Electrochemical Sensing of DNA Hybridization Based on Duplex-Specific Charge Compensation

Abstract

A nonlabeling voltammetric detection method for DNA hybridization has been developed, in which [Fe(CN)₆]^3- in solution can readily approach an electrode surface covered with a charge-compensated DNA duplex layer and thus provides a strong redox-sensing current. Charge compensation for negative charges on the DNA backbone has been specifically accomplished on DNA duplexes by discouraging nonspecific binding of positively charged intercalating molecules with single strands. A pretreatment of DNA-modified electrodes with sodium dodecyl sulfate before the intercalator binding process is essential in preventing the nonspecific binding. Since ferricyanide, the only electrochemically active species, is present in the voltammetric solution, the detection signal can be amplified by increasing its concentration. Combination of the duplex-specific charge compensation with the signal amplification has achieved a remarkable signal difference: in 30 mM [Fe(CN)₆]^3-, the area ratio between cyclic voltammograms of the hybridized and unhybridized electrodes is ∼200 when 3,6-diaminoacridine is used as the intercalator. High sensitivity of the method has been demonstrated by detecting 10 fM (100 zmol in amount) of a target probe DNA.