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【导师姓名】G. W. Whitesides
【研究方向】此人属于超级大牛，涉足领域极广，与分析相关的方向是Microfluidics
【所在单位】Harvard
【研究成果】

Microfluidics
The Whitesides Group is very active in microfluidics. Our previous accomplishments in the field include work on laminar flow in microchannels (Figures 1,2), fabrication of three-dimensional channel topologies (Figures 3) and mixing by chaotic advection (Figure 4). We have also applied microfluidics to fabricate monodisperse polymer, hydrogel, and metal microparticles coated with thin, nylon-coated membranes (Figure 5). Currently, we are working on several projects related to microfluidics, including exploiting the behavior of bubbles and droplets for mixing and other applications, manipulating samples electrokinetically and probing the use of solder as electrodes in microchannels.

Bubbles and Droplets in Microchannels

Our recent experiments in microfluidics include investigations into the behavior of bubbles and droplets in microchannels. Specifically, we are interested in four sub-areas: (1) enhanced mixing in microfluidic systems using bubbles; (2) the paths from monodisperse to chaotic bubbling in flow-focusing devices; (3) the production of bubbles with uniquely high periodicities in modified flow-focusing systems; (4) the path-selection process that bubbles demonstrate as they move through a network. Mixing in microchannels, in particular, is an important challenge in the microfluidics subgroup of our laboratory (the other areas introduced here are described further in the complexity section of the website).

Mixing between streams of fluid that flow in a laminar fashion is difficult to achieve. Previously, we have introduced a method to enhance mixing involving multiple lithographic steps. Our current work uses bubbles to facilitate the folding over of streams of fluid as they proceed through a network of microchannels (Movie 6). The bubbles partially block the channels in which they move, causing a portion of a stream of bulk fluid to cross over into the channel in which the other stream moves. This process is repeated several times before the streams are mixed fully, with the final mixing device occupying an area of only a square millimeter on the chip.

Electrokinetic Flow in Microfluidic Channels

We are exploring electrokinetically-driven microfluidic systems for separation of complex biological samples. Our ultimate goal is to provide a new sample handling method (femtomole/nL) for proteomic analysis and high-throughput biochemical assays. Currently, we are investigating geometrical designs, surface coatings and concentration techniques such as isotachophoresis.

TWIST Valves

We have developed a new approach for controlling the flow of fluids in microfluidic channels. TWIST valves consist of small machine screws (500 um diameter) embedded in a layer of polyurethane cast above microfluidic channels fabricated in poly(dimethylsiloxane) (PDMS). The polyurethane is cured photochemically with the screws in place; on curing, it bonds to the surrounding layer of PDMS and forms a stiff layer that retains an impression of the threads of the screws (Figure 7). The valves are separated from the ceiling of microfluidic channels by a layer of PDMS, and are integrated into channels using a simple procedure compatible with rapid prototyping. Turning the screws actuates the valves by collapsing the PDMS layer between the valve and channel, controlling the flow of fluids in the underlying channels. These valves have the useful characteristic that they do not require power to retain their setting (on/off). They also allow settings between "on" and "off", resist large back pressures (>350 kPa) without failure, and can be integrated into portable, disposable microfluidic devices for carrying out biological assays (Figure 8).

TWIST Pumps

We have designed a system for storing and pumping fluids in microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS) using TWIST valves. The method uses valves to isolate microfluidic reservoirs that are filled with solutions of reagents under pressure; the fluid is released, and the flow rate controlled, by opening one of the valves. Figure 9 shows a microfluidic pump fabricated using this approach.

References

1. Jeon, N. L. et al. "Generation of Solution and Surface Gradients Using Microfluidic Systems", Langmuir, 2000, 16, 8311-8316.

2. Wu, H. et al. "Fabrication of Topologically Complex Three-Dimensional Microstructures: Metallic Microknots" J. Am. Chem. Soc., 2001, 122, 12691-12699.

3. Stroock, A. D. et al. "Chaotic Mixer for Microchannels" Science, 2002, 295, 647-654.

4. Xu, S. et al "Generation of Monodisperse Particles by Using Microfluidics: Control over Size, Shape, and Composition" Angewandte Chemie 44 (5), 2005, 724-728.

5. Weibel, D. B. et al. "Torque-Actuated Valves for Microfluidics" Analytical Chemistry 77(15); 4726-4733, 2005.

【联系地址】gwwhitesides@gmwgroup.harvard.edu
http://gmwgroup.harvard.edu/
http://gmwgroup.harvard.edu/contact.html