Functional Imaging of Chemically Active Surfaces with Optical Reporter Microbeads

Abstract

We have developed a novel approach to allow for continuous imaging of concentration fields that evolve at surfaces due to release, uptake, and mass transport of molecules, without significant interference of the concentration fields by the chemical imaging itself. The technique utilizes optical “reporter” microbeads immobilized in a thin layer of transparent and inert hydrogel on top of the surface. The hydrogel has minimal density and therefore diffusion in and across it is like in water. Imaging the immobilized microbeads over time provides quantitative concentration measurements at each location where an optical reporter resides. Using image analysis in post-processing these spatially discrete measurements can be transformed into contiguous maps of the dynamic concentration field across the entire surface. If the microbeads are small enough relative to the dimensions of the region of interest and sparsely applied then chemical imaging will not noticeably affect the evolution of concentration fields. In this work colorimetric optode microbeads a few micrometers in diameter were used to image surface concentration distributions on the millimeter scale.

Electrochemical mapping of oxygenation in the three-dimensional multicellular tumour hemi-spheroid

“…Thus, if we 'remove' the lower half of the MCS (grey half circle in figure 3b) what remains is the equivalent MCH (yellow in figure 3b) but with a 'window' exposed, available for both non-contact imaging and direct sensing modalities that require contact with the interstitial fluid. Combinations are also possible, such as an optical indicator membrane underneath the MCH whose colour distribution is then imaged in a non-contact fashion [67,68]. The remaining problem to solve is how to make hemi-spheroids such that high-throughput culture and analysis become feasible.…”