Multi-Sample Detection of Soil Nitrate Nitrogen Using a Digital Microfluidic Platform

The rapid quantification of nitrate nitrogen concentration plays a pivotal role in monitoring soil nutrient content. Nevertheless, the low detection efficiency limits the application of traditional methods in rapid testing. For this investigation, we utilized a digital microfluidic platform and 3D-printed microfluidics to accomplish automated detection of soil nitrate nitrogen with high sensitivity across numerous samples. The system combines digital microfluidics (DMF), 3D-printed microfluidics, a peristaltic pump, and a spectrometer. The soil solution, obtained after extraction, was dispensed onto the digital microfluidic platform using a micropipette. The digital microfluidic platform regulated the movement of droplets until they reached the injection area, where they were then aspirated into the 3D-printed microfluidic device for absorbance detection. Implementing this approach allows for the convenient sequential testing of multi-samples, thereby enhancing the efficiency of nitrate nitrogen detection. The results demonstrate that the device exhibits rapid detection (200 s for three samples), low reagent consumption (40 µL per sample), and low detection limit (95 µg/L). In addition, the relative error between the detected concentration and the concentration measured by ultraviolet spectrophotometry is kept within 20%, and the relative standard deviation (RSD) of the measured soil samples is between 0.9% and 4.7%. In the foreseeable future, this device will play a significant role in improving the efficiency of soil nutrient detection and guiding fertilization practices.