Hollow PDA-Au nanoparticles-enabled signal amplification for sensitive nonenzymatic colorimetric immunodetection of carbohydrate antigen 125

A novel colorimetric immunoassay was designed for the sensitive detection of carbohydrate antigen 125 (CA125). The success of this immunoassay relies on the use of hollow polydopamine-gold nanoparticles (PDA-Au) for signal amplification to achieve sensitive nonenzymatic colorimetric detection. In particular, PDA-Au was used as a stable and sensitive label and aminated-Fe3O4 magnetic nanoparticles (Fe3O4 NPs) were employed to immobilize capture antibody (Ab1) and acted as a separable immunosensing probe. PDA-Au exhibited high catalytic performance towards p-nitrophenol reduction and thus resulted in significant color change and UV/vis signal variations. The immunoassay was performed based on sandwich protocol. As compared to pure Au nanoparticles, the signal amplification and sensitivity of PDA-Au-based assay was significantly improved. For instance, the dynamic range of the developed colorimetric immunoassay for CA125 was 0.1-100 U/mL with a detection limit of 0.1 U/mL at S/N=3. In addition, this immunoassay was also tested for the analysis of clinical serum samples, which demonstrated its potential for practical diagnostic applications.