Abstract
Functionalized sensor surfaces combined with microfluidic channels are becoming increasingly important in realizing efficient biosensing devices applicable to small sample volumes. Relaxing the limitations imposed by laminar flow of the microfluidic channels by passive mixing structures to enhance analyte mass transfer to the sensing area will further improve the performance of these devices. In this paper, we characterize the flow performance in a group of microfluidic flow channels with novel double curved passive mixing structures (DCMS) fabricated in the ceiling. The experimental strategy includes confocal imaging to monitor the stationary flow patterns downstream from the inlet where a fluorophore is included in one of the inlets in a Y-channel microfluidic device. Analyses of the fluorescence pattern projected both along the channel and transverse to the flow direction monitored details in the developing homogenization. The mixing index (MI) as a function of the channel length was found to be well accounted for by a double-exponential equilibration process, where the different parameters of the DCMS were found to affect the extent and length of the initial mixing component. The range of MI for a 1 cm channel length for the DCMS was 0.75–0.98, which is a range of MI comparable to micromixers with herringbone structures. Overall, this indicates that the DCMS is a high performing passive micromixer, but the sensitivity to geometric parameter values calls for the selection of certain values for the most efficient mixing.
Highlights
Integration of microfluidics and microfluidic channels within several scientific domains have increased over the past few decades
The results on the mixing index (MI) and the initial rate of mixing for a newly fabricated passive ceiling mixing structure group show a large dependence on the geometry of the structure
The addition of a second curved structure to the previously studied curved mixing structure (CMS) group [56] resulting in the novel double curved mixing structure (DCMS) had a drastic effect on the flow pattern induced by the mixers and the resulting efficiencies
Summary
Integration of microfluidics and microfluidic channels within several scientific domains have increased over the past few decades This merger has led to the development of devices such as Lab-on-Chip, Organ-on-Chip, and sensors for the determination of various biological, chemical, and medical analytes, as well as applications as reactors [1,2,3,4]. One of the major disadvantages is the laminar flow regime encountered for fluid flow at the microscale. This reduces the impact of inertial forces over the viscous forces and yields low Reynold’s numbers. With a laminar flow, the only mixing that occur is by diffusion, which is a relatively inefficient mixing process This limitation of laminar flows has led to the development of different mixing techniques to enhance the rate of mixing. The various fluid mixing strategies are grouped into processes referred to as either active or passive, where the active mixers require external energy input
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