Polydiacetylene (PDA), a conjugated polymer, has attracted attention for realization of a label-free real-time colorimetric biosensor because it exhibits large and rapid colorimetric responses upon the binding of biomolecules. This is due to the conformational distortion of its conjugated backbone. However, solid-state PDA biosensors for point-of-care diagnosis remain unexplored. We describe a highly sensitive solid-state biosensor based on PDA liposomes. We employed gold nanoparticles (AuNPs) on PDA liposomes as the molecular-binding-signal sensitizer, which provides additional conformational distortion in the backbone structure of PDA by exerting steric repulsion to the attached biomolecules. To prove the concept, AuNPs and a thrombin-binding-aptamer were individually functionalized on PDA liposomes, which were attached to a substrate for the detection of thrombin. We found that the sensitivity was enhanced 2.5 times in the presence of AuNPs compared with the case without AuNPs. Because the steric repulsion of the AuNPs is target-independent, we believe that our solid-state biosensor provides a path toward advanced solid-state biosensors.