Original Tools for Single-Molecule Spectroscopy

Characterizing individually nanoparticles or probing complex environments by single molecule can be a powerful approach provided that spectroscopic techniques, tailored to such systems, have been developed to extract pertinent physico-chemical parameters of interest. In the paper, we report on two techniques that were missing in Single-Molecule Spectroscopy (SMS) toolbox. The first concerns polarization. Due to molecule anisotropy, 3D-molecular orientation is a well-defined parameter. In principle, SMS can take advantage of this property to study 3D-orientation dynamics of the molecule or its environment anisotropy. Unfortunately, information from such measurements is largely reduced because molecules are not efficiently detected when their optical dipole is orientated close to the optical axis. We analyze theoretically this problem and demonstrate experimentally one of its solutions. The second tool is more fundamental. It is chemical analysis of single nanoobjects at room temperature, which is not possible when analyzing fluorescence. With the example of Single-Wall carbon NanoTubes (SWNTs), we show that enhanced Raman spectroscopy allows us to image tiny rope or single SWNTs. We also present preliminary results on enhanced Raman chemical imaging and chemical co-localization.