Goro NISHIMURA^* and Masataka KINJO

Research Institute for Electronic Science, Hokkaido University, N12W6, Sapporo 060-0812, Japan

(Received March 5, 2003; Accepted October 9, 2003)

A multi-photon excitation fluorescence correlation system has been developed. The emission from tryptophan methylester solution was observed by this system and analyzed by the intensity correlation function of the visible emission, which originates from the two-photon excitation of photo products generated through a five-photon process. The intensity and the product concentration were proportional to the concentration of tryptophan methylester at a lower concentration range and thus the generation process is a single molecular reaction. The correlation analysis determined the concentration of tryptophan methylester down to 5 μM. The photo product generation from tryptophan solution was enhanced by a potassium iodide addition. These results suggest a new quantification method of tryptophan derivatives.

Key words: fluorescence correlation spectroscopy, multi-photon excitation, single molecule detection, tryptophan, photo kinetics

^*E-mail address: gnishi@imd.es.hokudai.ac.jp