George M. Whitesides

Bio: George M. Whitesides is an academic researcher from Harvard University. The author has contributed to research in topics: Monolayer & 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.

Templated Self‐Assembly: Formation of Folded Structures by Relaxation of Pre‐stressed, Planar Tapes

Abstract: germanium nanowires grow at an inclined angle on a non-ger-manium (111) substrate due to crystallographic mismatch. We demonstrate the feasibility of controlled synthesis of individual vertical semiconducting germanium nanowires. These nano-wires can be directly integrated into fabricated devices [1,2] to produce nanoscale vertical transistors. Other applications for individual vertical germanium nanowires or arrays of high-density germanium nanowires include terapixel infrared photodetection systems, memory devices with metal oxide/ semiconductor structures and germanium nanowires, germa-nium-based cryogenic power electronics for deep-space exploration , and monolithic germanium nanoresonators. Large-scale synthesis of functionalized germanium nanostructures may find chemotherapeutic applications in nanomedicine, as certain germanium compounds exhibit low mammalian toxicity but marked activity against certain bacteria. Other applications may include high-sensitivity functionalized biosensors or catalysts for nanoelectroplating. Germanium oxide is a photo-luminescent material with peak energies at 3.1 eV and 2.2 eV. Oxidation of the germanium nanowires can produce germa-nium oxide nanowires for photoluminescence studies and optoelectronic applications. Experimental Doped and intrinsic germanium(III) substrates were coated with poly(methyl methacrylate) (PMMA, 950 kg mol ±1 relative molecular mass, 2 wt.-% in chlorobenzene, spin-coated at 5000 rpm and 200 C, with a post-bake), exposed with an electron beam (Hitachi H-700, 600±700 lC cm ±2 , 30 kV), and developed with methyl isobutyl ketone/ isopropanol (1:3 v/v, 30 s, 23 C, 20±30 s isopropanol rinse). Gold (99.95 % metal basis) was deposited by ion-beam sputtering technology , and the resist lift-off process was performed in acetone (1±2 min, sonication, 23 C). The germanium nanowires were synthesized using the gold catalyst mediated homoepitaxial growth approach in a dual-zone tubular reaction chamber setup. The source, composed of a 1:1 weight ratio of germanium powder (Alfa Aesar, 99.999 % metal basis) and synthetic graphite powder (Alfa Aesar, 99.9995 % metal basis), was placed upstream of the substrate. The graphite additive provides enhanced surface area for the evaporation of germanium at elevated temperature and control of the germanium partial pressure at a given carrier gas flow rate and fixed source temperature. Graphite also reduces the amount of germanium oxide (native oxide on the as-purchased ger-manium powder) by carbothermal reduction. Thermodynamic considerations [3] suggest that formation of crystalline germanium carbide nanowires is highly unlikely due to the disproportionate heats of formation of gaseous carbon and germanium species, the intrinsic metastability of the Ge±C bond compared with C±C bonds, and the thermodynamic insolubility of carbon in crystalline germanium at a wide range of temperatures and …

Using ion channel-forming peptides to quantify protein-ligand interactions.

Abstract: This paper proposes a method for sensing affinity interactions by triggering disruption of self-assembly of ion channel-forming peptides in planar lipid bilayers. It shows that the binding of a derivative of alamethicin carrying a covalently attached sulfonamide ligand to carbonic anhydrase II (CA II) resulted in the inhibition of ion channel conductance through the bilayer. We propose that the binding of the bulky CA II protein (MW approximately 30 kD) to the ion channel-forming peptides (MW approximately 2.5 kD) either reduced the tendency of these peptides to self-assemble into a pore or extracted them from the bilayer altogether. In both outcomes, the interactions between the protein and the ligand lead to a disruption of self-assembled pores. Addition of a competitive inhibitor, 4-carboxybenzenesulfonamide, to the solution released CA II from the alamethicin-sulfonamide conjugate and restored the current flow across the bilayer by allowing reassembly of the ion channels in the bilayer. Time-averaged recordings of the current over discrete time intervals made it possible to quantify this monovalent ligand binding interaction. This method gave a dissociation constant of approximately 2 microM for the binding of CA II to alamethicin-sulfonamide in the bilayer recording chamber: this value is consistent with a value obtained independently with CA II and a related sulfonamide derivative by isothermal titration calorimetry.

Electrical Textile Valves for Paper Microfluidics

Abstract: This paper describes electrically-activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept can be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100-1000 V) between the textile and the liquid, the valve opens and the liquid penetrates the textile. These valves actuate in less than 1 s, require low energy (≈27 µJ per actuation), and work with a variety of aqueous solutions, including those with low surface tension and those containing bioanalytes. They are bistable in function, and are, in a sense, the electrofluidic analog of thyristors. They can be integrated into paper microfluidic devices to make circuits that are capable of controlling liquid, including autonomous fluidic timers and fluidic logic.

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.