Fluorometric determination of deoxyribonuclease I activity with PicoGreen

A rapid and sensitive assay for the detection of deoxyribonuclease I (DNase I) activity is described. This method is based on the ability of PicoGreen dye to enhance its fluorescence when bound to double-stranded DNA. In the standard assay, reaction mixtures containing the DNase I sample and 0.2 microg of the substrate DNA were prepared in a fluorescence microtiter plate and incubated at 37 degrees C. At the end of the reaction, the diluted PicoGreen reagent was added to each well and fluorescence intensity was measured with a fluorescence plate reader. By this assay, it was possible to determine precisely as little as 5 pg of DNase I within an hour. Moreover, using a small amount of the substrate DNA, the method was shown to be suitable for the sensitive detection of DNase I inhibitor activity.