APPLICATION OF AN AVALANCHE PHOTODIODE IN A NEAR-GEIGER OPERATION AS A FLUORESCENCE DETECTOR FOR CAPILLARY ELECTROPHORESIS

A laser-induced fluorescence detection system for capillary electropho resis has been developed by use of a semiconductor laser (655 nm) as a n excitation light source and an avalanche photodiode (APD) as a fluor escence detector. The APD may be used in a near-Geiger condition by ad justing its bias voltage, and its internal gain to photoelectrons incr eases substantially. Subnanosecond time-resolved photon counting using the APD in the near-Geiger operation has provided very high sensitivi ty due to its well-defined photoelectron pulse shape and an enhancemen t of the counting efficiency. The detection limit of Oxazine 725 was 4 7 amol, which was about 100 times better than that using a photomultip lier.