DEVELOPMENT OF A NOVEL DETECTION METHOD FOR SINGLE NONFLUORECSECT MOLECULES IN LIQUID SOLUTIONS

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One of the ultimate goals of analytical chemistry is to detect certain target molecules in liquid solutions and to observe molecular behavior in-situ. Although techniques based on single molecule detection of biological species begin to provide a variety of new and essential information on the way life works recently, the target molecules are limited to exceptionally highly fluorescent species even for molecule detection in a simple solution. The greater parts of biologically and environmentally important chemicals, such as amino acids, nucleotides, proteins, hormones and so on, are natively nonfluorescent. Thus, we aim to develop ultrasensitive detection methods for nonfluorescent molecules in liquid solutions by improving performance of photothermal spectroscopic techniques. Photothermal spectroscopy is one of the most sensitive detection methods of nonfluorescent chemical species in a liquid solution, and we have reported that photothermal signal is enhanced by two-color exaction, b … More ased on transient absorption and nonradiative relaxation of photoabsorbing molecules. We have experimentally examined absorption spectra of biologically important chemicals, amino acids and nucleotides, and theoretically estimated transient absorption spectra of these chemicals. It is concluded that simultaneous excitation by ultraviolet light and visible or near infrared light could cause photothermal signal enhancement. We proposed that a crossed beam configuration as a suitable optical setup for the ultraviolet-visible simultaneous excitation, and experimentally confirmed that photothermal signal enhancement by the two-color excitation is observed in the crossed beam excitation configuration. We have designed and constructed the ultraviolet-visible two-color excitation photothermal detector and experimentally demonstrated the photothermal signal enhancement for amino acids and some medicines in liquid solutions. In a combination with a micro-HPLC and the detector, we have demonstrated a sensitive separation analysis of nonfluorescent biological specimens. These results are and are being published in scientific literatures. Less