Amplified voltammetric detection of DNA hybridization via oxidation of ferrocene caps on gold nanoparticle/streptavidin conjugates.

Gold nanoparticle/streptavidin conjugates covered with 6-ferrocenylhexanethiol were attached onto a biotinylated DNA detection probe of a sandwich DNA complex. Due to the elasticity of the DNA strands, the ferrocene caps on gold nanoparticle/streptavidin conjugates are positioned in close proximity to the underlying electrode modified with a mixed DNA capture probe/hexanethiol self-assembled monolayer and can undergo reversible electron-transfer reactions. A detection level, down to 2.0 pM (10 amol for the 5 microL of sample needed) for oligodeoxynucleotide samples was obtained. The amplification of the voltammetric signals was attributed to the attachment of a large number of redox (ferrocene) markers per DNA duplex formed. The ferrocene oxidation current increased with the target concentration and began to level off at a target concentration of 10 nM. An Excellent linearity was found within the range between 6.9 and 150.0 pM and reasonable relative standard deviations (between 3.0 and 13.0%) were obtained. The amenability of this method to the analyses of polynucleotides (i.e., PCR products of the pre-S gene of hepatitis B virus in serum samples) was also demonstrated. The method is shown to be simple, selective, reproducible, and cost-effective and does not require labeling of the DNA targets.