Linear sweep polarographic determination of nucleic acids using acridine orange as a bioprobe

The interaction of acridine orange (AO) with double-stranded (ds) DNA in aqueous solution was investigated by linear sweep polarography (LSP) on a dropping mercury working electrode (DME). In pH 2.5 Britton-Robinson (B-R) buffer solution, AO had a sensitive linear sweep polarographic reductive peak at -0.89 V (vs. SCE), which could be greatly inhibited by the addition of dsDNA, with a positive shift of the peak potential. Based on the decrease of the reductive peak current, a new quantitative electrochemical determination method for dsDNA was developed with a linear range of 2.0−20.0 mg l -1 and the linear regression equation: ∆Ip" (nA) = 111.90 C (mg l -1 )+125.32 (n = 9, γ = 0.997). The influences of com- monly co-existing substances, such as metal ions, amino acid, etc., on the determi- nation were also investigated. The method is sensitive, rapid and simple with good selectivity. The new proposed method was further applied to the detection of RNA and three synthetic samples containing dsDNA with satisfactory results. The bin- ding number and the equilibrium constant between dsDNA and AO were calculated by an electrochemical method.