Liquid Concentration Sensing Module Based on Multi-Quantum Well Light Emitting Diodes

Light source and photodetector are necessary elements for liquid concentration sensing system. Normally, two different devices are needed to realize these functions. The coexistence of emission and detection properties in multi-quantum well light emitting diodes (MQWs LEDs) brings convenience to the design of new concentration sensors. In this letter, we present a transmission-type sensing module using two identical AlGaInP red LEDs. With a designed collimation system, any two LEDs can form a sensing channel. Concentration-induced optical signal changes will be transformed into various photocurrents on the receiving side and realize a sensing. Choosing methylene blue solution as the tracer agent, the sensing performance of the system is evaluated. The sensor can detect methylene blue solution concentrations in the range of 0 to 24.23~\mu mol/L, providing a novel measurement approach for monitoring substances in wastewater.