A fiberoptic sensor made by coating the tip of a (glass) optic fiber with an antibody that fluoresces when the antibody comes in contact with its corresponding antigen. Alternatively, the fiber tip is sometimes coated with a dye that fluoresces when the dye comes in contact with specific chemicals (e.g., oxygen, glucose, etc.). Functionally, a beam of light is sent down the fiber and strikes (“pumps”) the fluorescent complex, which then fluoresces (releases light of a specific wavelength). The light produced by fluorescence travels back up the same optic fiber and is detected by a spectrophotometer upon its return. By application of the Beer-Lambert Law, quantitative detection/measurement of the antigen or chemical in vivo in, for example, a patient’s bloodstream is possible.