Glass integrated optofluidic sensor exploiting dielectrophoresis for label-free detection of bacterial viability

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.