Opto-Microfluidics for Monitoring Salinity and Temperature of Sea Water
The success of ocean observation relies on effective monitoring technologies with increased functionalities, minimized size, and reduced cost, which can only be achieved through the development of new technologies. Opto-microfluidics has been increasingly recognized as powerful technologies to realize miniaturized devices for environmental monitoring, biological analyses, and chemical syntheses. By combining microfluidics and optics technologies, roomful laboratory equipment can be integrated into a palm-size chip with merits of versatile functionalities, compactness, minimized waste, and low cost. These opto-microfluidic systems are promising for applications in ocean observation.In this study, opto-microfluidic devices for monitoring salinity and temperature of liquids are proposed and demonstrated with ultrafast laser fabrication and two-photon polymerization techniques. By applying femtosecond lasers as powerful tools to achieve laser microfabrication with unprecedented high precision and quality, a Mach-Zehnder interferometer (MZI) has been fabricated and integrated into a microchannel as a miniaturized opto-microfluidic system. When saline solution or sea water is introduced to the microchannel, different phase shifts in the MZI can be resulted, which allow determination of the salinity and temperature of the solution from output optical spectra and intensities of the MZI corresponding to different phase shifts. The sensitivities of salinity and temperature have been found to be 215.744 nm/RIU and 0.519 nm/oC for the opto-microfluidic systems developed in this study, respectively. The results demonstrate the practicability of opto-microfluidic devices for real-time salinity and temperature monitoring of sea water in harsh environment.