Refractive index measurements in a shallow multichannel microfluidic system

Thin film interference of monochromatic radiation in transparent films is used extensively as a non-destructive technique to determine film thickness over extended surface areas. This approach may also be used with liquids where reflection at solid/liquid/solid interfaces creates an interference pattern, dependent on the liquid refractive index. Such a system facilitates refractive index measurements in low volume (nanolitre) samples, without the need for high-index structured materials forming waveguide layers. We use a planar multichannel microfluidic device fabricated with a standard photolithography technique and demonstrate its suitability for nanolitre refractive index measurements. Liquids of varied refractive indices from 1.33 to 1.35 were evaluated in the microfluidic channel, indicating a limit of detection 10 ^-6 refractive index unit (RIU), illustrating how this approach can simultaneously monitor a number of transparent and weakly absorbing liquid samples.