Free chlorine ultra-sensitive detection in tap water via an enrichment-sensing process by an interdigitated microelectrode sensor

•An interdigitated microelectrode sensor chip was designed and batch fabricated.•TSAM is proposed to improve the sensitivity of sensor though an enrichment-sensing process.•About 30 times increase in sensitivity of sensor by TSAM is witnessed, comparing with others. Electrochemical free chlorine sensor is considered to be a feasible device for on-line monitoring of free chlorine in tap water due to their reagent-free and short-response-time etc. However, the low sensitivity and the difficulty of to mass-production of the sensor always are the stubborn issues for reliable detection and application in ultra-low concentration range. In this paper, we design an interdigitated microelectrode structured electrochemical sensor chip for free chlorine sensing in tap water and fabricate by MEMS. The batch-fabricated sensor demonstrates an acceptable limit of detection (