Digital microfluidic systems

Pair, P., Pamula, V. K., Fair, R. B., Rapid droplet mixers for digital microfluidic systems, Lab Chip 2003, 3, 253-259. 

R.-F. Yue, J.-G. Wu, X.F. Zeng, M. Kang, and L.T. Liu, Demonstration of four fundamental operations of liquid droplets for digital microfluidic systems based on an electrowetting-on-dielectric actuator. Chin. Phys. Lett. 23, 2303-2306 (2006). 

L. Luan, R.D. Evans, D. Schwiim, R.B. Fair, and N.M. Jokerst, Chip scale integration of optical microresonator sensors with digital microfluidics systems, LEOS-2008, Newport Beach, CA, Nov. 9-13 (2008). 

MALDI-TOF-MS has been demonstrated as a useful tool in pre-steady state kinetic research by Houston et al., who combined it off-line with quench-flow methods to follow the appearance of a protein tyrosine phosphatase (PTPase) reaction intermediate.12 Houston et al. were able to measure rate constants up to 30 s 1, with k2/k3 ratios up to approximately 15. The device described in this chapter extends this technique to measure rate constants approximately 5 times greater, with k2/k3 ratios approximately twice previously measurable values. MALDI-TOF-MS is typically conducted on a centimeter-scale conducting plate the digital microfluidic system employed is a square plate approximately 2 cm on each side, with 16 experimental units per chip, which can be placed directly inside a standard MALDI-TOF-MS plate that has been machined appropriately. By grounding the exposed wires on the otherwise insulated chip, charging is negligible. 

We have also performed a colorimetric experiment with DNT in DMSO and KOH in DI water on the same electro wetting chip. However, we have not performed quantitative measurements nor determined the stability of the reaction. Further experiments are needed to assess the stability of the reaction and establish the linear range of detection for DNT. Also, experiments need to be performed on nitroaromatic samples extracted from soil and for samples in water to establish the suitability of a digital microfluidic system for field screening of nitroaromatics. 

A digital microfluidic system based on the BCD is demonstrated in Fig. 5. The array of electrodes is simply made by assembling three pin header sockets (2x5 pins with 2.54 mm pitch, < 0.1) which are commonly used in conventional electronics. To prevent leakage of a suspending medium and falling of droplets between electrodes, polydimethylsUoxane (PDMS) is used to... 

Fig. 5 A digital microfluidic system based on the BCD actuation and the demonstration on the translational motion of a 300 liL droplet across the array of electrodes by polarity control under 300 V...

K.P. Nichols, H. Gardeniers, A digital microfluidic system for the investigation of pre-steady-state enzyme kinetics using rapid quenching with MALDI-TOF mass spectrometry. Analytical Chemistry, 2007, 79, 8699-8704. 

Rapid Droplet Mixers for Digital Microfluidic Systems. Lab Chip, 2003, 253-259. 

Nichols, K.P., Gardeniers, H.J.G.E. (2007) A Digital Microfluidic System for the Investigation of Pre-steady-state Enzyme Kinetics Using Rapid Quenching with MALDI-TOF Mass Spectrometry. Anal. Chem. 79 8699-8704. 

Disadvantages of conventional microchips include resistance to hydrodynamic flow (backpressure), adsorption of some biomolecules on walls, and limited robustness (e.g., clogging narrow channels). Digital microfluidic systems overcome the problems with mixing reagents, which are normally associated with conventional microfluidic devices that use laminar hydrodynamic flow. Such microscale platforms are normally based on the electrowetting-on-dielectric (EWOD) principle [66]. In these digital microchips. 

This phenomenon is known as electrowetting. A hydrophobic surface like Teflon can behave like a hydrophilic surface due to the application of electric potential. Electrowetting can be used for the creation, transportation, and merging of droplet for digital microfluidic systems. Electrowetting can also be used in micromixers. 

The digital microfluidic system has the following overall benefits ... 

No moving parts There is no requirement of valves and pumps in the digital microfluidic systems. 

Cho SK and Kim CJ 2003 Particle separation and concentration control for digital microfluidic systems. 

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