Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Electrical Engineering and Computer Science

First Advisor

Hyeun Joong Yoon


Fabry perot etalon, sensor, refractive index, microfluidic, hydrophilic


A new microfluidic optical biosensor was demonstrated for refractive index measurements with high sensitivity and accuracy in the range of few micrometers liquid channels utilizing a Fabry-Perot cavity formed between two reflective semitransparent surfaces. The transmitted light through the cavity forms interference peaks in the transmission spectrum which is dependent upon the refractive index of the fluid in the microfluidic channel. We demonstrate the biosensor using Fabry-Perot to provide high accuracy and sensitivity with real-time measurement. The sensor can resolve refractive index changes with the shift of peak wavelength of transmitted spectrum. In our Fabry- Perot etalon based biosensor, two thin film coated glass substrates were used to detect the biological substances in liquid. Silver thin film is used on the glass substrates as the semitransparent layer to reflect the light repeatedly and cause interference of light. The SiO2 layer coated on the silver layer created a hydrophilic surface in addition to protecting the silver layer from oxidation. The hydrophilic behavior of the SiO2 films together with a capillary action allowed the tested liquids to easily flow into and wet the cavity between the two pieces of glass substrates. The device was utilized for measurement of the refractive index of sugar, glucose, potassium and sodium solution of different concentration at room temperature. The contact angle measurer, spectrophotometer and Dektak surface profilometer were used for characterization of the sensor. The proposed sensor has high refractive index sensitivity, fast response, accurate, good linear response, and easy fabrication with super-hydrophilic microfluidic active layer. The result obtained from the experiment are in good agreement with the theoretical result and other reported result.

Library of Congress Subject Headings

Fabry-Perot interferometers.
Refractive index.


Includes bibliographical references (pages 83-90)



Number of Pages



South Dakota State University


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