This paper reports an optofluidic water-jet waveguide used for laser-induced fluorescence spectroscopy. In this common analytical technique, the sensitivity depends on the ratio between the fluorescent signal and the background signal. The signal intensity is essentially related to the collection efficiency of the detection optics, whereas the background signal (noise) has two main contributions: the excitation source scattering and the fluorescence arising from non-analyte substances that the light source encounters along its path. In order to increase the signal-to-background ratio, recently, a great effort has been addressed towards the development of novel optical excitation/detection configuration [1-4]. In this paper an innovative configuration is proposed, where a high-speed water stream produced by means of a microchannel acts at the same time as the solution to analyse and the collecting optical waveguide. Water-jet waveguides are sometimes used in laser cutting device [5], and very few examples in fluorescence spectroscopy applications have been proposed, however, without fully exploiting the great advantage of this device [6, 7]. Furthermore, the few configurations proposed in literature require bulky optic and fluidic device with careful alignment procedure. Our configuration allows to minimize the pump contribution in the detected signal and to avoid any problem related to non-analyte fluorescence arising, for instance, from the walls of the flow cell typically used in this spectroscopic technique. In addition the configuration proposed is auto-aligned and integrated as the water-jet waveguide is directly coupled with the receiving optical fibre which collects the fluorescence light to a low-cost minispectrophotometer.
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