An optical device that has an antireflection function includes: a base; and a plurality of structural bodies, which are formed by convex portions or concave portions, arranged on a surface of the base with a fine pitch that is equal to or smaller than a wavelength of visible light. Particularly, the hydrogel of the present invention is made up of copolymers that can be a hydrogel when in an oxidized state and can be a solution when in a reduced state. The carriage is slidable on the path of travel on the cylinder between the first and second ends. The invention further relates to a device for the rapid detection of Bcl-2 in a bodily fluid and methods for rapidly measuring Bcl-2 in a bodily fluid.