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In this work, we present a compact micro-opto-fluidic sensing platform for the measurement of volumetric refractive index (RI) variations of ultra-low volumes of fluids with respect to a reference liquid. In the instrumental configuration, we employed a disposable plastic micro-channel, which was customized with integrated back and front aluminum reflectors, deposited by sputtering. The presence of the double metallization is exploited to create a zigzag guiding path for the radiation provided by a semiconductor laser diode, so that light crosses the fluid under test multiple times before reaching a 1-D Position Sensitive Detector (PSD). According to Snell law, when fluids with different RI indices fill the channel, the radiation is deflected at different angles and the output beam shifts along the channel surface. RI variations are monitored by measuring the position of the output light spot on the surface of the PSD. To validate the results, a theoretical model based on ray optics was developed to study the propagation of the radiation travelling through the fluidic channel. Experimental results showed a beam displacement per RI unit up to 3234 μm/RIU, in agreement with the prediction of the analytical model. The proposed sensing method is label-free, contactless, non-invasive, and biologically safe. Moreover, the micro-opto-fluidic sensing platform could be exploited in a wide range of applications, ranging from biology to medicine to the agri-food industry.

A novel flexible supercapacitor device was developed from a polyethylene terephthalate substrate, reused from beverage bottles, and a conductive ink based on carbon black (CB) and cellulose acetate (CA). The weight composition of the conductive ink was evaluated to determine the best mass percentage ratio between CB and CA in terms of capacitive behavior. The evaluation was performed by using different electrochemical techniques: cyclic voltammetry, obtaining the highest capacitance value for the device with the 66.7/33.3 wt% CB/CA in a basic H2SO4 solution, reaching 135.64 F g−1. The device was applied in potentiostatic charge/discharge measurements, achieving values of 2.45 Wh kg−1 for specific energy and around 1000 W kg−1 for specific power. Therefore, corroborated with electrochemical impedance spectroscopy assays, the relatively low-price proposed device presented a suitable performance for application as supercapacitors, being manufactured from reused materials, contributing to the energy storage field enhancement.