Cooperative amplification-based electrochemical sensor for the zeptomole detection of nucleic acids

In this work, we developed a multiple-amplification-based electrochemical sensor for ultrasensitive detection of nucleic acids using a disease-related sequence of the p53 gene as the model target. A capture probe (CP) with a hairpin structure is immobilized on the electrode surface via thiol-gold bonding, while its stem is designed to contain a restriction site for EcoRI. In the absence of target DNA, the probe keeps a closed conformation and forms a cleavable region. After treatment with EcoRI, the target binding portion (loop) plus the biotin tag can be peeled off, suppressing the background current. In contrast, the CP is opened by the target hybridization, deforming the restriction site and forcing the biotin tag away from the electrode. On the basis of the biotin-streptavidin complexation, gold nanoparticles (GNPs) modified with a large number of ferrocene-signaling probes (Fc-SPs) are captured by the resulting interface, producing an amplified electrochemical signal due to the GNP-based enrichment of redox-active moieties. Furthermore, Fc tags can be dragged in close proximity to the electrode surface via hybridization between the signaling probes and the CP residues after EcoRI treatment, facilitating interfacial electron transfer and further enhancing the signal. With combination of these factors, the present system is demonstrated to achieve an ultrahigh sensitivity of zeptomole level and a wide dynamic response range of over 7 orders of magnitude.