligible changes in their resistance with time. The response time of the sensor is quite fast (around 2–3 minutes) and the graphene quantum dots are found appropriate for quick and accurate measurement of soil moisture.