Self-sacrificial label assisted electroactivity conversion of sensing interface for ultrasensitive electrochemical immunosensor.

Sensitivity amplification strategies in electrochemical immunoassays are mainly limited by redox signal leaking, degradation of catalytic activity caused by layers of decoration and the large hindrance effect caused by immunoprobes. Herein, we developed an innovative sensitivity amplification strategy based on the self-sacrificial label-assisted electroactivity conversion of a sensing interface, utilizing Fe-loaded polydopamine (Fe-PDA) nanoparticles as the self-sacrificial labels, which can be decomposed under acidic conditions and release Fe. When the assembled sensing interface was immersed in a prussian blue (PB) precursor solution (a mixed solution of 0.1 M KCl, 0.1M HCl and 1 mM KFe(CN)), the as-formed sandwich-type structure was destroyed due to the decomposition of Fe-PDA caused by HCl in PB precursor solution, resulting in the reduce of interface resistance. The released Fe reacted with the PB precursor solution and triggered the growth of electroactive PB nanoparticles (PB NPs) on the sensing interface. Assisted by self-sacrificial Fe-PDA, the sensing interface was converted from electrochemically inactive to electroactive with a strong redox signal, high catalytic activity, and decreased interface resistance. The PB NPs can catalyse HO to amplify the redox signal, thus improving sensitivity. The redox signal and catalysts were generated in the final assembly step, which can avoid signal leaking and decreases of catalytic activity caused by layers of decoration. The decomposition of Fe-PDA can eliminate the large hindrance effect of the immunoprobe. Ultrasensitive quantification of carbohydrate antigen 125 (CA 125) was realized with a detection range from 0.00001 to 1000 U mL and detection limit of 0.25 × 10 U mL.