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George M. Whitesides

Bio: George M. Whitesides is an academic researcher from Harvard University. The author has contributed to research in topics: Microcontact printing & Self-assembled monolayer. The author has an hindex of 240, co-authored 1739 publications receiving 269833 citations. Previous affiliations of George M. Whitesides include University of California, Davis & University of Texas at Austin.


Papers
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Journal ArticleDOI
01 Oct 2007-Small
TL;DR: The use of microfluidic technology, with closely coupled flow-focusing units, guarantees that the emulsions are mixed locally at a controlled local stoichiometry, to form a wide variety of highly organized periodic lattices.
Abstract: A method is described for the formation of stable, composite aqueous emulsions of 1) combinations of distinct families of bubbles of nitrogen, 2) combinations of distinct families of droplets of an organic fluid (either perfluoro(methyl)decalin or hexadecane), and 3) combinations of bubbles and droplets. A system of two or three microfluidic flow-focusing units is coupled to a single outlet channel. The composite emulsions can be precisely tuned, both in their composition and in the number fraction of components--either bubbles or droplets--of different types. The use of microfluidic technology, with closely coupled flow-focusing units, guarantees that the emulsions are mixed locally at a controlled local stoichiometry. The emulsions self-assemble in a nonequilibrium process to form a wide variety of highly organized periodic lattices.

85 citations

Journal ArticleDOI
TL;DR: In this article, microcontact printing was used to form nanometer scale patterns of self-assembled monolayers (SAMs) on amorphous Si, crystalline Si, and SiO2 using octadecyltrichlorosilane (OTS) as the ink and an elastomer as the stamp.
Abstract: Microcontact printing was used to form nanometer scale patterns of self-assembled monolayers (SAMs) on amorphous Si, crystalline Si, and SiO2 using octadecyltrichlorosilane (OTS) as the ink and an elastomer as the stamp. The patterns were subsequently transferred into crystalline Si substrates or amorphous Si films using the SAM of OTS as the resist film. Atomic force microscopy was used to characterize the quality of the SAM and the resulting patterns. Using a Si pillar structure as the master, “pancakes” of less than 80 nm in size were formed by over etching of the patterned OTS film on amorphous Si using KOH. The size of the resulting amorphous Si pancakes can be controlled by the etching time.

85 citations

Journal ArticleDOI
TL;DR: These findings expand the range of interactions previously thought to occur between ions and proteins by suggesting that (i) weakly hydrated anions can bind complementarily shaped hydrophobic declivities, and (ii) ion-induced rearrangements of water within protein concavities can extend well beyond the first hydration shells of the ions that trigger them.
Abstract: This paper uses the binding pocket of human carbonic anhydrase II (HCAII, EC 4.2.1.1) as a tool to examine the properties of Hofmeister anions that determine (i) where, and how strongly, they associate with concavities on the surfaces of proteins and (ii) how, upon binding, they alter the structure of water within those concavities. Results from X-ray crystallography and isothermal titration calorimetry show that most anions associate with the binding pocket of HCAII by forming inner-sphere ion pairs with the Zn2+ cofactor. In these ion pairs, the free energy of anion–Zn2+ association is inversely proportional to the free energetic cost of anion dehydration; this relationship is consistent with the mechanism of ion pair formation suggested by the “law of matching water affinities”. Iodide and bromide anions also associate with a hydrophobic declivity in the wall of the binding pocket. Molecular dynamics simulations suggest that anions, upon associating with Zn2+, trigger rearrangements of water that exten...

84 citations

Journal ArticleDOI
TL;DR: Bioinspired research has the potential to be accessible to laboratories that have limited resources, to offer routes to new and useful function, and to bridge differences in technical and cultural interactions of different geographical regions.
Abstract: ‘Bioinspiration’—using phenomena in biology to stimulate research in non-biological science and technology—is a strategy that suggests new areas for research. Beyond its potential to nucleate new ideas, bioinspiration has two other interesting characteristics. It can suggest subjects in research that are relatively simple technically; it can also lead to areas in which results can lead to useful function more directly than some of the more familiar areas now fashionable in chemistry. Bioinspired research thus has the potential to be accessible to laboratories that have limited resources, to offer routes to new and useful function, and to bridge differences in technical and cultural interactions of different geographical regions.

84 citations

Journal ArticleDOI
TL;DR: In this article, a method of fabricating microstruc-tures of glassy carbon and other high-carbon solids is described, which uses micromolding of polymers to form precursors to these structures, and pyrolysis of these polymeric micro-structures to form the carbon solids.
Abstract: Communications formed with this method is limited by the resolution of the microcontact printing (-0.2 pm)J2] by the ability to set the angle and position of the stamp relative to the object to be patterned (-0.01\", and-2 Fm for our apparatus))'] and by uncertainties in the dimensions of the curved support. The composition of these parts is limited to materials that can be electrodeposited. We believe that our method offers a simple means for fabrication of complex three-dimensional microstructures that will be a valuable complement to other means for microfabrication. Many applications in biotechnology and MEMS should be found. This paper describes a method of fabricating microstruc-tures of glassy carbon and other high-carbon solids. This method uses micromolding of polymers to form precursors to these structures, and pyrolysis of these polymeric micro-structures to form the carbon solids. These microstructures are stiff and can be either electrically insulating or conducting , depending on their thermal history. In addition, carbon structures can be very stable thermally, and the surface of carbon is readily functionalized.[',21 We are developing carbon microstructures as components in microelectromecha-nical systems (MEMS), microreactors, and other systems in which thermal stability, chemical inertness, engineered surface properties, and electrical conductivity are useful characteristics. The mechanical, electrical, and chemical properties of high-carbon solids can be controlled over wide ranges by the temperature at which these solids are prepared.'1231 The range of electrical properties that can be achieved is especially interesting: the conductivity of a phenol-formalde-hyde resin can be controlled over a range of-10L9!x' cm-' by pyrolysis. Insulating, semiconducting, and semimetallic behaviors have been observed for pyrolyzed novolac photoresists, depending on the pyrolysis conditions.[42s1 Glassy carbon is often produced by carbonization of organic polymeric precursors; resins of furfuryl alcohol, phenol -formaldehyde, acetone-furfural, or furfuryl alcohol-phenol copolymers are among those commonly used for this purpose.'*] In this work, copolymers of phenol-formal-dehyde or furfuryl alcohol-phenol were formed in patterns on appropriate substrates (silica, Si/Si02, glassy carbon) using micro-molding in capillaries (MIMIC)[6-s1 and micro-transfer molding (pTM).I9' The resulting polymeric structures were carbonized at high temperatures in vacuum (600-1100 \"C, 10-6-10-7 torr) or in an inert atmosphere (ar-gon), either on the substrate or after being lifted from the surface, to yield high-carbon structures having micron-scale dimensions. Supported structures of a phenol-formaldehyde resin and of a furfuryl alcohol-modified phenolic resin were prepared by MIMIC, using a patterned poly(dimethylsi1oxane)

83 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

14,171 citations

Journal ArticleDOI
05 Feb 2009-Nature
TL;DR: The direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers is reported, and two different methods of patterning the films and transferring them to arbitrary substrates are presented, implying that the quality of graphene grown by chemical vapours is as high as mechanically cleaved graphene.
Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

10,033 citations

Journal ArticleDOI
29 Aug 1997-Science
TL;DR: In this article, a general approach for multilayers by consecutive adsorption of polyanions and polycations has been proposed and has been extended to other materials such as proteins or colloids.
Abstract: Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.

9,593 citations