Imaging of surface O2 dynamics in corals with magnetic micro optode particles

We present a new method for quantifying spatio-temporal O2 distribution and dynamics at biologically active surfaces with a complex surface topography. Magnetized O2 optode microparticles (~80–100 μm) containing the NIR-emitting luminophore platinum (II) meso-tetra(4-fluorophenyl) tetrabenzoporphyrin (PtTPTBPF; ex. max. 615 nm; em. max. 780 nm) were distributed across the surface tissue of the scleractinian coral Caulastrea furcata and were held in place with a strong magnet. The O2-dependent luminescence of the particles was mapped with a lifetime imaging system enabling measurements of the lateral surface heterogeneity of the O2 microenvironment across coral polyps exposed to flow. Mapping steady-state O2 concentrations under constant light and O2 dynamics during experimental light–dark shifts enabled us to identify zones of different photosynthetic activities within a single coral polyp linked to the distribution of coral host pigments. Measurements under increasing irradiance showed typical saturation curves of O2 concentration and estimates of gross photosynthesis that could be spatially resolved at ~100 μm pixel resolution. The new method for O2 imaging with magnetized optode particles has much potential to be used in studies of the surface microenvironment of other aquatic systems such as sediments, biofilms, plant, and animal tissue