Water-jet waveguide for fluorescence spectroscopy

An optofluidic sensor based on a liquid-jet waveguide is presented. The waveguide consists of a high-speed water jet produced by means of a microchannel coupled with a multimode optical fibre collecting the fluorescence opportunely excited. The liquid jet acts, at the same time, as the solution to analyse and as an optical waveguide. This configuration allows a strong reduction of the scattering and fluorescence of non-analyte substances enabling a very low limit of detection (LOD). The integrated device is fabricated by PMMA micro-machining allowing a self-alignment between the liquid-jet waveguide and the optical fibre used to deliver the fluorescence to the detector. The performance of the system has been tested on Cy5 water solutions and LOD of 2.56 nM has been obtained. A proof-of-concept of filter-free measurements has been performed demonstrating that fluorescence measurements can be performed also by using a photodiode with an LOD of 6.11 nM. © 2014 Springer International Publishing Switzerland.