Cascade signal amplification for ultra-sensitive impedimetric detection of DNA hybridization using a hairpin DNA as probe

An ultra-sensitive impedimetric DNA sensor based on cascade signal amplification in sandwich manner was developed. A hairpin DNA was immobilized on a gold electrode and was acted as a probe DNA to improve the selectivity of the device. Without the target DNA, the hairpin DNA probe was in a closed state. However, in the presence of a target DNA, the hybridization between the loop moiety and the target broke the stem duplex. Consequently, the stem moiety at the 3'-end of the probes was moved away from the electrode surface and available for hybridization with the reporter DNA-Au nanoparticles conjugates (reporter DNA-AuNPs). The thiolated reporter DNA was complementary to the stem moiety at the 3'-end of the probe. After the probe DNA/target DNA/reporter DNA-AuNPs sandwich complex was formed on the electrode surface, the AuNPs were enlarged by immersing the electrode in a growth solution containing a negatively charged surfactant. Cascaded signal amplification was achieved because the electrode surface became more negatively charged after each assembly step. The electron-transfer resistance (Ret) of the DNA sensor increased with the increase in target DNA concentration through a wide linear range from 0.1 fM to 300 fM. Under optimized conditions, the DNA sensor could detect as low as 30 aM of the fully matched target DNA. The sensor also showed excellent differentiation ability for single-base mismatch. (C) 2012 Elsevier Ltd. All rights reserved.