A fiber optic biosensor for fluorimetric detection of triple-helical DNA.

A fiber optic biosensor was used for the fluorimetric detection of T/AT triple-helical DNA formation. The surfaces of two sets of fused silica optical fibers were functionalized with hexaethylene oxide linkers from which decaadenylic acid oligonucleotides were grown in the 3'to 5'and 5'to 3'direction, respectively, using a DNA synthesizer. Fluorescence studies of hybridization showed unequivocal hybridization between oligomers immobilized on the fibers and complementary oligonucleotides from the solution phase, as detected by fluorescence from intercalated ethidium bromide. The complementary oligonucleotide, dT10, which was expected to Watson-Crick hybridize upon cooling the system below the duplex melting temperature ( T m), provided a fluorescence intensity with a negative temperature coefficient. Upon further cooling, to the point where the pyrimidine motif T*AT triple-helix formation occurred, a fluorescence intensity change with a positive temperature coefficient was observed. The reverse-Hoogsteen T.AT triplex, which is known to form with branched nucleic acids, provided a corresponding decrease in fluorescence intensity with decreasing temperature. Full analytical signal evolution was attainable in minutes.