Combining optogenetics with flow cytometry Kathrin Brenker123, Luis Köbele123 1Opto Biolabs, Freiburg; 2Centre for Biological Signaling Studies, BIOSS, University of Freiburg; 3Albert-Ludwigs-Universität Freiburg, Germany Keywords Optogenetics, flow cytometry, calcium, cage compound, photoactivation, signaling, cell sorting Abstract Optogenetic tools allow the remote control of cellular pathways using light. This enables the isolated, functional investigation of almost any signaling molecule within complex signaling pathways. More interestingly, the remote control of cellular pathways has major implications for therapeutic tools, including targeted immunotherapy. A major obstacle for optogenetic researchers is the controlled delivery of light to the cell sample and hence the most popular tools for optogenetic studies are microscopy-based cell analyses and in vitro experiments. The flow cytometer has major advantages over a microscope, including the ability to rapidly measure thousands of cells at single cell resolution. However, it is not yet widely used in optogenetics. Opto Biolabs, a spinoff from the University of Freiburg, develops specialized illumination devices enabling the combination of optogenetics and flow cytometry. Optogenetic flow cytometry can be applied for many optically controlled substances including cage compounds or photoconvertible fluorescent proteins and substantially expands the set of possible experiments. Here, we present first results from our research collaborations using this novel technology. Our future work will focus on the expansion of our technology to optogenetic cell sorting, which will greatly simplify the discovery and development of novel, cell-based optogenetic therapies.