Highly sensitive refractive index measurement with a sandwiched single-flow-channel microfluidic chip

Abstract

We propose a simple single-flow-channel microfluidic chip that can be used in an interferometry-based refractometer for the realization of highly sensitive refractive index analysis. The key idea relies on sandwiching two single-flow-channel microfluidic chips in such a way that their flow channels are laterally shifted with respect to each other, forming two flow channels for use in our Young’s interferometric-based refractometer. Experimental demonstrations on our laboratory prototype, comprised of two large 1 mm deep single-flow-channel microfluidic chips with a 400 μm lateral shift between the two flow channels, a 635 nm wavelength laser diode, and a 1600 × 1200 pixel image sensor, show a very high measured sensitivity of 5.62 × 10⁻⁶ RIU/pixel with a measured resolution of 9.67 × 10⁻⁷ RIU when used to determine the refractive indices of phosphate buffered saline solutions. Additional key features include a low component count, high compactness, and ease of implementation.