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 …

I and i

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。

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

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. Our device layout features local gates that provide excellent capacitive coupling between the gate and nanotube, enabling strong electrostatic doping of the nanotube from p-doping to n-doping and the study of the nonconventional long-range screening of charge along the one-dimensional nanotubes. The transistors show favorable device characteristics such as high gain (>10), a large on-off ratio (>10(5)), and room-temperature operation. Importantly, the local-gate layout allows for integration of multiple devices on a single chip. Indeed, we demonstrate one-, two-, and three-transistor circuits that exhibit a range of digital logic operations, such as an inverter, a logic NOR, a static random-access memory cell, and an ac ring oscillator.

/pdf/logic-circuits-with-carbon-nanotube-transistors-vw5igdkjzb.pdf

Logic circuits with carbon nanotube transistors

3.6.1. Polishing and Cleaning 2663 3.6.2. Vacuum and Heat Treatments 2664 3.6.3. Carbon Electrode Activation 2665 3.7. Summary and Generalizations 2666 4. Advanced Carbon Electrode Materials 2666 4.1. Microfabricated Carbon Thin Films 2666 4.2. Boron-Doped Diamond for Electrochemistry 2668 4.3. Fibers and Nanotubes 2669 4.4. Carbon Composite Electrodes 2674 5. Carbon Surface Modification 2675 5.1. Diazonium Ion Reduction 2675 5.2. Thermal and Photochemical Modifications 2679 5.3. Amine and Carboxylate Oxidation 2680 5.4. Modification by “Click” Chemistry 2681 6. Synopsis and Outlook 2681 7. Acknowledgments 2682 8. References 2682

/pdf/advanced-carbon-electrode-materials-for-molecular-2y6b22van0.pdf

Advanced carbon electrode materials for molecular electrochemistry.

Among the variety of roles for nanopores in biology, an important one is enabling polymer transport, for example in gene transfer between bacteria1 and transport of RNA through the nuclear membrane2. Recently, this has inspired the use of protein3,4,5 and solid-state6,7,8,9,10 nanopores as single-molecule sensors for the detection and structural analysis of DNA and RNA by voltage-driven translocation. The magnitude of the force involved is of fundamental importance in understanding and exploiting this translocation mechanism, yet so far it has remained unknown. Here, we demonstrate the first measurements of the force on a single DNA molecule in a solid-state nanopore by combining optical tweezers11 with ionic-current detection. The opposing force exerted by the optical tweezers can be used to slow down and even arrest the translocation of the DNA molecules. We obtain a value of 0.24±0.02 pN mV−1 for the force on a single DNA molecule, independent of salt concentration from 0.02 to 1 M KCl. This force corresponds to an effective charge of 0.50±0.05 electrons per base pair equivalent to a 75% reduction of the bare DNA charge.

/pdf/direct-force-measurements-on-dna-in-a-solid-state-nanopore-5awxkb4yef.pdf

Direct force measurements on DNA in a solid-state nanopore

Carbon nanotube transistors have outstanding potential for electronic detection of biomolecules in solution The physical mechanism underlying sensing however remains controversial, which hampers full exploitation of these promising nanosensors Previously suggested mechanisms are electrostatic gating, changes in gate coupling, carrier mobility changes, and Schottky barrier effects We argue that each mechanism has its characteristic effect on the liquid gate potential dependence of the device conductance By studying both the electron and hole conduction, the sensing mechanisms can be unambiguously identified From extensive protein-adsorption experiments on such devices, we find that electrostatic gating and Schottky barrier effects are the two relevant mechanisms, with electrostatic gating being most reproducible If the contact region is passivated, sensing is shown to be dominated by electrostatic gating, which demonstrates that the sensitive part of a nanotube transistor is not limited to the contact region, as previously suggested Such a layout provides a reliable platform for biosensing with nanotubes

Identifying the mechanism of biosensing with carbon nanotube transistors

Noble metal nanoparticles can be electrodeposited on carbon nanotubes under potential control. The nanotube sidewalls serve both as the electrodeposition template and as the wire electrically connecting the deposited nanoparticles.

Electrodeposition of Noble Metal Nanoparticles on Carbon Nanotubes

When a single strand of DNA is threaded through a nanopore, a direct test of the effect of pore size indicates that a hydrodynamic model for the process should include the coupled Poisson–Boltzmann and Stokes equations. Despite gel electrophoresis being one of the main workhorses of molecular biology, the physics of polyelectrolyte electrophoresis in a strongly confined environment remains poorly understood. Theory indicates that forces in electrophoresis result from interplay between ionic screening and hydrodynamics1,2, but these ideas could so far be addressed only indirectly by experiments based on macroscopic porous gels. Here, we provide a first direct experimental test by measuring the electrophoretic force on a single DNA molecule threading through a solid-state nanopore3 as a function of pore size. The stall force gradually decreases on increasing the nanopore diameter from 6 to 90 nm, inconsistent with expectations from simple electrostatics and strikingly demonstrating the influence of the hydrodynamic environment. We model this process by applying the coupled Poisson–Boltzmann and Stokes equations in the nanopore geometry4,5 and find good agreement with the experimental results.

/pdf/origin-of-the-electrophoretic-force-on-dna-in-solid-state-o85b8vrjiw.pdf

Origin of the electrophoretic force on DNA in solid-state nanopores

The interplay between discrete vibrational and electronic degrees of freedom directly influences the chemical and physical properties of molecular systems. This coupling is typically studied through optical methods such as fluorescence, absorption and Raman spectroscopy. Molecular electronic devices provide new opportunities for exploring vibration-electronic interactions at the single molecule level. For example, electrons injected from a scanning tunnelling microscope tip into a metal can excite vibrational excitations of a molecule situated in the gap between tip and metal. Here we show how current directly injected into a freely suspended individual single-wall carbon nanotube can be used to excite, detect and control a specific vibrational mode of the molecule. Electrons tunnelling inelastically into the nanotube cause a non-equilibrium occupation of the radial breathing mode, leading to both stimulated emission and absorption of phonons by successive electron tunnelling events. We exploit this effect to measure a phonon lifetime of the order of 10 ns, corresponding to a quality factor of well over 10,000 for this nanomechanical oscillator.

Serge G. Lemay

Papers

Direct force measurements on DNA in a solid-state nanopore

Identifying the mechanism of biosensing with carbon nanotube transistors

Electrodeposition of Noble Metal Nanoparticles on Carbon Nanotubes

Origin of the electrophoretic force on DNA in solid-state nanopores

Electrical generation and absorption of phonons in carbon nanotubes