Submillisecond mixing in a continuous-flow, microfluidic mixer utilizing mid-infrared hyperspectral imaging detection

• Type of Material: Article
• Authors: Drew P. Kise, Emory University; Donny Magana, Emory University; Michael Reddish, Emory University; Richard Dyer, Emory University
• Language: English
• Date: 2014-02-07
• Publisher: Royal Society of Chemistry
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2014 The Royal Society of Chemistry.
• Final Published Version (URL): http://dx.doi.org/10.1039/c3lc51171e
• Title of Journal or Parent Work: Lab on a Chip
• ISSN: 1473-0197
• Volume: 14
• Issue: 3
• Start Page: 584
• End Page: 591
• Grant/Funding Information: This work was supported by NIH grants GM53640 and GM068036 (RBD) and by an NSF graduate fellowship DGE-0940903 (MJR).
• Keywords: Time Factors; Adenosine Monophosphate; Models, Theoretical; Deuterium Oxide; Spectrophotometry, Infrared; Microfluidic Analytical Techniques; Water
• Research Categories: Engineering, Biomedical; Biology, Molecular; Biophysics, General

Abstract

We report a continuous-flow, microfluidic mixer utilizing mid-infrared hyperspectral imaging detection, with an experimentally determined, submillisecond mixing time. The simple and robust mixer design has the microfluidic channels cut through a polymer spacer that is sandwiched between two IR transparent windows. The mixer hydrodynamically focuses the sample stream with two side flow channels, squeezing it into a thin jet and initiating mixing through diffusion and advection. The detection system generates a mid-infrared hyperspectral absorbance image of the microfluidic sample stream. Calibration of the hyperspectral image yields the mid-IR absorbance spectrum of the sample versus time. A mixing time of 269 μs was measured for a pD jump from 3.2 to above 4.5 in a D2O sample solution of adenosine monophosphate (AMP), which acts as an infrared pD indicator. The mixer was further characterized by comparing experimental results with a simulation of the mixing of an H 2O sample stream with a D2O sheath flow, showing good agreement between the two. The IR microfluidic mixer eliminates the need for fluorescence labeling of proteins with bulky, interfering dyes, because it uses the intrinsic IR absorbance of the molecules of interest, and the structural specificity of IR spectroscopy to follow specific chemical changes such as the protonation state of AMP.