Chip-Scale In Situ Salinity Sensing Based on a MonolithicOptoelectronic Chip

Salinity is an indispensable parameter for variousapplications such as biomedicaldiagnostics, environmentalchemical analysis, marine monitoring, etc. Miniaturized salinitysensors have significant potential in portable applications in variousscenarios and designs with highly desirable features of convenience,reliability, economy, and high sensitivity and also the capability ofreal-time measurements. Herein, we demonstrate a highly refractiveindex-sensitive sensor based on a microscale III-nitride chip thatconsists of a light emitter and a photodetector. This highlymonolithically integrated chip shows an excellent sensitivity ofsalinity of 2606 nA/(mol/L) (or 446 nA/%) and a response timeof 0.243 s. In addition, wireless communication technologies canbe easily integrated with the sensing device, which enables automatic remote control for data collection and postprocessing.Remarkably, a polymer-based antifouling coating on the surface of the sensing chip has been established to significantly improve itslong-term stability in mimicked marine water. The demonstrated ultrasensitive, ultracompact, cost-effective, fast response, wireless-compatible, and easy-to-use features endow the current device with a huge potential for in situ salinity sensing under varyingenvironmental conditions