Communication. A simple laser-induced fluorescence detector for sulforhodamine 101 in a capillary electrophoresis system: detection limits of 10 yoctomoles or six molecules
High sensitivity fluorescence detection was generated for capillary electrophoresis based on a post-column sheath-flow cuvette. An inexpensive 8 mW He–Ne laser operating at 594 nm was used for excitation of Sulforhodamine 101. This dye, which is commonly used for both protein labelling and deoxyribonucleic acid (DNA) analysis, has molar absorptivity that is matched to the laser wavelength. Collection efficiency was doubled compared with previous work by using two microscope objectives, one located on each side of the illuminated sample stream. A series of injections of Sulforhodamine 101 was performed; the average detection limit (3σ) was 6 ± 1 molecule of dye injected onto the capillary. These injections ranged from 250 to 17 molecules of dye. Both the detection limits and the amount of injection are the lowest ever reported in capillary electrophoresis. The mass sensitivity of this detector is at least two orders of magnitude lower than the best on-column capillary electrophoresis fluorescent detector.