Light-emitting-diode-induced fluorescence detection of fluorescent dyes for capillary electrophoresis microchip with cross-polarization method

A cross-polarization scheme is presented to filter out the excitation light from the emission spectrum of fluorescent dyes using green light emitting diodes as a light source and a linear charge coupled device as an intensity detector. The excitation light was linearly polarized and was then used to illuminate the fluorescent dyes in the microchannels of a capillary electrophoresis microchip. The detector was shielded by the second polarizer, oriented perpendicular to the excitation light. The fluorescent signals from Rhodamine B dyes were measured in a dilution series with resulting emission signals and four different concentrations of fluorescent dyes were detected simultaneously with the same excitation source and detector. A limit-of-detection of 1 μM was demonstrated for Rhodamine B dye under the optimal conditions.