Biophotonics_Concepts_to_Applications

is based on observing thefluorescence emitted from a detection antibody that binds
to an absorbed antigen [ 3 ]. The key operational characteristic of this sensing
method is that the detection antibody willfluoresce at a specific excitation wave-
length, which thereby indicates the presence and concentration of an analyte. To
construct the sensor,first afiber is coated with an antibody and then is immersed in
a medium containing antigens, which are captured by the antibody layer. Next a
layer of the detection antibodies is attached to the captured antigens. This procedure
forms a sandwich structure consisting of the adhered capturing antibody layer, the
captured antigen layer, and the detection antibody layer. Once the detection anti-
bodies bind to the antigen, light sent through thefiber induces the detection anti-
bodies tofluoresce. The antigen concentration then can be determined by measuring
the degree offluorescence produced.

7.4.3 Sensors Based on Optical Fiber Movements

Some common opticalfiber-based sensors are based on measuring variations in
back-reflected light or changes in light levels coupled between twofibers [ 27 ]. The
optical power variations then can be directly correlated to changes in an external
physical parameter (e.g., pressure, stress, or temperature). One method among many
is shown in Fig.7.15. In this case, light leaving afixedfiber is coupled into a

Attached antibodies

Captured antigens

Detection antibodies

Optical fiber

Laser excitation light

Fluorescent light

Fig. 7.14 Fiber-based biosensor that uses afluorescing detection antibody attached to the antigens
(J. Biomed. Opt. 19(8), 080902 (Aug 28, 2014). doi:10.1117/1.JBO.19.8.080902)

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