Optofluidic jet waveguide sensor for Raman spectroscopy

An optofluidic sensor based on a liquid jet waveguide has been successfully applied in Raman spectroscopy. The jet waveguide is obtained by ejecting the solution under analysis through a capillary nozzle. A self-aligned configuration allows to couple the liquid waveguide with an optical probe consisting of two optical fiber respectively used to excite and to detect the Raman signal. As the numerical aperture of a water jet exceeds the one of any other liquid waveguide, a liquid jet ensures high collection and excitation efficiency. Unlike common approaches, this method removes the signal background coming from the substrate avoiding any necessity to contain the solution by means of solid walls. Proof-of-concept measurements performed by means of ethanol-water solution at different concentrations, show limit of detection already competitive with respect different approaches.