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.

Carbonic Anhydrase-Inhibitor Binding: From Solution to the Gas Phase

Abstract: In this report, we compare the kinetic stabilities of noncovalent complexes between bovine carbonic anhydrase II(BCAII, EC 4.2.1.1) and para-substituted benzenesulfonamide inhibitors in the gas phase and in solution. These BCAII-inhibitor systems are attractive model systems due to the stability of carbonic anhydrase (CA) and its well characterized structure and ligand complexes, providing a basis for inferences regarding the protein structure in the gas phase and its ligand interactions. CA is a roughly spherical Zn(II) metalloenzyme having a conical binding pocket which catalyzes the hydration of CO{sub 2} to bicarbonate. A large body of data correlate structures of sulfonamide ligands with their binding constants to CA. A set of eight inhibitors was selected for this study, covering a wide range of binding affinities and varying in the length of their tails and aromatic content. The results demonstrate that relative stabilities of BCAII-inhibitor complexes differ substantially between the gas and liquid phases and also show the dominant role of polar surface interactions in the gas phase. 12 refs., 1 fig., 1 tab.

Integrated fluorescent light source for optofluidic applications

Abstract: This letter describes a simple fluidic light source for use “on-chip” in integrated microsystems. It demonstrates the feasibility of light sources based on liquid-core, liquid-cladding (L2) microchannel waveguides, with liquid cores containing fluorescent dyes. These fluorescent light sources, using both miscible and two-phase systems, are tunable in terms of the beam size, intensity and spectral content. The observed output intensity from fluorescent L2 light sources is comparable to standard fiber optic spectrophotometer light sources. Integration of fluorescent light sources during device fabrication removes both the need for insertion and alignment of conventional, optical-fiber light sources and the constraints on channel size imposed by fiber optics, albeit at the cost of establishing a microfluidic infrastructure.

Fabrication of two-dimensional arrays of microlenses and their applications in photolithography

Abstract: This paper describes several methods for the fabrication of microlenses, and demonstrates a lithographic technique that uses a microlens array to pattern the intensity of light incident on photoresist. Three different methods were used to fabricate microlenses: (i) self-assembly of transparent microspheres, (ii) melting and reflow of photoresist on glass substrates and (iii) self-assembly of liquid polymers on functionalized surfaces. These methods provide different advantages and convenience for the fabrication of microlenses. Microlens arrays produced by these techniques were used in photolithography to produce arrays of micropatterns in photoresist. The distribution of these micropatterns replicates the distribution of the microlenses in the array. Two types of illumination are used for exposure in this technique: collimated flood illumination and illumination through a mask. Depending on which type of exposure is used, a single microlens array can produce different patterns on its image plane: (i) an array of circular or noncircular microlenses under collimated illumination produces an array of optical micropatterns on an image plane positioned within micrometer distances from the lens array. The array of optical micropatterns corresponds to the distribution of spatial irradiance generated by simple lensing of the microlens array. The shapes of these micropatterns depend on the shapes and profiles of the microlenses. (ii) Under illumination patterned by a mask, each microlens approximately replicates the image of the patterned light source and produces a micro-scale image of this source on its image plane. The array of microlenses generates an array of repetitive micropatterns on the common image plane of the lens array. The shapes of the micropatterns depend on the patterns of the masks. Gray-scale masks can be used to produce repetitive microstructures with controlled profiles. Both techniques can generate microstructures with submicron resolution. We demonstrate that both methods produce arrays of uniform micropatterns over an area larger than 10 cm2.

Using bifunctional polymers presenting vancomycin and fluorescein groups to direct anti-fluorescein antibodies to self-assembled monolayers presenting d-alanine-d-alanine groups.

Abstract: This paper describes the synthesis of bifunctional polyacrylamides containing pendant vancomycin (Van) and fluorescein groups, and the use of these polymers to direct antibodies against fluorescein to self-assembled monolayers (SAMs) presenting d-alanine-d-alanine (dAdA) groups. These polymers bind biospecifically to these SAMs via interactions between the dAdA and Van groups and serve as a molecular bridge between the anti-fluorescein antibodies and the SAM. The binding events were characterized using surface plasmon resonance spectroscopy and fluorescence microscopy. The paper demonstrates that polyvalent, biospecific, noncovalent interactions between a polymer and a surface can be used to tailor the properties of the surface in molecular recognition. It also represents a first step toward the design of polymers that direct arbitrarily chosen antibodies to the surfaces of cells.

Use of Electroless Silver as the Substrate in Microcontact Printing of Alkanethiols and Its Application in Microfabrication

Abstract: We have employed electroless deposition to prepare smooth films (mirrors) of silver that could be used as substrates in microcontact printing (μCP) of alkanethiols. Good-quality SAMs of hexadecanethiolate were formed on thin films of electroless silver by printing with an elastomeric stamp; these SAMs were effective resists in protecting the underlying silver from etching in an aqueous ferricyanide solution. Thin films of silver prepared by electroless deposition show a granular morphology (the grain sizes are ∼30−60 nm) and have a rougher surface than those prepared using e-beam or thermal evaporation. As a result, hexadecanethiol liquid spreads more rapidly on electroless silver than on evaporated silver when μCP is carried out in air. This process of reactive spreading limits the resolution and fidelity of pattern transfer to electroless silver films by μCP, but could also be used as a convenient method for reducing the sizes of features of SAMs generated using μCP. The smallest features that we have f...

I and i

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 …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

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。

The Theory of Island Biogeography

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

Large-scale pattern growth of graphene films for stretchable transparent electrodes

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.

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

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.