December 28, 2022

Capillary-based backscattering interferometry has been used as a highly sensitive refractive index sensing tool to measure molecular binding. Generally, ray tracing is used to simulate the backscattered light from the specific capillary. Previous ray tracing models do not account for polarization effects, capillary dimensions, material choices, and other parameters that could change the interference patterns captured.  Researchers from the United Kingdom have developed a comprehensive ray tracing model including many parameters not previously reported.

The significance of the inner diameter, outer diameter, and the refractive index of the capillary material are shown to heavily influence the interference pattern. Potential designs are explored to measure sensitive temperature changes, and therefore refractive index changes, based on capillary characteristics.

Due to temperature dependence of the refractive index of the solution inside the capillary and the capillary itself, the aluminum stage that holds the capillary needs to be maintained at a stable temperature. Wavelength Electronics’ WTC3243HB temperature controller can achieve 0.0009ºC temperature stability when coupled with a Peltier thermoelectric module. This controller, an adaption of the standard WTC3243 controller, operates from 3.6 V, Lithium-Ion batteries. The WTC3243HB ensured stable refractive index of the solution inside the capillary, correlating to a more stable and repeatable backscattering light collection from the camera.  By using the WTC3243HB temperature controller, researchers were able to maintain consistent and stable temperatures of the capillary and the solution inside the capillary in this backscattering interferometer, beneficial for measuring molecular binding via interferometric refractive index sensing.

The complete case study is available as CS-TC07.

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