Miniature multiple wavelength excitation and emission optical system and method for laser-induced fluorescence detectors in capillary electrophoresis

Abstract

An optical apparatus for and method of improving collection efficiency and signal strength of optical instruments used in capillary electrophoresis, such as laser-induced fluorescence detectors are provided. The apparatus and method provides a concave reflector positioned at one side of the capillary flow cell as a first high numerical aperture (N.A.) collector, a lens collector positioned at an opposite side of the flow cell as a second high N.A. collector, and an optical fiber positioned at close proximity of the flow cell for delivery of an excitation light to cause a sample contained in the flow cell to emit emission lights. The reflector has a concave surface for reflecting the emission lights, and the collector has a proximal convex surface for collecting the emission lights, and a distal convex surface for collimating the emission lights. This arrangement achieves a larger solid collection angle from both sides of the flow cell and therefore an increased collection efficiency. Two or more optical fibers may be used to deliver excitation lights from different sources. The optical fibers are arranged in a plane orthogonal to the optical axis of the reflector and collector to reduce the interference from the scattered background lights and therefore improve the signal to noise ratio. The collimated emission lights can be detected by, e.g., a photo-multiplier tube detector.