Microfluidic device mixing

Fig. 2.6.11 Flow dispersion profiles obtained with (a) a capillary, (b) with a model microfluidic chip device containing a channel enlargement, directly connected to a capillary and (c) with the same microfluidic chip connected to a capillary via a small mixing volume. A sketch of the model microfluidic device is placed at the right side of each image, drawn to...

Losey MW, Jackman RJ, Firebaugh SL, Schmidt MA, Jensen KF (2002) Design and fabrication of microfluidic devices for multiphase mixing and reaction. J Microelectromech Syst 11 709-717... 

Y. Liu, D.O. Wipf and C.S. Henry, Conductivity detection for monitoring mixing reactions in microfluidic devices, Analyst, 126 (2001) 1248-1251. 

Panic, S., Loebbecke, S., Tuercke, T., Antes, J., Boskovic, D., Experimental approaches to a better understanding of mixing performance of microfluidic devices, Chem. Eng. J. 2004, 101, 409 419. 

Jacobson, S.C., McKnight, T.E., Ramsey, J.M., Microfluidic devices for electro-kinetically driven parallel and serial mixing. Anal. Chem. 1999, 71(20), 4455 1459. 

Vreeland, W.N., Locascio, L.E., Using bioinspired thermally triggered liposomes for high-efficiency mixing and reagent delivery in microfluidic devices. Anal. Chem. 2003, 75, 6906-6911. 

Figure 4 A simple y-shaped microfluidic device with two inlet channels and a single outlet channel. The device can be used to mix and react two reagents A and B. By varying the relative volumetric rates (FA and FB) at which the reagents are injected, it is possible to vary the composition of the mixture in the outlet channel. By varying the total flow rate (F=FA + FB), it is possible to control the time the reagents spend in the reaction channel.

An additional advantage of using microfluidic devices, which we do not have the space to discuss in detail here, is the absence of turbulence (Koo and Kleinstreuer, 2003). In the context of nanoparticle synthesis, turbulence gives rise to unpredictable variations in physical conditions inside the reactor that can influence the nature of the chemical product and in particular affect the size, shape, and chemical composition. In microfluidic devices, turbulence is suppressed (due to the dominance of viscous over inertial forces) and fluid streams mix by diffusion only. This leads to a more reproducible reaction environment that may in principle allow for improved size and shape control. 

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

The simple geometric metering scheme shown in Fig. 11.4 has been used to develop a highly efficient microfluidic device for protein crystallization in ultra-small volume reactions. The crystallization chip implements 144 simultaneous metering and mixing reactions while consuming only 3.0 pL of protein solution. A layout of the chip (Fig. 11.5) shows 48 reaction centers (Fig. 11.4), each consisting of three pairs of microfluidic reaction chambers with relative volumes of 1 4, 1 1 and 4 1. 

H.Y. Park, X. Qiu, E. Rhoades, J. Korlach, L.W. Kwok, W.R. Zipfel, W.W. Webb, L. Pollack, Achieving uniform mixing in a microfluidic device hydrodynamic focusing prior to mixing. Anal. Chem. 78(13), 4465-4473 (2006)... 

Yuen PK, Li G, Bau Y, Muller UY, Microfluidic devices for fluidic circulation and mixing improve hybridization signal intensity on DNA arrays. Lab Chip 2003 3 46-50. 

As demonstrated in this chapter, a number of microfluidic devices of various structures and sizes for extremely fast mixing, heat exchanging and residence time control have been developed based on conventional and modern fabrication technologies. Microflow systems composed of such microfluidic devices are expected to serve as powerful tools for conducting extremely fast, highly exothermic reactions in a highly controlled manner to effect flash chemistry, where desired products are formed within milliseconds to seconds. 

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