RESEARCH ARTICLE Functional Imaging of Chemically Active Surfaces with Optical Reporter Microbeads

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, with-out 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 dif-fusion in and across it is like in water. Imaging the immobilized microbeads over time pro-vides 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 evolu-tion 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