PROJECT SUMMARY Super-resolution imaging has been a revolutionary technique for biomedical sciences and provided invaluable information about cellular architecture and function at the molecular level with nanometer precision. However, the multiplexing capability and spatial resolution are mainly constrained by the performance of existing fluorescent labels. We propose to develop a palette of bright and switchable fluorescent dyes, referred to as SwitFluor, for multiplexing super-resolution imaging method to simultaneously resolve 6 molecular targets at 10-nm spatial resolution within 10 minutes. We aim to concurrently (1) achieve ultrahigh photon emission rate during the bright state of single-molecule switching process using a newly designed enhancer strand in DNA point accumulation for imaging in nanoscale topography (DNA-PAINT) dye system, and (2) simultaneously switch fluorescence of 6 specially designed spectrally-distinct SwitFluor dyes using orthogonal imager strands for simultaneous imaging with our recently developed spectroscopic single-molecule localization microscopy (sSMLM) optical system. The integration of bright SwitFluor (DNA-PAINT) dyes with sSMLM will collectively achieve the proposed goal. The proposed technology could make a profound impact on a wide range of biological research as we will be able to study complex cellular processes deep down to the molecular scale.