An interfacial capacitance measurement electrochemical technique has been used for the sensing of self-assembled DNA hairpin probes (M. tuberculosis and B. anthracis) attached to Au electrodes. The double-layer capacitance ( ) was determined with electrochemical perturbations from 0.2？V to 0.5？V versus Ag/AgCl at a Au/M. tuberculosis DNA hairpin probe at surface coverage Au electrodes. The capacitance study was done at pH 7, which was necessary to maintain the M. tuberculosis and B. anthracis DNA probes closed during the electrochemical perturbation. Detailed experimental analysis carried out by repetitively switching the electrochemical potential between 0.2 and 0.5？V (versus Ag/AgCl) strongly supports the use of capacitance measurements as a tool to detect the hybridization of DNA targets. A large change in the capacitance deference between 0.2 and 0.5？V was observed in the DNA hybridization process. Therefore, no fluorophores or secondary transducers were necessary to sense a DNA target for both DNA hairpins. 1. Introduction The behavior of DNA attached onto metallic and nonmetallic surfaces via self-assembly with various chemistries (e.g., Au-S) may have applications in biomedical devices. For example, single-stranded DNA (ssDNA) self-assembled on a metallic interface such as gold [1, 2] or on nonmetals such as carbon nanotubes [3] and diamond [4–6] has potential use in DNA microarrays [7]. In addition, detection of DNA hybridization has been possible with techniques using different types of reporting, including fluorescence [8–11], chronocoulometry [12–14], surface plasmon resonance (SPR) [15, 16], colloidal labeling [17–19], and polarization modulation infrared reflection absorption spectroscopy [20]. Electroactive molecules can also be used to monitor the electron transfer mechanism during the hybridization process [21]. Here, we present a nonfaradaic electrochemical method based on capacitive measurement to sense DNA hairpin modification and hybridization. A nucleic acid probe has been developed to recognize specific DNA targets in solution [22]. These probes, called molecular beacons, are DNA hairpins with a fluorophore-quencher pair, which is completely unable to fluoresce when the two components are in close proximity (i.e., closed molecular beacon). When the molecular beacon spontaneously changes its conformation (like during hybridization), the fluorophore attached to one end of the molecule is no longer quenched as the quencher moves away. The capacity of this DNA hairpin has shown to discriminate between alleles with high specificity when
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