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.

Emulsification in a microfluidic flow-focusing device: effect of the viscosities of the liquids

Abstract: We report the results of a comparative study of microfluidic emulsification of liquids with different viscosities. Depending on the properties of the fluids and their rates of flow, emulsification occurred in the dripping and jetting regimes. We studied the characteristic features and typical dependence of the size and of the size distribution of droplets in each regime. For each liquid, we identified a range of hydrodynamic conditions promoting generation of highly monodisperse droplets. Viscosity played an important role in emulsification: highly viscous liquids were emulsified into larger droplets with lower polydispersity. Although it was not possible to provide a unified scaling for the volumes of the droplets, our results suggest that the break-up dynamics of the lower viscosity fluids resembles the rate-of-flow-controlled break-up, as reported earlier for the formation of bubbles in flow-focusing geometries [Garstecki P, Stone HA, Whitesides GM (2005) Phys Rev Lett 94:164501]. The results of this study can be helpful for a rationalized selection of liquids for the controlled formation of droplets with a predetermined size and with a narrow distribution of sizes.

Polyacrylamides Bearing Pendant α-Sialoside Groups Strongly Inhibit Agglutination of Erythrocytes by Influenza Virus: The Strong Inhibition Reflects Enhanced Binding through Cooperative Polyvalent Interactions

Abstract: An ELISA assay is described for measuring the binding of influenza virus A-X31 to α-sialoside groups that are linked to biotin-labeled polyacrylamides. The efficacy of these polymers in inhibiting the adhesion of influenza virus to erythrocytes (as measured by a hemagglutination assay) was shown to be directly related to the binding affinity of the polymers for the viral surface: the differences in inhibitory efficacy among the polymeric inhibitors and monomeric α-methyl sialoside, among fractions of a polymeric, polyvalent inhibitor with narrow molecular weight ranges, and among polymeric inhibitors prepared by copolymerization or modification of a preformed polymer chain, all correlated with differences in the affinity of the inhibitors for the surface of the virus. The polymeric inhibitors studied had affinities for the viral surface that ranged between 103 and >106 greater than α-methyl sialoside, on the basis of total sialic acid groups in solution. The role of steric stabilization in the mechanism ...

X-Ray Specular Reflection Studies of Silicon Coated by Organic Monolayers (Alkylsiloxanes)

Abstract: X-ray specular reflectivity has been used to characterize the structure of silicon--silicon-oxide surfaces coated with chemisorbed hydrocarbon monolayer films (alkylsiloxanes). Using synchrotron radiation the reflectivity was followed over 9 orders of magnitude, from grazing incidence to an incident angle of \ensuremath{\varphi}\ensuremath{\approxeq}6.5\ifmmode^\circ\else\textdegree\fi{}, or q=(4\ensuremath{\pi}/\ensuremath{\lambda})sin(\ensuremath{\varphi})=0.8 A${\r{}}^{\mathrm{\ensuremath{-}}1}$, allowing a spatial resolution of features approximately \ensuremath{\pi}/0.8\ensuremath{\approxeq}4.0 A\r{} along the surface normal. Analysis was performed by fitting the data to reflectivities calculated from models of the surface electron density and by calculating Patterson functions directly from the data. Although the measured reflectivities could be equally well described by different sets of model parameters, the electron densities calculated from these different parameters were remarkably alike. Inspection of the electron densities allowed identification of a layer of ${\mathrm{SiO}}_{2}$ (\ensuremath{\approxeq}17-A\r{} thick), a layer of head-group region where the alkylsiloxane adsorbs to the ${\mathrm{SiO}}_{2}$, and the hydrocarbon layer. Fitting the data also required that the various interfaces have different widths. The fact that the same local hydrocarbon density of 0.85 g/${\mathrm{cm}}^{3}$ was observed for both fully formed and partially formed monolayers with alkane chains of varying length excluded a model in which the partially formed monolayer was made up of separated islands of well-formed monolayers. Measurements before and after chemical reaction of a monolayer in which the alkyl chain was terminated by an olefinic group demonstrated the ability to use x-ray reflectivity to characterize chemical changes. The effects of radiation damage on these types of measurements are described.

An Integrated Approach to a Portable and Low‐Cost Immunoassay for Resource‐Poor Settings

Abstract: The development of technology for use in resource-poor countries encounters a specific type of challenge not ordinarily faced in academic science: the technology must be inexpensive and it must work with minimal infrastructure. This challenge is particularly severe when the problems being solved are, by their nature, ones that require high-technology solutions. For these kinds of problems, the elegance of the solutions must lie in the use of science to guide the assembly of readily available components into a simple, workable, and well-integrated package. In this paper, we describe an integrated approach to a miniaturized immunoassay called a “POCKET immunoassay” (“POCKET” is short for portable and cost-effective). This immunoassay has, we believe, the potential to be inexpensive and operable with minimal equipment and technical skills, and shows an analytical performance approaching that of enzyme-linked immunosorbent assays (ELISA) performed in a bench-top format in clinical laboratories. A top priority for improving health in developing countries is technology for simple, affordable diagnosis of infectious diseases. Immunoassays such as ELISA are the most reliable and widely used methods for detecting antigens and antibodies, but they require expensive and bulky instruments for optical detection, hours of incubation for diffusionlimited reactions on the surface, and many steps of pipetting. 3] These constraints prevent the use of ELISA in settings that require low-cost or compact equipment, and in environments that lack electricity or trained personnel. One application with these requirements is the detection of infectious diseases in the field in developing countries; 4,5] other potential uses include point-of-care diagnostics by first responders and in health clinics, and detection of biological warfare agents in the field. Immunochromatographic assays (also known as “strip tests” and “lateral-flow

Microfabrication through Electrostatic Self-Assembly

Abstract: We use electrostatic interactions to direct the patterning of gold disks having ∼10-μm diameters on functionalized surfaces. Planar and curved substrates with patterned surface charge were generated either by microcontact printing or by photolithography. Small charged gold disks were generated by electroplating gold into photoresist molds and derivatizing these disks with charged self-assembled monolayers. When agitated as a suspension in contact with the patterned surfaces, the charged gold disks deposited specifically but as disordered aggregates on regions presenting the opposite charge. Positively-charged disks deposited on phosphonate-, carboxylate-, and SiOH-terminated surfaces but not on trimethylammonium- and dimethylammonium-terminated surfaces, and vice versa for negatively-charged disks. Methyl- and CF3-terminated surfaces resisted deposition of disks of either charge. Selective and dense assembly was achieved in methanol, ethanol, 2-propanol, and dioxane; in water, deposition was nonspecific. ...

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.