Multicolored nanometre-resolution mapping of single protein–ligand binding complexes using far-field photostable optical nanoscopy (PHOTON)

Abstract

Mapping of individual ligand molecules and their binding sites in single protein–ligand complexes at nanometer resolution in real-time would enable probing their structures and functions in vitro and in vivo. In this study, we have developed far-field photostable optical nanoscopy (PHOTON) for mapping single ligand molecules (biotin) and their binding sites in individual protein–ligand complexes (streptavidin–biotin) with 1.2 nm spatial resolution and 100 ms temporal resolution. PHOTON includes one standard far-field optical microscope with a halogen-lamp illuminator; single-molecule-nanoparticle-optical-biosensors (SMNOBS) with exceptionally high quantum-yield (QY) of Rayleigh scattering and photostability (non-photobleaching, non-photoblinking) as imaging probes; and Multispectral Imaging System (MSIS) for spectral isolation of individual SMNOBS with 1 nm wavelength resolution. Intrinsic size- and shape- dependent localized-surface-plasmon-resonance (LSPR) spectra of single SMNOBS provide multiple-spectral (color) nanoprobes for sub-diffraction imaging, offering feasibility of probing of binding structures and functions of single protein–ligand complexes at nm (potentially achieving Ångstrom) resolution in real-time.