Ultratrace Analysis Using Semiconductor Laser as an Exciting Source

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A semiconductor laser is small, intense, less expensive, and can be easily operated. Then, we developed an analytical method using this semiconductor laser for trace analysis.1. High-performance liquid chromatography (HPLC) based on semiconductor laser fluorimetry: We developed a micro-flow cell, consisting of a fused silica capillary and an optical fiber. The detection limit obtained was 12 fg (fg = <10^(-15)> g) for a near-infrared fluorescent dye. After sample separation by HPLC, we detected near-infrared dyes by semiconductor laser fluorimetry. The detection limit was 0.3 pg. We labeled protein in human serum with indocyanine green and separated by HPLC. By this method we could detect 1.3 pmol of albumin. In order to measure biological molecules, we developed a new analytical method based on near-infrared fluorimetry and enzyme reaction. We found that the fluorescence intensity of indocyanine green decreases with increasing the concentration of <H_2> <O_2> . Then, we could measure the activity of xanthine oxidase in the presence of xanthine. We could construct an analytical curve between 0-1 unit.2. Thermal lens spectrophotometry using optical fibers: In the near-infrared region absorption bands due to overtone vibrations are observed. We developed thermal lens spectrophotometry using a couple of optical fibers. The method using a multimode optical fiber has a good coupling efficiency but the output beam profile was very poor giving poor focal properties. Then, it was unsuitable for sensitive detection. On the other hand the method using a single mode optical fiber has a good spatial profile, and it was about 50 times more sensitive than conventional absorption spectrometry.