Imaging of surface [O.sub.2] dynamics in corals with magnetic micro optode particles

We present a new method for quantifying spatio-temporal [O.sub.2] distribution and dynamics at biologically active surfaces with a complex surface topography. Magnetized [O.sub.2] 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 [O.sub.2]-dependent luminescence of the particles was mapped with a lifetime imaging system enabling measurements of the lateral surface heterogeneity of the [O.sub.2] microenvironment across coral polyps exposed to flow. Mapping steady-state [O.sub.2] concentrations under constant light and [O.sub.2] 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 [O.sub.2] concentration and estimates of gross photosynthesis that could be spatially resolved at ~100 µm pixel resolution. The new method for [O.sub.2] 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.