Label-Free Detection of Biomolecules Using A Tapered Optical Fiber Sensor

A tapered optical fiber sensor (TOFS) is a kind of optical fiber sensor that uses special geometries to measure properties of surrounding environments or samples using evanescent waves. This paper presents a fast, highly sensitive, and inexpensive tapered optical fiber biosensor that, using a miniature sensing structure, enables the label-free direct detection of biomolecules. The sensor takes advantage of the interference effect between the fiber's first two modes along the taper waist region. This effect causes some interference fringes in the transmission spectrum. Because of its sharp spectrum fringe signals and its long biomolecule testing region, the sensor is fast and highly sensitive. To better understand the influence of various biomolecules on the sensor, a computer simulation that varied such bio-layer parameters as thickness and refractive index was performed. The result of 0.4 nm/nm showed that the spectrum fringe shift of the sensor was large enough to be easily measured even when the bio-layer was nanometers thick. A tapered optical fiber biosensor was then fabricated and evaluated with an immune globulin G (IgG) antibody-antigen pair, and showed good performance.