Electrochemical DNA Biosensor Based on a Thionine-Carbon Nanotube Modified Electrode

Immobilization of DNA onto carbon nanotubes plays an important role in the development of new types of DNA biosensors. Herein, DNA biosensors based on thionine-carbon nanotube modified glassy carbon electrode is shown to be suitable for detecting a trace level of target DNA. Attachment of thionine molecules onto the sidewalls of multiwalled carbon nanotubes is accomplished via the pi-pi stacking force. Such treatment can significantly solubilize multiwalled carbon nanotubes in aqueous solution; at the same time, it functionalizes the multiwalled carbon nanotubes with rich NH2 groups. Therefore, thionine acts as a bridge to connect phosphate group terminated probe DNA with thionine-carbon nanotube modified electrodes through the phosphoramidate bond. After the DNA hybridization process, the interaction between daunomycin and double stranded DNA molecules immobilized on the modified electrode can be observed obviously by differential pulse voltammetry, which is used as a hybridization detection signal. Modification of the electrode with thionine-carbon nanotubes significantly enhances the amount of captured DNA and promotes electron transport; therefore, a substantial lowing of the detection limit is obtained compared with conventional electrodes.