Evanescent wave characteristics, optical

Love WF, Button LJ, Slovacek RE (1991) Optical characteristics of fiberoptic evanescent wave biosensors theory and experiment. In Wise LB, Wingard DL (eds) Biosensors with fiberoptics. Humana, New Jersey, pp 139-180... 

Essentially, the in vitro spectroscopic experiment involves positioning a membrane of known thickness in contact with the horizontal IRE, above which the test formulation is applied via a trough. The spectrophotometer then records the appearance of the permeant/vehicle (any diffusant with a unique IR signal) as it diffuses towards the crystal-membrane interface and into the zone accessed by the evanescent wave. This distance within the membrane at which the diffusant is monitored is defined by the optical characteristics of the IRE and membrane, being usually on the order of 1 pm. The IR absorbance increases with time as the permeant concentration rises, finally plateauing as membrane saturation is approached. The time dependence of the diffusant IR absorbance can then be analyzed using a Eickian diffusion model, yielding, for a membrane of known thickness (L) the diffusion coefficient (D), or for a membrane of unknown thickness (such as the SC) a composite parameter D/L in addition, the relative membrane solubility is obtained from the plateaued absorbance. 

Loev, W. F., Button, L. J., Slovacek, R. E. (1991) Optical Characteristics of Fiberoptic Evanescent Wave Sensor Theory and Experiment, Biosensor with Fiberoptics, the Humana Press Inc., pp.l39... 

Evanescent wave microscopy has already yielded a number of contributions to the fields of micro-and nanoscale fluid and mass transport, including investigation of the no-slip boundary condition, applications to electrokinetic flows, and verification of hindered Brownian motion. With more experimental data and improvements to TIRE techniques, the accuracy and resolution of these techniques are certain to improve. Areas of potential improvements include development of rmiform-sized and bright tracer particles, creation of high-NA imaging optics and high-sensitivity camera systems, and further development of variable index materials for better control of the penetration-depth characteristics. 

---