Sorting Sounds - A high-throughput microfluidics screening platform for the development of genetically encoded labels for Optoacoustic imaging

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Optoacoustic (OA) or Photoacoustic imaging is an emerging imaging modality providing unsurpassed penetration depth at high resolutions. This provides for more comprehensive time resolved 3D in vivo imaging at depths far beyond the reach of optical methods. However, with the application of OA in life sciences being relatively new the range of labels and molecular tools is limited. Thus far only a small number of dedicated labels has been put forward with an even smaller number being genetically encoded - a prerequisite for targetable in vivo imaging. From the molecular perspective a wide range of labels known from fluorescence imaging - especially green fluorescent protein (GFP) like labels - could be utilized for OA. However, while fluorescence imaging aims for a high molecular brightness (i.e. quantum yield) the concept of OA requires a predominantly radiation-less deexcitation pathway. This fundamental difference makes an immediate application of the rich variety of fluorescence imaging tools in OA problematic. Furthermore, near-infrared labels are required to access the full advantage of the higher penetration depth intrinsic to OA imaging. Consequently, a new range of molecular labels has to be designed for OA to fully empower this new imaging modality. Next to the design principles a fundamental prerequisite to protein based label engineering is the ability to screen for the desired properties of the label. In the case of the design of genetically encoded fluorescence labels screening could rely on the detection of fluorescence signals. However, new screening strategies have to be applied for OA-label engineering. The research outlined in this proposal includes design of a microfluidics based high-throughput OA cytometry device as well as proof-of-concept directed-evolution and screening for OA-optimized labels. In preliminary work we could already demonstrate the feasibility of faithfully detecting OA signals in single cells in a microfluidics configuration and outlined the technical prerequisites. Furthermore, we tested several red GFP-type chromo-proteins in OA to identify candidates most suitable as starting points for library generation.