Biosensors waveguide evanescence

S. J. Lackie, T. R. Glass. M. J, Block "Instrumentation for Cylindrical Waveguide Evanescent Fluor-osensors." in D, L. Wise, L. B. Wingard (eds,) Biosensors with Fiberoptics. Humana Press, Clifton, N.J., 1991. 

Perhaps the most effective demonstration of the advantages of evanescent wave interrogation is provided by the optical biosensor platform depicted in Figure 5. The platform consists of a multimode slab waveguide on the upper surface of which antibodies have been immobilised. 

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

Sol-gel coating technique for optical chemical sensors and biosensors is now in extensive research phase. For example, the side-coating of optical fibers or waveguides in evanescent-wave sensors it is particularly important to control precisely the sensitivity determining parameters, such as the coating thickness and length45. 

Demarco D.R., Lim D.V., Detection of Escherichia coli 0157 H7 in 10-and 25-gram ground beef samples with an evanescent-wave biosensor with silica and polystyrene waveguides, J. Food Protect. 2002 65 596-602. 

Fig. 9.24 Schematic of evanescent field biosensor. The intensity of the light is attenuated by the interaction of the light with the molecules present at the surface of the waveguide...

For example, several strategies have been used for immunoassay techniques with fiber-optic biosensors. In the sandwich format, the receptor is immobilized on the stu"face of the fiber waveguide and a secondary or tracer antibody (which is labelled with a fluorescent dye) is added to the solution. In the absence of the analyte, the tracer remains in solution and little fluorescence is observed. However, after addition of the analyte, a molecular sandwich is formed on the sensor smface within the evanescent excitation volume. The sandwich assay is usually more sensitive than a competitive-binding assay because the fluorescence intensity increases with analyte concentration. 

Low detection limits of 10/xgl were established. Similar approaches for the miniaturization of SPR can be found in literature, however, similar to the miniaturized cantilever biosensor, any surface-active interfering compound in samples will cause significant analytical challenges. Borchers and coworkers used a microchip evanescent waveguide for the detection of realtime DNA hybridization events. A lower detection limit of 0.21 nmol 1 was demonstrated. The authors also showed multi-analyte detection capabilities of their system and suggested that this strategy can be utilized in real-time DNA array format with analysis times as short as 2 min. 

DeMarco DV, Lim DV (2001) Direct detection of escherichia coliol57 h7 in unpasterized apple juice with an evanescent wave sensor. J Rapid Meth Automation Micro 9 241-257 Diez A, Andres MV, Cruz JL (2001) In-line fiber-optic sensors based on the excitation of surface plasma modes in metal-coated tapered fibers. Sensors Actuators B Chem 73 95-99 Dostalek J, Ctyroky J, Homola J, Brynda E, Skalsky M, Nekvindova P, Spirkova J, Skvor J, Schrofel J (2001) Surface plasmon resonance biosensor based on integrated optical waveguide. Sensors Actuators B Chem 76 8-12... 

Keywords Absorption ARROW waveguide Biosensor Chemical sensor Confinement Dielectrics Evanescent field Fiber optics Fluorescence Hollow core Liquid-core Loss Optical mode Photonic crystal Refractive index Resolution Scattering Sensitivity Total internal reflection Waveguide... 

The fiber-optic biosensor, based on an evanescent wave, is the most popular of the biosensors using waveguides. In the early stage, a capillary is used as the waveguide to collect free... 

MEMS-Based Biosensor, Fig. 7 (a) Schematic of an evanescent wave traveling in an optical waveguide. The traveling light in the waveguide is influenced by analyte-induced changes of the refraction index in the adjacent... 

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