Integrated photonics on glass offers advantages for sensing applications because of its relative low cost and its detection sensitivity. In this paper we discuss the design, fabrication and characterization of a micro device for sorting and sensing dielectric microparticles. The target application is the analysis of bacteria used as sentinel for water pollution. The sorting function, that does not include any functionalization layer, is done by means of dielectrophoretic forces. They are induced by castellated electrodes fed by a low frequency electric signal. The sensing function is obtained by a surface waveguide that is perturbed by the particles collected on top of it by dielectrophoresis. We first discuss the co-integration of the castellated electrodes with an optical waveguide. An efficient interaction of polystyrene beads with the guided light (up to 50% of intensity modulation) is then simulated and observed experimentally. We also showed that this multiphysics device can be used as a sensor, presenting curves of the intensity modulation depending on the concentration of beads. The attenuation in the optical signal varies between 2 and 5 dB with particle concentrations ranging from 136 to 455 beads per μL in the analyte.
Water quality monitoring faces technological challenges such as rapid and in-situ measurements, using reusable, compact and easy-to-clean devices. Glass integrated photonics is an attractive solution: it exhibits a high sensitivity to absorption or interferometric measurements, and glass is chemically compatible with aqueous environments. An innovative idea for pollution detection is to assess the bacterial cellular viability as a global indicator for pollutant toxicity. This study proposes an original concept of integrated opto-fluidic sensor which sorts and quantifies the dead or alive bacteria in a liquid sample. To ensure a robust label-free detection, the cells discrimination is provided by a selective trapping of the bacteria exploiting dielectrophoretic effects. This avoids the use of a functionalization layer. The device comprises a photonic circuit made by silver-sodium ion-exchange on glass. The sensing area co-integrates a single-mode waveguide and aluminum electrodes designed to generate dielectrophoretic forces. Both waveguide and electrodes can be encapsulated inside a polydimethylsiloxane microfluidic channel for the flow of the bacterial suspensions. In this study, charged polystyrene beads (Sigma-Aldrich, CLB9) dispersed in deionized water have been used to model dead bacteria. We observed an intensity modulation of the guided light (up to 8% of the output power) at a wavelength of 1550 nm, by selectively controlling the beads trapping. We also correlated the beads collection by microscopy imaging.
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