Measurement of changes in concentrations of biological solutions using a Rayleigh interferometer

A Rayleigh interferometer was constructed to measure changes of concentrations in the biological solutions. With the stability tests, our Rayleigh interferometer system showed its insensitivity to environment vibrations and with the second compensating cuvette, effects on the refractive index changes other than the concentration changes of molecules in the sample solution could be compensated. A thin glass plate was inserted in the beam path and rotated to vary the optical path length to test the sensitivity of the system. With this glass plate, the detectable optical path differences of the system was Δ(nl) = 7 nm. Finally, the concentration of sucrose solutions were varied to change the refractive index. The refractive index changes by 1.43 × 10-4 for each gram of sucrose per liter at 20°C. With our system, the sensitivity to sucrose solution was 7mg/L. Based on this sensitivity this interferometric system can be used to detect concentrations of albumin solutions as low as 0.6mg/mL.

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