We propose a universal fluorescence method for detection of nucleic acids based on rolling circle amplification (RCA) combined with a magnetic DNA machine and using dengue virus nucleic acids as an example target. RCA specifically amplifies the target and yields a large number of initiators employing heat-labile double-stranded DNase. The magnetic DNA machine produces a fluorescence signal and eliminates background noise. This method achieved a wide linear range, promising recovery and ultrahigh recognition specificity for one-base mismatches, and indicates the potential application of this sensing strategy in the clinical diagnosis of nucleic acids of pathogens.