Imaging single 5 nm gold nanoparticles through interferometric cross-polarization microscopy

The authors present a novel method that detects individual nanoparticles by their modification of the polarization state of the light detected in a confocal arrangement. This method allows the full retrieval of the amplitude and phase response of individual gold nanoparticles down to 5 nm in diameter at wavelengths far from the plasmon resonance as shown in the paper. The authors realized this detection scheme at the very low excitation intensities (~1μW) needed for single molecule fluorescence and bioimaging experiments. The attraction of this new approach lies in the fact that it in principle can be used for the shot-noise limited detection of a whole range of different particle types, ranging from single molecules to nanometer sized gold particles. Results on different types of nanoparticles as well as preliminary results on imaging MDCK cells will be presented.