Dark Field Microspectroscopy with Single Molecule Fluorescence Sensitivity

Dark field microscopy directly detects scattering from a sample by rejecting excitation light. The technique has been extensively used for spectral characterization of nanoscopic particles, but its sensitivity has been limited by residual stray light. Here, we present a simple geometry based on wide field illumination under normal incidence capable of background suppression by more than 7 orders of magnitude. The setup is optimized for spectrally resolved wide-field detection with white light illumination. We record images and spectra of single 10 nm gold particles binding to a functionalized surface, demonstrating a more than 2 orders of magnitude improvement in sensitivity over the current state of the art. Our level of stray light rejection allows us to record single molecule fluorescence images with broadband excitation without any filters in the detection path. The approach is ideally suited for investigations of truly nanoscopic objects with applications in single molecule and nanoparticle spectroscopy, plasmonic sensing, and ultrafast spectroscopy.