Microfluidic Soil Nutrient Detection System: Integrating Nitrite, pH, and Electrical Conductivity Detection

Soil harbours innumerable microorganisms, nutrients, and other crucial elements, it anchors vegetation and supplies it with the primary factors that make agriculture possible. Soil health is determined by quantifying nutrients and physical parameters that are required to be in optimum range depending on the cropping pattern. In line with this, the current work presents an integrated, low-cost, microfluidic-based system for the detection of three such parameters namely- nitrite, pH and electrical conductivity (EC). A filtration protocol using different grades of Whatman filter paper was established to detect the said parameters using a suspension of soil. A multiplexed polydimethylsiloxane (PDMS) device was designed and fabricated to test for EC and nitrite. The device employed a conductivity cell with copper electrodes, connected in series with a resistor, powered using an oscillating power source. Griess reaction-based photometric detection using an LED and photodiode was used to quantify nitrite. A transimpedance amplifier circuit was designed and fabricated to amplify the photodiode output. pH detection was achieved using a commercially available pH probe and an Arduino pH breakout board. A low-cost 3D printed syringe pump was developed to achieve flow control. Atmega 328P (onboard Arduino Uno) was used to integrate the subsystems. A smartphone application was built to control the system and store geotagged data. Bluetooth protocol was used to communicate between the smartphone application and Arduino. Standards and real soil samples were tested using the developed microfluidic system.