ULTRASENSITIVE NEAR-INFRARED LASER-INDUCED FLUORESCENCE DETECTION IN CAPILLARY ELECTROPHORESIS USING A DIODE-LASER AND AVALANCHE PHOTODIODE

A sensitive fluorescence detector for capillary electrophoresis consis ting of a semiconductor near-infrared diode laser and a single photon avalanche diode (SPAD) is described. The sensitivity of this system wa s demonstrated by the separation and analysis of four tricarbocyanine dyes using capillary electrophoresis and a running buffer consisting o f 98% methanol and 2% water with 40 mM berate (pH 9.4). The LOD for th e dye, IR-132, was found to be 4.41 zmol with the dynamic range found to be approximately four orders of magnitude in concentration. Eased o n the sampling Volume of the system, the number of molecules actually detected at this LOD was approximately 27. To further demonstrate the utility of this diode-based detector, various amino acids were derivat ized with a highly anionic near-IR labelling dye. The conjugates were separated in a running buffer comprised of predominately methanol and a cationic surfactant added to reverse the electroosmotic flow, The LO D values for various amino acids were found to be in the low zmol rang e. (C) 1997 Elsevier Science B.V.