Abstract: OBJECTIVE To synthesize PDA/PC biosensor capable of specific recognition of cancer cells by immunoassay. METHODS polydiacetylene/phospholipids (PDA/PC) nanoparticle vesicles were prepared by sonication and subsequent EDC/NHS coupling. Anti-Cytokeratin19 monoclonal antibody was covalent linked to PDA/PC nanoparticle vesicle to fabricate a polydiacetylene (PDA)-based colorimetric biosensor for detecting tumor cells. Physicochemical property were characterized by transmission electron microscope negatively staining technique, laser scattering particle size analyzer and UV-Vis spectrophotometer. Colorimetric response CR changing with the amount of CK19 antigen were determined to assess their color change sensitivity. Breast tumour cell line MCF-7 was chosen as a model to evaluate the biosensor to determine the tumor cell with CK19 expressed. RESULTS The PDA/PC biosensors were round or oval with uniform partilcle size of (223.4±23.6) nm measured by TEM. Size by intensity of 298.4 nm and polydispersity index(PDI) of 0.184 were also determined by Malvern Zetasizer 3000HS. The PC/PDA biosensor was agglomerated with the addition of the human CK19 and CR increased with the rising of the concentration of monoclonal antibody solution. Also, the color of the solution was turned from blue to red. CONCLUSION The PDA/PC biosensor has been successfully fabricated for detection of cancer cell based on the chromatic immunoassay with the naked eye-discernible color change. This method is simple, rapid and sensitive and can be a potential technique for CTC recognition by PDA/PC biosensor.