Our study examines the transmission characteristics of bi-tapered optical fibers, i.e. fibers that have a tapered down and up span with a waist length separating them. The applications to aqueous and vapor phase biomolecular sensing demand high sensitivity. A bi-tapered optical fiber platform is suited for label-free biomolecular detection and can be optimized by modification of the length, diameter and surface properties of the tapered region. We have developed a phase sensitive method based on interference of two or more modes of the fiber and we demonstrate that our fiber sensitivity is of order 10<sup>-4</sup> refractive index units. Higher sensitivity can be achieved, as needed, by enhancing the fiber design characteristics.
Our research demonstrates the design and fabrication of a biosensor based on the tapered optical fiber. The fiber is
tapered biconically to a diameter of approximately 7 μm, which allows the evanescent field of propagating light to
interact with molecules attached to the tapered surface. This sensing platform is capable of fast, continuous, specific,
sensitive, and label-free molecular detection in the aqueous phase. Detection is demonstrated across multiple fibers, and
the individual fibers are reusable. The system described previously has been modified for detection of volatile organic
compounds. The fabrication of the modified design is also shown with preliminary results.
This study focuses on the design, fabrication and characterization of a tapered optical fiber platform for the label-free detection of aqueous and gaseous biomolecules. Single mode fibers were tapered to a diameter of approximately 10 microns, and this tapered surface was functionalized with biomolecules for aqueous (antibody) detection of analytes. Molecular binding to the surface changes the refractive index and thickness of the biolayer, which interacts with propagating light, causing a measureable phase shift in the output.