Determination of nucleic acids based on shifting the association equilibrium between a heptamethine cyanine dye and poly-lysine

A near-infrared (near-IR) fluorescence recovery method for the determination of nucleic acids is presented. This method employs a two-reagent system composed of anionic heptamethines cyanine (HMC) and polycationic poly-lysine. The fluorescence of HMC, with maximum excitation and emission wavelengths at 778 and 804 nm, respectively, was quenched by poly-lysine in proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence was proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 5-300 ng mL(-1) for herring sperm DNA (FS DNA), 2-100 ng mL(-1) for calf thymus DNA (CT DNA) and 5-500 ng mL(-1) for snake ovum RNA (SO RNA). The corresponding detection limits are 1.49 ng mL(-1) for FS DNA, 0.7 ng mL(-1) for CT DNA and 1.61 ng mL(-1) for SO RNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.