HCR-stimulated formation of DNAzyme concatamers on gold nanoparticle for ultrasensitive impedimetric immunoassay

A novel signal-amplified impedimetric immunosensing strategy was successfully developed for ultrasensitive detection of low-abundance proteins (carcinoembryonic antigen, CEA, used as a model) based on hybridization chain reaction (HCR)-stimulated formation of DNAzyme concatamers on nanogold particle accompanying enzyme-triggered biocatalytic precipitation. The assay was carried out on capture antibody-modified electrode by using gold nanoparticle heavily functionalized with initiator strand and detection antibody as the signal-transduction tag with a sandwich-type immunosensing format. In the presence of target CEA, the formed immunocomplex underwent an unbiased strand-displacement reaction by the initiator strand on the gold nanoparticle between two auxiliary single-stranded DNA with the hemin aptamer. Upon hemin introduction, numerous DNAzyme molecules were formed on the concatamers and nanogold particle, which could catalyze 4-chloro-1-naphthol to produce an insoluble precipitation on the electrode, thereby resulting in the amplification of impedimetric signal. Under the optimal conditions, the immuno-HCR assay exhibited good impedimetric responses for the detection of target CEA in the working range from 1.0 pg mL−1 to 20 ng mL−1 with a detection limit of 0.42 pg mL−1. In addition, the immuno-HCR assay was validated by measuring six human serum specimens for target CEA, receiving a highly matched correction between the obtained results by the immuno-HCR assay and the commercialized ELC-based immunoassay method.