The cobalt (Co) modified polydiacetylenes (Co-PDA) supramolecules have been developed for highly selective colorimetric detection of cyanide anion (CN), a simulant of blood agent. Upon an exposure of CN, our sensory system exhibited blue-to-red color transition due to the twisting of conjugation backbone. The aligned conjugation backbone was twisted by the large distortion force via CN-Co complex formation. Furthermore, we developed luminescent detection system of cyanide ion through the introduction of UCN (upconverting nanocrystal) to Co-PDA.