Passive Helical Micromixer for Lab-on-a-Chip and Biomicrofluidics Applications

Passive micromixing is of considerable importance in many biomicrofluidic devices and lab-on-a-chip bioanalysis systems, as microscale reactions carried out in such platforms require on-chip mixing of microliter-scale samples of liquids and reagents. Passive micromixing techniques primarily rely on microchannel geometry to promote fluid mixing by folding and stretching fluid streams, thereby increasing the interfacial area over which diffusion occurs. Due to the small geometric scales of the channels and low Reynolds numbers (Re), inertial forces are much smaller than viscous forces, and the fluid flow is typically laminar in these systems. This low-Re regime poses a significant challenge for efficient mixing, as turbulence is absent and mixing must rely predominantly on diffusion, which is very slow in these systems. To overcome this limitation, we utilize a helical mixer chip with an "X"-shaped coil-like design to enhance diffusion and promote efficient mixing. The helical design allows two fluid streams to be mixed and then split into separate streams for further processing. The helical-style micromixer is integrated with a microfluidic platform equipped with a flow control system composed of two valves and two syringe pumps, delivering fluids at a controlled flow rate. Mixing performance is characterized using a synchronized inverted fluorescence microscope, enabling real-time visualization of fluid interdiffusion. A fluorescence intensity probe is employed to assess concentration distribution and quantify mixing efficiency at various locations along the helical coil.