Abstract: A micro-discharge optical source apparatus and a method and system which utilizes the apparatus to analyze a sample are provided. The apparatus includes a substrate and an anode electrode and a cathode electrode supported on the substrate. One of the electrodes, such as the cathode, is preferably a liquid electrode. The electrodes are spaced apart to define an inter-electrode gap therebetween. The apparatus further includes a voltage source for applying a voltage between the electrodes sufficient to generate a glow micro-discharge in the gap to cause a first emission having a first desired excitation spectrum. An optical element is integrated with the substrate to direct the first emission to travel along an optical path including an axis. In one embodiment, the system detects the direct fluorescence of a sample such as tryptophan and other amino acids. In another embodiment, the system detects fluorescence of dye-labeled biochemicals.