<title>Subsingle-molecule determination of nonfluorescent species by scanning thermal lens microscope and its application to single-cell measurement</title>

ABSTRACT We have developed a thermal lens microscope which induces and detects photothermal effect at sub-single moleculeslevel in/on liquids and condensed media. The thermal lens microscope can determine non-fluorescent molecules withoutreceiving serious effect of light scattering in/on various condensed phase substances, and it can be applied to imaging of thedistribution of non-fluorescent molecules by scanning on the sample. These characteristics of the thermal lens microscopeare suitable for ultra sensitive analysis and imaging of biomedical substance in/on a single cell, separation media, andmicrofabncated chemical devises. We applied the thermal lens microscope to determine an ultratrace chemical species invarious media.Keywords: thermal lens microscope, non-fluorescent molecule, photothermal effect, ultratrace chemical species 1. INTROI)UCTION The relaxation processes of excited molecules can be divided into two processes, radiationless processes, heat, andradiation processes, fluorescence and phosphorescence. In general, the total quantum yield of radiation and radiationlessprocesses is unity for the dipole transition moment. The quantum yield of fluorescence is normally low, and most of themolecules do not fluoresce. Thus, the spectroscopic methods based on the fluorescence lack wide applicability and a more