DNAzyme-functionalized gold–palladium hybrid nanostructures for triple signal amplification of impedimetric immunosensor

A highly sensitive and selective impedimetric immunosensor with triple signal amplification was designed for ultrasensitive detection of prostate-specific antigen (PSA) by using anti-PSA antibody and DNAzyme-functionalized gold–palladium hybrid nanotags (Ab 2 –AuPd–DNA). The signal was amplified based on the Ab 2 –AuPd–DNA toward the catalytic precipitation of 4-choloro-1-naphthol (4-CN). DNAzyme (as a kind of peroxidase mimic) could catalyze the oxidation of 4-CN, whilst AuPd hybrid nanostructures could not only provide a large surface coverage for immobilization of biomolecules but also promote 4-CN oxidation to some extent. The produced insoluble benzo-4-chlorohexadienone via 4-CN was coated on the electrode surface , and hindered the electron transfer between the solution and the electrode, thereby increasing the Faradaic impedance of the base electrode . Three labeling strategies including Ab 2 –AuNP, Ab 2 –AuPd and Ab 2 –AuPd–DNA were investigated for determination of PSA, and improved analytical features were obtained with the Ab 2 –AuPd–DNA strategy. Under optimal conditions, the dynamic concentration range of the impedimetric immunosensor spanned from 1.0   pg   mL −1 to 50   ng   mL −1 PSA with a detection limit of 0.73   pg   mL −1 . Intra- and inter-assay coefficients of variation were below 8.5% and 9.5%, respectively. Importantly, no significant differences at the 0.05 significance level were encountered in the analysis of 6 clinical serum specimens and 6 diluted standards between the impedimetric immunosensor and the commercialized electrochemiluminescent method for PSA detection.