Cationic cyanine as a near-infrared fluorescent probe for the determination of nucleic acids

A new method with a cationic near-IR cyanine as fluorescent probe was devel oped for the determination of nucleic acids. The near-IR cyanine shows maxi mum excitation and emission wavelengths at 765 and 790 nm, respectively, in aqueous solution. The method is based on the fluorescence decrease of near -IR cyanine in the presence of nucleic acids. Under optimal conditions, the ratio of fluorescence intensity in the absence and presence of nucleic aci ds was proportional to the concentration of nucleic acids over the range 0. 10-1.2 mu g/mL for CT (calf thymus) DNA or SM (salmon sperm) DNA, and 0.10- 1.6 mu g/mL for yeast RNA. The detection limits were 30 ng/mL for CT DNA, 2 5 ng/mL for SM DNA and 70 ng/mL for yeast RNA. The relative standard deviat ion (n = 6) was 2.1% for 500 ng/mL CT DNA, 2.4% for 500 ng/mL SM DNA and 2. 7% for 500 ng/mL yeast RNA, respectively.