Development of ultraviolet-excitation photothermal microscope and observation of a single nonstained biological cell

A system of ultraviolet-laser excitation microscopic photothermal lens imaging for observing chemical compounds in biological cells has been developed, in which a reflection objective lens is used for focusing an excitation laser beam at 260 nm and a probe laser beam at 780 nm. The system enables direct comparison of photothermal and transmitted-light-intensity images to an image of the same object obtained with a complementary metal-oxide-semiconductor image sensor (CMOS). A photothermal lens image of a single yeast cell was successfully obtained and the position of the photothermal images well corresponded to that of the CMOS images.