Fully distributed fiber-optic biological sensing

Fully distributed fiber-optic biological sensing is demonstrated based on a traveling long-period grating (LPG) in a single-mode fiber coated with a functional film. The temporal LPG is generated by an acoustic pulse propagating along the fiber. Immunoglobulin G (IgG) is immobilized onto the surface of the fiber via ionic self-assembly. We show that specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the traveling LPG when it passes through the 10-cm pretreated fiber segment. It is also shown that nonspecific binding to other unintended IgG can be avoided by the application of a standard binding block in the sensor fabrication. The experimental result proves that the traveling LPG-based fiber sensing method offers an attractive means for fully distributed bio sensing. This method may also permit measurement of other quantities that can shift the transmission spectrum of the traveling LPG by changing the properties of the fiber itself or by the assistance of a functional coating on the surface of the fiber.