“Off−On” Electrochemical Hairpin-DNA-Based Genosensor for Cancer Diagnostics
journal contributionposted on 01.03.2011, 00:00 by Elaheh Farjami, Lilia Clima, Kurt Gothelf, Elena E. Ferapontova
A simple and robust “off−on” signaling genosensor platform with improved selectivity for single-nucleotide polymorphism (SNP) detection based on the electronic DNA hairpin molecular beacons has been developed. The DNA beacons were immobilized onto gold electrodes in their folded states through the alkanethiol linker at the 3′-end, while the 5′-end was labeled with a methylene blue (MB) redox probe. A typical “on−off” change of the electrochemical signal was observed upon hybridization of the 27−33 nucleotide (nt) long hairpin DNA to the target DNA, in agreement with all the hitherto published data. Truncation of the DNA hairpin beacons down to 20 nts provided improved genosensor selectivity for SNP and allowed switching of the electrochemical genosensor response from the on−off to the off−on mode. Switching was consistent with the variation in the mechanism of the electron transfer reaction between the electrode and the MB redox label, for the folded beacon being characteristic of the electrochemistry of adsorbed species, while for the “open” duplex structure being formally controlled by the diffusion of the redox label within the adsorbate layer. The relative current intensities of both processes were governed by the length of the formed DNA duplex, potential scan rate, and apparent diffusion coefficient of the redox species. The off−on genosensor design used for detection of a cancer biomarker TP53 gene sequence favored discrimination between the healthy and SNP-containing DNA sequences, which was particularly pronounced at short hybridization times.
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electrochemical signalelectrochemical genosensor responsecancer biomarker TP 53 gene sequenceDNA beaconsSNPgenosensor selectivityadsorbate layertarget DNACancer DiagnosticsAalkanethiol linkerMB redox labelscan ratehairpin DNADNA hairpin beaconsgenosensor platformredox labelredox speciesDNA hairpin20 ntshybridization timeselectron transfer reactionredox probeDNA duplexdiffusion coefficientgold electrodes