Label-free detection of DNA hybridization by using charge perturbation on poly(thionine)-modified glassy carbon and gold electrodes

Simple and label-free electrochemical sensors for the detection of DNA hybridization were developed based on charge perturbation of poly(thionine)-modified glassy carbon and gold electrodes (PTH/GCE and PTH/Au). Probe DNA (pDNA) was immobilized on PTH films via covalent bonds between the amine (-NH₂) group of the PTH and the phosphate (PO₄^3-) group at the 5′ end of the pDNA. The immobilized single-strand pDNA decreased the oxidation current of [Fe(CN)₆]^4- as a result of electrostatic repulsion by the negatively charged PO₄^3- backbone of the pDNA. The current was further decreased subsequent to duplex formation by the hybridization of target complementary DNA (cDNA) due to increased electrostatic repulsion. Both sensors demonstrated excellent selectivity, stability, and the sensitivity of 1.27 and 58.6 μA · cm^-2 · pM^-1 with detection limits of 0.47 and 0.20 pM, respectively, for cDNA hybridization.