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.

Self-assembled monolayer directed patterning of surfaces

Abstract: A technique for creating patterns of material deposited on a surface involves forming a self-assembled monolayer in a pattern on the surface and depositing, via chemical vapor deposition or via sol-gel processing, a material on the surface in a pattern complementary to the self-assembled monolayer pattern. The material can be a metal, metal oxide, or the like. The surface can be contoured, including trenches or holes, the trenches or holes remaining free of self-assembled monolayer while the remainder of the surface is coated. When exposed to deposition conditions, metal or metal oxide is deposited in the trenches or holes, and remaining portions of the article surface remain free of deposition. The technique finds particular use in creation of conductive metal pathways selectively within holes passing from one side of a substrate to another.

Molecular Rectification in Metal−SAM−Metal Oxide−Metal Junctions

Abstract: This Article compares the ability of self-assembled monolayers (SAMs) of alkanethiolates with ferrocene (Fc) head groups (SC11Fc), and SAMs of alkanethiolates lacking the Fc moiety (SC10CH3 and SC14CH3), to conduct charge. Ultraflat surfaces of template-stripped silver (AgTS) supported these SAMs, and a eutectic alloy of gallium and indium (EGaIn), covered with a skin of gallium oxide (presumably Ga2O3), formed electrical top-contacts with them. EGaIn is a liquid at room temperature, but its spontaneously formed surface oxide skin gives it apparent non-Newtonian properties and allows it to be molded into conically shaped tips; these tips formed soft electrical contacts with SAMs and formed stable SAM-based tunneling junctions in high (70−90%) yields. Measurements of current density, J, versus applied voltage, V, showed that tunneling junctions composed of SAMs of SC11Fc rectify current with a rectification ratio R ≈ 1.0 × 102 (R = |J(−V)|/|J(V)| at ±1 V and with a log-standard deviation of 3.0). In contra...

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Abstract: : Oxidation of polyethylene with chromic acid/sulfuric acid generates a material (PE-CO2H) having a high density of carboxylic acid and ketone functionalities in a thin surface layer on the polymer. This paper determines the extent of ionization of the surface and near-surface carboxylic acid groups of these materials in contact with water as a function of pH using three experimental techniques: measurement of attenuated total reflectance infrared (ATR-IR) spectra, measurement of contact angles, and direct potentiometric titration. On the basis of correlations between results obtained using these three techniques, we propose an equation relating the contact angles an aqueous solution having a given value of pH and the extent of ionization (a subscript i) of those carboxylic acid groups that are directly exposed to the solution. These carboxylic acid groups have broad titration curves, and have CO2H groups that are less acidic than soluble carboxylic acids. The initial ionization of these carboxylic acid groups occurs when the solution is approximately pH = 6. The detailed structures of these oxidized polymer surface layers and the nature of the interactions between the carboxylic acid and carboxylate ions in them are still not completely defined. Salt effects on the extent of ionization a subscript i at a particular value of pH are unexpectedly small, and suggest that charge-charge interactions between carboxylate ions may not dominate the titration curves. This work demonstrates the usefulness of contact angle in following chemical changes occurring in organic functional groups of surfaces.

Microsolidics: Fabrication of Three‐Dimensional Metallic Microstructures in Poly(dimethylsiloxane)

Abstract: This Communication describes a method of fabricating complex metallic microstructures in 3D by injecting liquid solder into microfluidic channels, and allowing the solder to cool and solidify; after fabrication, the metallic structures can be flexed, bent, or twisted This method of fabrication—which we call microsolidics—takes advantage of the techniques that were developed for fabricating microfluidic channels in poly(dimethylsiloxane) (PDMS) in 2D and 3D, uses surface chemistry to control the interfacial free energy of the metal– PDMS interface, and uses techniques based on microfluidics, but ultimately generates solid metal structures This approach makes it possible to build flexible electronic circuits or connections between circuits, complex embedded or freestanding 3D metal microstructures, 3D electronic components, and hybrid electronic–microfluidic devices There are several techniques for making metal microstructures in 3D Electroplating and electroless deposition are routinely used to construct microstructures with metallic layers several nanometers to several microns thick in 2D or 3D [1–11] To generate solid replicas of 3D objects, several groups have developed a technique, referred to as “microcasting”, to form metals in order to fabricate microparts (eg, posts and gears) with features as small as 10 lm and aspect ratios as high as 10 from steel, zirconia, and alumina [12,13] Techniques based on LIGA (Lithographie, Galvanoformung, und Abformung) produce even more complicated metallic objects by depositing a metal onto a molded polymer template that is subsequently removed to yield an open structure (such as a honeycomb arrangement of cells) [14,15] In principle, these approaches can be used to pattern metals of any thickness to produce features with an aspect ratio that is larger than that produced using electroplating

Selective Deposition of Proteins and Cells in Arrays of Microwells

Abstract: This paper describes a method for depositing proteins and cells selectively into microwells fabricated in poly(dimethylsiloxane)an elastomeric organic polymer. The arrays of microwells were generated using soft lithography. The surface between the wells was coated with bovine serum albumin, and the surface within the wells was coated with fibronectin (FN)an adhesive extracellular matrix protein. Fluorescence staining of FN using antibodies indicated that the protein had adsorbed to the wells selectively. Exposure of the FN-coated wells to a suspension of bovine capillary endothelial cells resulted in attachment and spreading of the cells only in the wells. This method for patterning cells was demonstrated with wells of several diameters (≤100 μm) and depths (≤50 μm). It should be useful for (i) the development of sensors based on arrays of cells, (ii) screening combinatorial libraries of ligands on cells, and (iii) testing the effect on cells of compounds and samples relevant to problems in environmental ...

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.