The invention relates to an adapter-based optical chemical biosensor and a method thereof for detecting a target molecule, in particular to an optical chemical biosensor used for identifying a target molecule for example, a polydiacetylene structure organized molecular assembly of nucleotide, amino acid, polypeptide, protein, entire cell, other specific molecules and the like, by using an adapter, and a method for detecting the target molecule by using the optical chemical biosensor for the polydiacetylene structure organized molecular assembly. In the optical chemical biosensor, an adapter for a specific binding target molecule is combined on the surface of the polydiacetylene structure organized molecular assembly so that the specific target molecule can be detected / identified through the changed ultraviolet-visible light absorbency or fluorescence intensity of the polydiacetylene structure organized molecular assembly when the specific target molecule is exposed outside the corresponding adapter.