Total internal reflection imaging ellipsometry (TIRIE) is widely used in the field of the biological detection due to its high sensitivity and multi-detection capability. Traditionally, the ellipsometric measurement works under the null-off null condition which is insensitive to the small interface variations such as the electron density disturbance at the sensing surface. Thus, we analyze the response of the detected signals under the different working conditions to the ellipsometric parameter variations and optimize the polarization settings to further enhance the TIRIE response to the subtle interface variation in this paper. Furthermore, the relationship between the detected signal and the electron density disturbance is obtained, and the result shows that the detection sensitivity for the subtle interface changes is improved by one hundred times under the optimized working condition.
Our previous work has proposed an electrochemistry - total internal reflection imaging ellipsometry (EC-TIRIE) technique to observe the dissolved oxygen (DO) reduction on Clark electrode since high interface sensitivity makes TIRIE a useful tool to study redox reactions on the electrode surface. To amplify the optical signal noise ratio (OSNR), a surface tethered weak polyelectrolyte, carboxylated poly(oligo(ethylene glycol) methacrylate-random- 2-hydroxyethylmethacrylate) (abbreviated as carboxylated poly(OEGMA-r-HEMA)), has been introduced on the electrode surface. Since Clark electrode is widely used in biochemical oxygen demand (BOD) detection, we use this technique to measure BOD in the sample. The dynamic range of the system is from 0 ∼ 25 mg/L. Two samples have been measured. Compared with the conventional method, the deviation of both optical and electrical signals are less than 10%.
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