Solid-state diode laser-induced fluorescence detection in high-performance liquid chromatography

The need to measure ultralow levels of pharmaceuticals in biological matrices at femtogram and attogram levels presents a significant challenge to bioanalysts. Liquid chromatography has proven to be a versatile and valuable tool for separating analytes from complex biological matrices and fluorescence detection provides both the sensitivity and the selectivity required to measure femtogram and attogram levels of analytes. Solid-state diode lasers have been used primarily in printers, compact disc recorders, and bar code scanners but have recently been adapted for use as light sources for fluorescence detection. Excellent spectral features in the visible and near-infrared regions of the spectrum, together with low cost and ruggedness, make diode lasers an attractive alternative for use as light sources in analytical measurement. Biological matrices demonstrate minimal background signals in the far-red regions of the spectrum which diode lasers emit and diode lasers are among the most stable light sources available. These facts along with expected developments in labeling systems make the potential for use of diode lasers in LC-detection quite promising. This paper reviews characteristics of diode lasers, the properties of potential visible and near-infrared fluorescent probes, instrumental aspects of diode laser fluorometers, and future trends that can be expected in this exciting field of bioanalytical research.