Simple and convenient assays with quantum dots (QDs) as the labels for DNA detection are developed. The probe DNA modified with thiol was first immobilized on a pretreated Au electrode, and then the complementary DNA (cDNA) oligonucleotides were hybridized with the immobilized probes by immersing the probe-modified Au electrode into the cDNA oligonucleotide solution. Finally, the avidin-modified QDs were bound to the biosensor in the presence of biotin-modified cDNA. The fabrication process for the biosensor was monitored by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Different from the traditional sandwich-structure strategy, the QDs bind to the target DNA directly via the biotin–avidin-system. By observing the ECL signal and determination of the cadmium component in QDs, the DNA hybridization event was detected by ECL and square wave anodic stripping voltammetric technique (SWASV) respectively. For SWASV detection, the signal linearly increased with the increase of the logarithm of the cDNA concentration over the range of 50 nM ∼ 5 μM. The minimum detectable concentration is 50 pM. For ECL, it showed wider linearity range over 5 nM ∼ 5 μM and lower detectable concentration of 10 pM. This indicated that the ECL assay could be comparable to the conventional electrochemical assay. Furthermore, this biosensor possesses high selectivity over different sequences of target DNA oligonucleotides.
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