Portable Nanohybrid Paper-Based Chemiresistive Sensor for Free Chlorine Detection

[Image: see text] Detecting the concentration of free chlorine is important for monitoring the quality of water. In this study, we report a nanohybrid paper-based chemiresistive sensor that can be used with smartphones to detect free chlorine ions. The sensor was fabricated using a simple and standardized coating process. The graphene and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) nanohybrid paper-based sensing device exhibited a more stable and intuitive response to free chlorine than that exhibited by the device using only PEDOT:PSS. The nanohybrid paper-based sensor was sensitive to free chlorine concentrations in a linear range of 0.1–500 ppm, and the limit of detection was 0.18 ppm. The sensor showed specificity for free chloride ions and detection capability in samples. The sensor was integrated as a module with an electric readout system, and the measured signals and results could be displayed in real time on a smartphone. Therefore, the proposed sensing platform is suitable owing to its portability, low cost, ease of use, and capability for on-site water quality measurement.