We report on a new ultrasensitive and fast technique for the detection and identification of both DNA and RNA with sensitivity of a few molecules. The new method is based on a patterned capillary tube (PCT) in which the internal surface of a glass tube is patterned with rings of different single-stranded DNA probes. A solution containing single-stranded analyte flows through the tube. Upon hybridization of appropriate DNA and RNA from the solution, DNA polymerase and reverse transcriptase (RT) are employed to synthesize the complementary nucleic acids with deoxynucleoside triphosphate (dNTP) labeled with fluorophores. The sample-analyte hybrids are detected by their fluorescence signal. We show that the new method is sensitive, is specific, can detect simultaneously both DNA and RNA from the same sample, and allows detection of analytes in serum.