Semiconductor Laser-Induced Fluorescence Spectroscopy in Pico-liter Volume Flow-Cells

In this study the potential of using visible semiconductor lasers as the excitation source for laser-induced fluorescence spectroscopy (LIF) of nano-liter to pico-liter samples has been evaluated. The incentive to work with LIF in the upper visible and near infrared wavelength region is the possibility to design a system that is not limited by any background fluorescence, e.g. from a capillary flow-cell or the liquid eluent [1]. The system described here was mainly designed for applications to chemical ultra-trace analysis when combined with miniaturized separation techniques such as capillary liquid chromatography and capillary electrophoresis. A concentration limit of detection in the lower pico-molar range (6.3 - 58 · 10-12 mol/L) was obtained for a model fluorescent compound, HITCI (1,1’,3,3,3',3'-hexamethyl-indotricarbocyanine iodide). The smallest illuminated volume was 0.7·10-12 L using an 11 μm inner diameter fused silica capillary flow-cell. These figures compares well with the best obtained using conventional gas-lasers for LIF [2,3]. An important advantage with the semiconductor LIF system, except from that it is inexpensive, is that the compactness and the high performance of the components makes it highly suitable for portability.