Extremely sensitive methods that also show a very high degree of specificity are needed today in biological, medical, and environmental arenas for detecting biomolecular and molecular analytes at concentrations below 10- 12M. Because of the enormous varietv of base sequences possible, the nucleic acids present a particular challenge. The goal of the proposed research is to design and build a device that can quickly detect a desired sequence of bases in minute quantities of nucleic acid fragments. A novel biosensor will be constructed capable of determining when a DNA probe has correctly hybridized to an oligonucleotide bound to the biosensor. The probe will be labeled with a fluorophore that reacts in the near infrared. The use of fiber optics to help form the biosensor will permit a small portion of radiant energy to be refracted through the fiber core. This energy, known as an evanescent wave, will be absorbed and cause emission from the fluorophore. An optical-fiber, laser-based Mach-Zehnder interferometer, operatin$ in the near-infrared region, will determine whether a phase shift has occurred between the laser beam in the test optical fiber compared to the same beam in a reference optical fiber. Optical shifts as small as 10-6 radians can be detected with this instrument configuration. The biosensor attached to the interferometer theoretically may be capable of detecting about 3 x 10-21 mole of analyte (molecular weight of 15,000 Daltons). The biosensor could also use ribosomal RNA (rRNA) to detect specific base sequences. rRNA sequences have already been used to determine phylogenetic relationships among bacteria. The sensitivity of the proposed instrument may be sufficient to correctly identify a specific bacterial strain from the rRNA of just a single cell. The biosensor could also be important for DNA sequencing studies.Awardee's statement of the potential commercial applications of the research:Biosensors have a wide variety of applications, ranging from patient home use to process monitoring, quality control, environmental detection, and national security. The global market for biosensors is expected to rwach $750 million by the year 2000. Projections of the domestic market for biosensors indicate $69 million in sales for 1993. General and clinical laboratory requirements for biosensors have been incorporated into the design of the instrumentation developed for this proposal.National Institute of General Medical Sciences (NIGMS)
