Built-in-mask microfluidic chip for highly-sensitive Young interferometry-based refractometer structure

In this article, we propose a built-in-mask two-flow-channel microfluidic chip for use in our highly-sensitive Young interferometry-based refractometer structure. Our key idea is to make the area surrounding the two flow channels opaque by using a black material (e.g., black silicone). Once the incoming optical beam passes through the two flow channels, it is automatically divided into two optical beams that will interfere with each other at the two-dimensional detection plane, eliminating a highly precise alignment technique previously required between an external mask and the microfluidic chip. Experimental proof of concept using a two-flow-channel microfluidic chip with a channel spacing and depth ratio of 3, a 635-nm wavelength laser diode, and a 1600×1200-pixel image sensor shows a measured high 4.28×10^-5 RIU/pixel sensitivity with a measured resolution of 8.11×10^-6 RIU.