Ultrasensitive near-infrared laser-induced fluorescence detection in capillary electrophoresis using a diode laser and avalanche photodiode.

A sensitive fluorescence detector for capillary electrophoresis consisting of a semiconductor near-infrared diode laser and a single photon avalanche diode (SPAD) is described. The sensitivity of this system was demonstrated by the separation and analysis of four tricarbocyanine dyes using capillary electrophoresis and a running buffer consisting of 98% methanol and 2% water with 40 mM borate (pH 9.4). The LOD for the dye, IR-132, was found to be 4.41 zmol with the dynamic range found to be approximately four orders of magnitude in concentration. Based on 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 derivatized 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 LOD values for various amino acids were found to be in the low zmol range.