A new photoelectrochemical immunosensor for ultrasensitive assay of prion protein based on hemin-induced photocurrent direction switching.

As a significant biomarker of prion diseases, ultrasensitive assay of infectious isoform of prion (PrPSc) is highly desirable for early diagnostics of prion diseases. Herein, taking normal cellular form of prion (PrPC) as a model owing to a high risk of pathogenicity of PrPSc, a new photoelectrochemical immunosensor has been developed based on hemin-induced switching of photocurrent direction. In the presence of PrPC, nitrogen-doped porous carbon-hemin polyhedra labeled with secondary antibody were introduced onto the CdS-chitosan (CS) nanoparticles-modified indium-tin oxide (ITO) electrode via the antigen-antibody specific recognition. Because of the matched energy level between CdS and hemin, the high-efficiency switch of photocurrent direction of the ITO/CdS-CS photoelectrode from anodic to cathodic photocurrent was observed even at very low concentration (0.4 aM) of PrPC. Through changing the specific antibody, this method can be easily expanded to PrPSc assay. Such low detectable limit is very useful in the early diagnosis and screening of prion diseases. The developed method has also promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.