We report U-shaped biconically tapered optical fibers (BTOF) as dip probes for label-free immunoassays. The tapered
regions of the sensors were functionalized by immobilization of immunoglobulin-G (Ig-G) and tested for detection of
anti-IgG at concentrations of 0.5, 5.0, and 50 μg/mL. Antibody-antigen reaction creates a biological nanolayer
modifying the waveguide structure leading to a change in the sensor signal, which allows real-time monitoring. The
kinetics of the antibody (mouse Ig-G) -antigen (rabbit anti-mouse IgG) reactions was studied. The limit of detection for
the sensor was estimated to be less than 0.5 μg/mL with low temperature sensitivity. Utilization of the rate of the sensor
peak shift within the first few minutes of antibody-antigen reaction is proposed as a rapid detection method.