Non-contact and specific detection of nitrate and phosphate mixtures by microfluidic microwave sensor array

Industrial wastewater includes a large amount of nitrogen and phosphorus ions, which can cause environmental pollution. This study proposed a microfluidic radiofrequency sensing system to achieve non-contact detection of nitrogen and phosphorus ions in their mixed solutions. The system consists of internal split-ring resonator array and microfluidic module. Due to the array's multiple resonant points, it can offer more detection information, making it suitable for the analysis of complex samples. Through joint simulation of microfluidic radiofrequency sensing system, the optimal microfluidic sizes are determined. The results indicate that the detection sensitivity of the system for sixteen types of mixed solutions (represented by resonant frequency f, insertion loss S21, and phase phi) ranges from 0.0002 to 0.029 (1/(mu g/mL)). The range of microwave synthesis parameter compositeprincipal component analysis (CPCA) projection values for sixteen types of mixed solutions is from -2.98 to 2.1, enabling the decoupling of mixed solution types and concentrations. The neural network is also proposed to predict the concentrations of the mixed solutions.