In this work, we present two micro-opto-fluidic platforms for smart recognition of water-based fluids exploiting absorption spectroscopy. The identification of the samples is based on their absorption properties in the near infrared region from 1165 nm to 1650 nm and, in particular, on the analysis of the absorption band of water located around 1450 nm. In the instrumental setup, the fiber-coupled light emitted by a Tungsten lamp is shone onto the micro-devices and the output radiation is directed to an optical spectrum analyzer. The first platform works in reflection by means of a rectangular glass micro-capillary with integrated reflectors. Thanks to the presence of the double metallization, light can cross the capillary channel multiple times in order to enhance measurement sensitivity. The second platform works in transmission and exploits a commercial device with a micro-fluidic polymeric channel. The performances of the sensing platforms were initially theoretically studied by implementing a MATLAB® model based on geometrical optics and Lambert-Beer formula for absorption. Then, experiments were carried out by testing water-alcohol dilutions, proving results in a good level of agreement with the theoretical predictions. We also successfully employed our platforms for specific measurement of the water content in Scottish whisky and Venezuelan white rum liquor. The proposed readout technique is remote, contactless, non-invasive, and thus totally safe. Moreover, borosilicate glass micro-capillary and polymeric channel are both sterile, biocompatible and low-cost devices. These features make our opto-fluidic-platforms highly suitable also for many other applications, ranging from biology to food analysis.
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