Highly sensitive detection of DNA using an electrochemical DNA sensor with thionine-capped DNA/gold nanoparticle conjugates as signal tags

A highly sensitive electrochemical DNA (E-DNA) sensor based on the voltammetric detection of thionine, which was capped on diblock DNA/gold nanoparticle (DiDNA/AuNP) conjugates, on a gold electrode was developed. The E-DNA sensor was prepared through the self-assembly of a 3 '-end thiolated probe DNA (PDNA) on a gold electrode followed by the hybridization of thionine-capped DiDNA/AuNP conjugates to the 5 '-end of the PDNA. The thionine-capped DiDNA/AuNP conjugate was acted as a tag. In the absence of the target DNA, the flexible single-stranded PDNA supports an efficient contact between tag and electrode, ensuring high current of the E-DNA sensor. Upon hybridization, a rigid probe-target duplex is formed, which pushes the tag away from the electrode and increases the distance between the tag and the electrode, thereby decreasing the current of the E-DNA sensor. The analytical method based on this concept is highly sensitive because the thionine-capped DiDNA/AuNP conjugate contains a large number of electroactive thionine molecules. Under optimal conditions, the dynamic detection range of the target DNA was from 1.0 pM to 100 pM, and the detection limit was 0.5 pM. The DNA sensor also exhibited selectivity against single-base mismatched DNA. (C) 2013 Elsevier B.V. All rights reserved.