Simple interferometer for evanescent field refractive index sensing as a feasibility study for an immunosensor.

Area of Science:

• Optoelectronics
• Biomedical Sensing
• Optical Physics

Background:

• Optical waveguides generate evanescent fields that extend beyond their surface.
• Changes in the local refractive index near the waveguide surface can alter the evanescent field.
• This phenomenon can be harnessed for sensitive detection methods.

Purpose of the Study:

• To demonstrate a fiber optic interferometric sensor for measuring refractive index changes on waveguide surfaces.
• To explore the potential of evanescent field interactions for biosensing applications, such as immunoreactions.
• To develop the theoretical framework for understanding the sensor's sensitivity.

Main Methods:

• Utilized a Mach-Zehnder interferometer configuration.
• Incorporated a flow-through cuvette with a decladded multimode glass fiber (0.6-mm diameter, 2-cm interaction length).
• Employed modal and geometrical ray descriptions for theoretical analysis.

Main Results:

• Achieved a resolution of 1 x 10^-3 in measuring refractive index changes.
• Demonstrated the sensor's capability to detect surface refractive index variations.
• Developed a theoretical model explaining the sensor's sensitivity.

Conclusions:

• Fiber optic evanescent field sensors offer a highly sensitive method for detecting refractive index changes.
• This technology has potential applications in label-free biosensing and diagnostics.
• The developed theoretical models provide a basis for sensor optimization.