Micro-fabricated electrochemical chloride ion sensors: From the present to the future

The real-time detection and monitoring of chloride ion concentrations play important roles in broad industrial applications, including wearable health care device, environmental pollutant control and infrastructure corrosion monitoring. The development of all-solid-state micro-fabricated electrochemical sensors has enabled the miniaturisation of these testing devices. This study reviewed the micro-fabricated electrochemical chloride sensors developed since 1970s, together with a brief summary regarding the progression of miniaturised electrochemical sensors in the past half century. Three major types of electrochemical chloride sensors with specific ion-selectivity have been discussed, the potentiometric sensors (including both ion-selective electrodes and chemical FETs), the chronopotentiometric sensors and the voltammetric sensors. In addition, colorimetric sensors, an emerging low-cost, portable, fast diagnose sensor technique has been included in this review. Four critical sensor performances have been reviewed and compared systematically, the sensibility (chloride concentration range), selectivity, lifetime and applicable pH ranges. The future perspectives for engineering applications proposed in this review will benefit the further development of integrated multi-functional sensors, as well as new instrumental testing methods.