Biophotonics_Concepts_to_Applications

7.1 Overview of Biosensors and Probes

This chapter addresses the basic designs of opticalfiber probes and opticalfiber-based
and waveguide-based biosensor configurations that are necessary for the biomedical
optics processes described in Chaps. 8 – 11. First Sect.7.2 illustrates one-fiber,
dual-fiber, and multiple-fiber probe configurations. Depending on the probe appli-
cation, specific configurations could incorporate a number of peripheral optical ele-
ments such as opticalfilters, beam splitters, optical circulators, or alignment optics.
Next Sect.7.3describes opticalfiber tip geometries used at thedistal endof a
fiber link (i.e., the farthest point from the optical source or from thefinal signal
observation and analysis point). The tip configuration of a probe is an important
design factor for efficient light delivery and collection in any biophotonics appli-
cation. Implementations of these opticalfiber probes in biophotonics disciplines are
described in Chaps. 8 – 11.
In addition to the use of opticalfibers for delivering light to and from a diagnostic or
treatment area of a tissue, a number of opticalfiber structures have been widely
investigated and implemented for the diverse biosensing and biomedical measure-
ment functions listed in Fig.7.2. The sensing functions include detecting the presence
of specific classes of molecules or measuring the characteristics of cells, proteins,
DNA, and other biological species. These biophotonics applications are a result of
opticalfiber characteristics that include their small size andflexibility, excellent
capability for integration into photonics components and instruments, and relatively
high sensitivity of changes in the amplitude, phase, or polarization of propagating
light in response to variations in physical factors such as stress, strain, temperature, the
refractive index, andfiber movement or microbending. For example, as described in

Biological

elements

Origins of

biological samples

Biosensing devices

and methods

• Microorganisms


• Organelles


• Tissue samples


• Cells


• Enzymes


• Antibodies


• Nucleic acids
  
  
  • Human tissues/fluids
    (skin, flesh, bones, blood)
  
  
  • Animal tissues/fluids
  
  
  • Cell cultures
  
  
  • Foods
  
  
  • Components in water, air,
    soil, vegetation
    
    
    • Optical fiber probes
    
    
    • Nanoparticle-based sensors
    
    
    • Optical fiber substance sensors
    
    
    • Waveguide substance sensors
    
    
    • Photodetector arrays
    
    
    • Fiber Bragg grating sensors
    
    
    • Surface plasmon resonance
    
    
    
    
  
  
  
  

Biophotonics

sensors and probes

Fig. 7.1 Examples of biological elements, biological sample origins, and sensing devices and
methods

198 7 Optical Probes and Biosensors