Quick and simple integration of optical oxygen sensors into glass-based microfluidic devices

Abstract

This work presents a novel simple and inexpensive technique for integration of optical oxygen sensors into microfluidic chips made of glass. The channels of chips are coated with conjugated polymeric nanoparticles containing a covalently grafted oxygen indicator. The resulting layer of physically adsorbed nanoparticles shows excellent stability in buffers of various pH and in presence of a surfactant without noticeable leaching. The integrated sensors feature ultrafast response (less than 0.2 seconds) and repeatable quenching behavior when exposed to different concentrations of oxygen present in air or aqueous solutions. They can be read-out either in lifetime or in ratiometric intensity modalities using unsophisticated, compact and low-cost fluorescence detection systems such as a dual RGB/NIR camera or a phase fluorometer. We also present a new technique for modification of smooth glass surfaces based on in situ generation and deposition of dense silica microparticles, which act as an adsorbent for the oxygen-sensitive nanoparticles. This modification dramatically improves the loading with the nanoparticles due to increased surface roughness and maximized contact surface area. Finally, packed-bed micro reactors with integrated oxygen-sensing layers and filled with silica beads containing the enzyme immobilized on its surface are demonstrated to have high potential for investigation of enzymatic activity.