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A new homogeneous electrochemical sensing strategy based on exonuclease III-assisted target recycling amplification was utilized for simple, rapid and highly sensitive detection of human immunodeficiency virus (HIV) DNA on an immobilization-free Ag(I)-assisted hairpin DNA through the cytosine–Ag + –cytosine coordination chemistry. The assay involved target-induced strand-displacement reaction accompanying dissociation of the chelated Ag + in the hairpins and exonuclease III-triggered target recycling. Initially, the added target DNA hybridized with hairpin DNA to disrupt the Ag(I)-coordinated hairpin probe and releases the coordinated Ag + ion. Then, the newly formed DNA double-stranded DNA could be cleaved by exonuclease III, and released target HIV DNA, which retriggered the strand-displacement reaction with the hairpin for target recycling, thereby resulting in formation of numerous free Ag + ions in the detection cell. The released Ag + ions can be readily captured by the negatively charged electrode, and subsequent anodic-stripping voltammetric detection of the captured Ag + ions are conducted to form the anodic current for the production of the electronic signal within the applied potential. Under optimal conditions, the exonuclease III-based sensing system exhibited good electrochemical responses for the detection of HIV DNA at a concentration as low as 23 fM. [ABSTRACT FROM AUTHOR]

This article reports on a new square-wave anodic-stripping voltammetric method for sensitive determination of nucleic acids. It is based on a target-induced strand displacement reaction with blocker DNA (labeled with a CdS quantum dot) from a biotinylated hairpin DNA. First, a hairpin-blocker DNA duplex was immobilized on the surface of the well in a microtiter plate via biotin-streptavidin interaction. On addition of target DNA to the well, the CdS-labeled blocker DNA is displaced by target DNA from the hairpin-blocker duplex to form a new target-blocker DNA duplex. This is accompanied by the release of CdS-labeled blocker DNA. Next, cadmium ions are released from the Q-dots (by adding 1 M nitric acid) and then quantified by anodic stripping voltammetry using an in-situ prepared mercury film electrode. The voltammetric signal increases with the concentration of target DNA in the 5.0 pM to 1.0 nM concentration range, and the detection limit is as low as 1.2 pM. The assay has a good repeatability and displays an intermediate precision of down to 10 %. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel silver ion (Ag+)-assisted hairpin DNA through C–Ag+–C coordination chemistry was designed for immobilization-free and label-free electrochemical monitoring of human immunodeficiency virus (HIV) DNA on a negatively charged indium-tin oxide electrode, based on hybridization-induced dissociation of silver ions from the hairpin DNA. [ABSTRACT FROM AUTHOR]