Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.10.29.360214v1?rss=1 Authors: Gielen, V., Mönkemöller, V., Shen, Y., Hofkens, J., Vanden Berghe, P., Campbell, R. E., Moeyaert, B., Dedecker, P. Abstract: Genetically-encoded biosensors based on a single fluorescent protein are widely used to visualize analyte levels or enzymatic activities in cells, though usually to monitor relative changes rather than absolute values. We report photochromism-enabled analyte quantification (PEAQ) biosensing, a method that leverages photochromic properties of biosensors to provide an absolute measure of the analyte concentration or activity. We develop photochromic variants of the popular GCaMP family of calcium ion biosensors, and show that these can be used to resolve dynamic changes in the absolute Ca2+ concentration in live cells. We also show how our method can be expanded to fast imaging with reduced illumination intensities or to situations where the absolute illumination intensities are unknown. In principle, PEAQ biosensing can be applied to other biosensors with photochromic properties, thereby expanding the possibilities for fully quantitative measurements in complex and dynamic systems. Copy rights belong to original authors. Visit the link for more info