Development of interferometer for refractive index measurement of aqueous solution in a microfluidic chip

This study presents the design and development of an interferometer for the measurement of the refractive index or concentration of a sub-microliter volume of aqueous solution in a microfluidic chip. This proposed interferometer is manifested by the successful measurement of the refractive index of a sugar–water solution, using a He–Ne laser as a light source and robust instrumentation for practical implementation. The measurement principle and the feasibility of the system are analyzed theoretically. The experimental device is constructed with a He–Ne laser, two lenses, two optical plates and a complementary metal oxide semiconductor detector. The refractive index change is determined by measuring the positional changes of the interference fringes. A refractive index change of 10−4 is inferred from the measured image data. (letter)