A fiber-optic evanescent wave DNA biosensor based on novel molecular beacons.

We have prepared a novel optical fiber evanescent wave DNA biosensor using a newly developed molecular beacon DNA probe. The molecular beacons (MB) are oligonucleotide probes that become fluorescent upon hybridization with target DNA/RNA molecules. Biotinylated MBs have been designed and immobilized on an optical fiber core surface via biotin-avidin or biotin-streptavidin interactions. The DNA sensor based on a MB does not need labeled analyte or intercalation reagents. It can be used to directly detect, in real-time, target DNA/RNA molecules without using competitive assays. The sensor is rapid, stable, highly selective, and reproducible. We have studied the hybridization kinetics of the immobilized MB by changing the ionic strength of the hybridization solution and target DNA concentration. Our result shows divalent cations play a more important role than monovalent cations in stabilizing the MB stem hybrids and in accelerating the hybridization reaction with target DNA/RNA molecules. The concentration detection limit of the MB evanescent wave biosensor is 1.1 nM. The MB DNA biosensor has been applied to the analysis of specific gamma-actin mRNA sequences amplified by polymerase chain reaction.