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.

A Selective Etching Solution for Use with Patterned Self-Assembled Monolayers of Alkanethiolates on Gold

Abstract: Nl icrocontact pr int ing t r rCPtr is a technique that generates patterned self-assembled monolayers lSAtr{s t2 of' alkanethiolates t typically, hexadecanethiolate ) on the surfaces of goid,1 silver,l l and copper,l and of alkylsiloxanes on hydroxyl-terminated surf'aces.r' Patterned SAI{s of alkanethiolates serve as nanomc.ter-thick resists in certain etching solutions: the one we i.rave. used most extensively when gold is the underiving substrate has been aqueous KCN so lu t ion (p l l ' . 1 t . ICN ] . . ,0 .1 M) saturated with 0z.6 Llsing this etchant. t l-re patterns in the SAMs can be transf'erred faithfuih' into the thin fi lms of gold; the resulting patterns of gold can be used subsequently as secondarv masks for the etching (isotropic or anisotropic ) of' underlving la.vers of sil icon dioxide and si l icon; ' or i ls funct ional e lements ( for example, for microerlectrodese and diffraction gratingsi0). Microcontact printing is renrarkablv convenient fbr the fabrication of structures rvith feature sizes of 1 zrm and larger: it can be r-rsed. rvith more diff iculty and less reliabil itv. to fabricate f 'eatures with sizes down to 100

Electrostatic self-assembly of macroscopic crystals using contact electrification

Abstract: Self-assembly of components larger than molecules into ordered arrays is an efficient way of preparing microstructured materials with interesting mechanical and optical properties. Although crystallization of identical particles or particles of different sizes or shapes can be readily achieved, the repertoire of methods to assemble binary lattices of particles of the same sizes but with different properties is very limited. This paper describes electrostatic self-assembly of two types of macroscopic components of identical dimensions using interactions that are generated by contact electrification. The systems we have examined comprise two kinds of objects (usually spheres) made of different polymeric materials that charge with opposite electrical polarities when agitated on flat, metallic surfaces. The interplay of repulsive interactions between like-charged objects and attractive interactions between unlike-charged ones results in the self-assembly of these objects into highly ordered, closed arrays. Remarkably, some of the assemblies that form are not electroneutral-that is, they possess a net charge. We suggest that the stability of these unusual structures can be explained by accounting for the interactions between electric dipoles that the particles in the aggregates induce in their neighbours.

Electrical Breakdown of Aliphatic and Aromatic Self-Assembled Monolayers Used as Nanometer-Thick Organic Dielectrics

Abstract: This paper describes a new type of metal−insulator−metal junction based on self-assembled monolayers (SAMs). The junction consists of a drop of liquid mercury supporting a SAM, in contact with a flat metal surface (M‘), also supporting a SAM: that is, a Hg−SAM/SAM−M‘ junction. This junction is stable, easy to assemble, and reproducible: it can generate areas of contact down to 0.01 mm2 without photolithography. These properties suggest this junction as a useful “test bed” for experiments in molecular electronics. The junction allowed measurements of electrical properties of SAMs on different metals: M‘ = Ag, Au, Cu, and Hg. The work described here focused on the electrical breakdown voltage (BDV, the maximum voltage sustained by the junction). The BDV depends on M‘ (BDVAg = 3.2 ± 0.5 V; BDVHg = 3.1 ± 0.4 V; BDVCu = 3.0 ± 0.3 V; BDVAu = 1.5 ± 0.2 V for SAMs formed from hexadecanethiol) and correlates with the organizational parameters of the SAM on M‘: it increases as the packing density increases and ...

Polyacrylamides bearing pendant .alpha.-sialoside groups strongly inhibit agglutination of erythrocytes by influenza virus

Abstract: The initial step of invasion of a mammalian cell bv influenza virus is the binding of the viral membrane protein hernagglutinin (HA) to sialic acid (SA) residues of cell surface glvcoproteins and glycolipids,2 Tight-binding inhibitors of this associarion are potential inhibitors of infl uenza infection. Systematic examinations of monomeric derivatives of sialic acids have not, to date, revealed compounds binding significantly more tightlv to HA than rr-gl1-cosides of sialic acid.3'a A!though the binding of llA to a-sialosides is weak (K,.-t x l0-l M),3 the binding of influenza virus to celis appears to be strong. The qualitative difference between the strength of interaction between monomeric HA and rnethyl a-sialoside, and that. between virus and cell surface, probably reflecrs thc poly-valency of the latter interaction.s This inference is supported by the observation that certain glycoproteins. especiallv ,i,-macroglobulins. having high contents of sialic acrd itre stic,nF inhibitors of virus-induced agglutination of er',,throcytes.6'j Oi the known sialic acid containing givcoproteins^ onil' a ferv rrre capable of protecting ervthrocytcs from viral agglutination. and it is difficult to pinpoint the origin of this activirl. \\'c belicvc that the number and accessibility of sialic acid groups in these glvcoproteins play kev roles. The structures of these cornplex. naturalil' rrccurring. pxrlvvaieni hemagglutination inhibitors rre l;irgel-r' unknown. and ir ,' int-practical to prepare close analogues of thern by s lhesi\. ()r to study relations between their structure and strength of inhibrtrrtir. We therefore sought practical routes to synthetic macromolecule:; to which sialic acid groups could be attached, and in rvhich composition and strucxiure could be varied readily. Here we reflort that such substances can be prepared conveniently by' free-radical copolymerization of l, an acrvlamide derivative of sialic acid, *ith acrylamide and its de rivatives (Scheme l). T'he rnost activc of these copolynrers are powerful inhibitors of'hemagglurinttion bl' influenza virus.8 Polymerizations followed standard procedures.e We have not characterizcd these polymers full1,, but dialysis of representative (l) This research is part of a collaboration with (7) The inhibitory potency of some of these proteins has been increased by factors up to 600 by cross-linking them to form oligomeric protein clusters.

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.