Ultrabright planar optodes for luminescence life-time based microscopic imaging of O 2 dynamics in biofilms

Abstract

New transparent optodes for life-time based microscopic imaging of O 2 were developed by spin-coating a μm-thin layer of a highly luminescent cyclometalated iridium(III) coumarin complex in polystyrene onto glass cover slips. Compared to similar thin-film O 2 optodes based on a ruthenium(II) polypyridyl complex or a platinum(II) porphyrin, the new planar sensors have i) higher brightness allowing for much shorter exposure times and thus higher time resolution, ii) more homogeneous and smaller pixel to pixel variation over the sensor area resulting in less noisy O 2 images, and iii) a lower temperature dependency simplifying calibration procedures. We used the new optodes for microscopic imaging of the spatio-temporal O 2 dynamics at the base of heterotrophic biofilms in combination with confocal imaging of bacterial biomass and biofilm structure. This allowed us to directly link biomass distribution to O 2 distribution under both steady state and non-steady state conditions. We demonstrate that the O 2 dynamics in biofilms is governed by a complex interaction between biomass distribution, mass transfer and flow that cannot be directly inferred from structural information on biomass distribution alone.