An Electrochemical Microfluidic System for On-site Continuous Monitoring of Soil Phosphate

On-site monitoring of phosphate concentration has attracted much attention recently for soil fertility management in agricultural products. This study proposes a portable and easy-operate electrochemical microfluidic system with integrated reagent reactions for on-site continuous monitoring of soil phosphate. Polydimethylsiloxane (PDMS) chips with channel layers and PDMS substrates embedded with screen-printed electrodes (SPEs) were prepared using 3-D printed molds. Reagents and samples were pumped into the chips at optimal flow rates of $100~\mu \text{L}$ min $^{-{1}}$ to automatically react, which were used for cyclic voltammetry (CV) electrochemical detection of analytes via carbon black nanoparticles (CBNPs) modified electrodes. After optimizing experimental conditions, including pH value, liquid flow rates, and voltammetry scan rates, the system achieved a linear phosphate concentration range of 5– $100~\mu \text{M}$ with a detection limit (LOD) of $4.2~\mu \text{M}$ ; moreover, the system exhibited excellent resistance to interference long lifespan and excellent phosphate recovery rate from 91.1% to 110.48%. This system has been successfully applied to continuous field phosphate determination in real soil environments. Results elucidated that the system has good practicality and great potential for fine nutrient management in the field.