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YINQE Seminars
Unless otherwise noted, all YINQE seminars meet on Fridays, 12:00-1:00 pm in the J. Robert Mann, Jr. Student Center, Dunham Lab 107.
 
Prof. Sigworth arrives at seminar Prof. Dufresne presents results
Spring 2009
April 24
Nano carbon: from molecular speedbumps to atomic drums
Paul L. McEuen,Professor, Laboratory of Atomic and Solid State Physics, Cornell University
Carbon takes many forms, from precious diamond to lowly graphite. Surprisingly, it is the latter form that is the most prized by nanoscientists. Graphene, a single layer of graphite, is the first atomically thin membrane. It is electrically conducting, mechanically strong, and chemically robust. Rolled up into a nanometer-diameter cylinder -- a carbon nanotube -- it becomes the nanoscientist’s version of a biological polymer, about the same dimensions as a strand of DNA but much stiffer and stronger. In this talk, I will present some of our group’s recent results on these carbon-based materials, concentrating on their mechanical and biological uses. Mechanical examples include the creation of the first graphene atomic drumhead and the world’s thinnest vacuum window. We will also fashion nanotubes into nanoguitars, use them as speedbumps for membrane-bound proteins, and explore their unique advantages as substrates for single-molecule optical tweezing experiments.
April 10
Aggregation and Bacterial Cytotoxicity of Carbon-Based Nanomaterials in Aquatic Environments
Menachem Elimelech, Roberto C. Goizueta Professor of Environmental and Chemical Engineering
With the emergence of nanotechnology, engineered nanomaterials, such as carbon nanotubes and fullerenes, will inevitably find their way into natural waters. Understanding the aggregation behavior of these nanomaterials is important for predicting their transport, reactivity, and bioavailability in aquatic environments. This presentation will focus on the aggregation behavior of carbon nanotubes and fullerene (C-60) nanoparticles. The early-stage aggregation kinetics of these nanomaterials are investigated via time-resolved dynamic light scattering under a range solution chemistries (monovalent and divalent cations, and presence of humic acid and macromolecules). The mechanisms of aggregation will be related to solution chemistry and the physicochemical properties of the nanomaterials. In addition to the aggregation kinetics, recent work on the interaction of carbon nanotubes with bacterial cells will be described and the environmental implications of carbon-based nanomaterial cytotoxicity will be discussed.
Demonstration of Quantum Algorithms with a Solid-State Device
Robert Schoelkopf, William A. Norton Professor of Applied Physics & Physics
By using the “spooky” aspects of quantum physics, such as entanglement and superposition, quantum computers are predicted to be vastly more powerful than their classical counterparts for certain tasks. While some technologies, such as NMR and trapped ions, have succeeded in making and manipulating a handful of quantum bits (qubits), they look quite different from a conventional computer, and there are many obstacles to building large-scale processors. I will describe recent experiments in our lab in which we demonstrate a rudimentary (two-qubit) quantum processor based on superconducting circuits. We show that we can perform both single and two-bit logic operations with relatively high fidelity, which can be combined to form simple algorithms. I will describe a two-qubit Grover’s search using this system, which shows many of the features necessary for quantum computation.
March 27
1+1>2: Electrostatic Forces Are Not Always Pair-wise Additive
Eric Dufresne, Professor, Department of Mechanical Engineering
We exploit optical forces and thermal fluctuations to measure femtoNewton scale forces between micron-sized plastic particles floating in oil. Particle surfaces spontaneously charge and we observe long-range electrostatic repulsions between pairs. Interestingly, the repulsion between any pair of particles can be strongly reduced when other particles are nearby. This effect is not accounted for by the usual suspects: nonlinearity in the Poisson-Boltzmann equation or counter-ion correlations. However, we can quantitatively predict interparticle forces in a variety of geometries by simply assuming that the surface charge densities adjust to keep the surface electrostatic potentials at a fixed value.
Single Crystals of Mesostructured Soft Materials
Chinedum Osuji, Assistant Professor, Department of Chemical Engineering
Self-assembled soft materials offer rich opportunities for the design of an impressive variety of functional systems, ranging from photonic crystals to high-density storage media, separations membranes and templates for inorganic synthesis, for example. In many cases, a critical limitation in their utilization is the inability to reliably and precisely exercise control over their tertiary level structure. In the vocabulary of traditional materials science, we lack good control of grain size and orientation. The ability to direct the self-assembly of soft materials such as colloidal crystals, block copolymer melts and lyotropic mesophases with high fidelity is thus critical to advancing their utility in areas identified above. High magnetic fields offer a promise as a flexible tool for the alignment of nanostructures in self-assembled soft materials. This approach relies on the presence of sufficient anisotropy of magnetic susceptibility via which an external field can be used to impart strong preferential alignment. The required anisotropy, essentially absent in amorphous organic materials, may be provided by the presence of liquid crystalline order in the system. Diamagnetic alignment of anisotropic systems, however, can often result in the production of degenerate arrangements in phases with uniaxial symmetry. This talk will discuss issues related to the problem of producing non-degenerate alignments of soft materials. I will demonstrate that judicious application of high magnetic fields can drive diamagnetic alignment of surfactant mesophases in both lamellar and hexagonal structure regimes, leading to very highly ordered systems.
February 27
Label-Free Sensing with Silicon Nanowires
Mark Reed, Professor, Department of Electrical Engineering
Nanoscale electronic devices have the potential to achieve exquisite sensitivity as sensors for the direct detection of molecular interactions, thereby decreasing diagnostics costs and enabling previously impossible sensing in disparate field environments. Semiconducting nanowire-field effect transistors (NW-FETs) hold particular promise, though contemporary NW approaches are inadequate for realistic applications. We present an approach using complementary metal-oxide-semiconductor (CMOS) technology that has not only achieved unprecedented sensitivity, but simultaneously facilitates system-scale integration of nanosensors for the first time. This approach enables a wide range of label-free biochemical and macromolecule sensing applications, including cell type discrimination through the monitoring of live, stimulus-induced cellular response, and specific protein and complementary DNA recognition assays. An important achievement is the introduction of real-time, unlabeled detection capability, allowing for fundamental studies of cellular activation, and specific macromolecule interactions at femtomolar concentrations.
Microlaser
Hui Cao, Professor, Department of Applied Physics and Physics
Microlaser is a laser of size on the order of optical wavelength. It not only has important application in integrated photonic circuit, but also is a model system for the study of cavity quantum electrodynamics. In this talk, I will review our recent progress on microcavity lasers, including the realization of a chaotic microcavity laser with low threshold and unidirectional emission, and the fabrication of a subwavelength microdisk laser.
February 13
Approaching the quantum limit of amplification with Josephson microwave circuits
Michel Devoret, Professor, Department of Applied Physics and Physics
Quantum Mechanics puts a limit on how small the degradation of information passing through an amplifier can be. It is known theoretically that the minimum noise added by an "op-amp"-like amplifier to the signal amounts at least to half a photon at the signal frequency. Can we develop a practical amplifier working at microwave frequencies that would approach this quantum limit? We will present a new amplifier which is based on a ring of four Josephson tunnel junction. Unlike the SQUID, which is powered by a DC source, our amplifier is powered by an RF source, but its backaction noise is minimal. Our results can immediately be applied to the readout of solid state qubits, and, on a longer time scale, to the measurement of very weak signals in various areas of science.
Protein Folding on Rugged Energy Landscapes
Corey O'Hern, Associate Professor, Department of Mechanical Engineering and Physics
We employ coarse-grained molecular dynamics simulations to interrogate the folding kinetics of model proteins following temperature jumps. We are interested in determining to what extent the folding kinetics, measured using the mean-square displacement from the initial conformation, is affected by different initial conformations and folding pathways in the energy landscape. We find that the folding kinetics are generically subdiffusive in systems with `rugged' energy landscapes. We also outline future work in which we will calculate the subdiffusion exponents based on the number of distinct energy minima (or distinct conformations) available to the protein during folding.
January 30
Recent Advances in Chiroptical Spectroscopy
Patrick H. Vaccaro, Professor, Department of Chemistry
The concept of chirality permeates all of science, playing pivotal roles in chemistry, biology, and physics. Electromagnetic radiation propagating through a medium possessing such “intrinsic handedness” experiences a complex index of refraction that differs in real ( ) and imaginary ( ) parts for the two polarization states comprising the helicity (or circular) basis. The resulting phenomena of circular birefringence (CB for ) and circular dichroism (CD for ) lead to discernable effects in the form of nonresonant (linear) polarization rotation and resonant (circular) differential absorption, respectively. In principle, the molecules of opposite handedness comprising an enantiomeric pair can be discriminated by their unique chiroptical signatures; however, the a priori correlation of a specific chiroptical response with an individual enantiomer still presents formidable challenges. This presentation will highlight ongoing efforts to interrogate the electronic optical activity of isolated chiral molecules, with special emphasis directed towards the influence of intrinsic and extrinsic perturbations. Requisite solvent-free measurements have been made possible by our development of Cavity Ring-Down Polarimetry (CRDP), an ultrasensitive polarimetric scheme that has permitted the first quantitative analyses of CB to be performed in rarefied media. Aside from unraveling the complex processes that mediate chiroptical behavior in condensed media, this work has provided a critical assessment for emerging computational predictions of optical activity and for their promising ability to assist in the determination of absolute stereochemical configuration.
Light Force Device Continued: Levitation, Synchronization and Entanglement
Hong Tang, Assistant Professor, Department of Mechanical and Electrical Engineering
Recently we demonstrated the first exploitation of light forces on a silicon platform. We prove that this light force can be further enhanced by photonic modal engineering and by employing photonic cavity and slow light structures. Such strong optomechanical coupling promises a new class of light force devices that allow the investigation of a range of interesting classical and quantum mechanical phenomena. In this talk, we will report our most recent progresses on the development of light force devices, for applications in both classical and quantum regime.
Fall 2008
December 5
Atom-by-atom deconstruction and correlated functional imaging of semiconductor nanowires and devices
Lincoln Lauhon, Assistant Professor, Department of Materials Science and Engineering, Northwestern University
Semiconductor nanowires show great promise as multifunctional components in emerging technologies and provide new opportunities to explore the physics of electrons in reduced dimensions. The continued advancement of nanowire-based materials and technologies depends critically on knowledge and control of their atomic-scale structure, as compositional fluctuations as small as a single dopant atom can affect their properties. Recently, we have made significant advances in quantitative nanoscale characterization that can provide a rational basis for engineering new or improved technologies based on semiconductor nanowires. Specifically, we have used atom probe tomography (APT) to map the distribution of dopant atoms in individual vapor-liquid-solid grown Si and Ge nanowires. We find that the doping efficiency is, in general, lower than expected, and that the dopant distribution can be radially non-uniform, which has important implications for device performance and modeling. Quantitative potential profiles extracted from scanning photocurrent microscopy measurements confirm intrinsic variations in carrier concentration associated with non-uniform doping, and establish the operating principles of nanowire field effect transistors. APT was also used in conjunction with scanning transmission electron microscopy to investigate catalyst atom incorporation in VLS-grown nanowires. Single Au atoms have been detected for the first time at levels above the equilibrium solubility. Diameter-dependent measurements of minority carrier diffusion lengths establish, however, that the nanowire surface controls the minority carrier lifetime. By integrating the activities of nanowire synthesis, composition characterization, and quantitative nanoscale property measurement, we aim to determine the extent to which the properties of semiconducting nanowires can be rationally controlled by doping and composition modulation on the nanoscale.
November 21
Magnetic Liquids for Lab-on-a-Chip and Rapid Diagnostics Applications
Hur Koser, Assistant Professor of Electrical Engineering
Ferrofluids (stable colloidal suspensions of magnetic nanoparticles) offer attractive alternatives to moving mechanical components in industrial machinery. When made biocompatible, they are also used in dilute forms as contrast agents for magnetic resonance imaging, or as drug delivery platforms. Recently, we have proposed and begun implementing a series of biological sensing and cellular manipulation platforms, all based on what we call “ferro-microfluidics”. Our approach involves creating localized magnetic fields within microfluidic devices to actuate ferrofluids. The long term goal is to create assays that are portable, cheap, disposable, rapid and completely labor-free. Ferro-microfluidics offers a practical solution to overcoming the diffusion barrier in micro- and nano-scale biosensor assays. In this talk, we present some of the exciting results that depict our progress to date.
Computational Research Needs for Renewable and Alternative Energy:
Studies of Natural and Artificial Photosynthesis
Victor Batista, Professor of Chemistry
This talk will present recent advances in experimental and computational studies towards the development of rigorous models of catalytic sites for water splitting. The presentation will be focused on the oxygen evolving complex of photosystem II and recent progress by the Yale Energy Group ( c-PI's: Batista, Brudvig, Crabtree and Schmuttenmaer, http://www.chem.yale.edu/~green) on studies of biomimetic catalytic systems for artificial photosynthesis.
November 12
Nanotechnology for energy harvesting: from nanogenerators to nanopiezotronics
Professor Zhong Lin Wang, School of Materials Science and Engineering Georgia Institute of Technology
Exploring renewable, sustainable and green energy resources is the most critical challenge to sustainable development of human civilization. At the large-scale, besides the well known energy resources that power the world today, such as petroleum, coal, hydraulic, natural gas and nuclear, active research and development are being taken in exploring alternative energy resources such as solar, geothermal, biomass, nuclear, wind, and hydrogen. At a much smaller scale, energy and technologies are desperately needed for independent and continuous operations of implantable biosensors, ultrasensitive chemical and biomolecular sensors, nanorobotics, micro-electromechanical systems, remote and mobile environmental sensors, homeland security and even portable personal electronics. A nanorobot, for example, is proposed to be a smart machine that may be able to sense and adapt to the environment, manipulate objects, taking actions and perform complex functions, but a key challenge is to find a power source that can drive the nanorobot without adding much weight. An implanted wireless biosensor, for example, requires a power source, which may be provided directly or indirectly by charging of a battery. It is highly desired for wireless devices and even required for implanted biomedical devices to be self-powered without using battery. Therefore, it is desperate to develop nanotechnology that harvests energy from the environment for self-powering these nanodevices. This talk will focus on nanotechnologies that have been developed for harvesting energy from our living environment with a focus on mechanical energy. An introduction will be given about nanogenerators for generating electricity using sonic waves and body movements. Finally, a new field on nano-piezotronics will be introduced, which uses piezoelectric-semiconducting coupled property for fabricating novel and unique electronic devices and components.
November 7
Beyond Si: Future CMOS Technologies
Tso-Ping Ma, Professor of Electrical Engineering
Several leading contenders for the mainstream post-Si CMOS technology, including carbon nano-tube, graphene, and III-V semiconductors, have been evaluated, and the author’s assessment will be presented. The effects of high carrier mobility and low density of states on transistor's performance will be discussed. Some promising state-of-the-art non-Si transistor data will be reviewed. A novel "unipolar" CMOS logic concept will be introduced.
Greener Approaches to Semiconductor Nanoparticle Syntheses
Jack Faller, Professor of Chemistry
Bisphosphineselenides are nonvolatile crystalline solids. Our new synthetic procedure using P^P=Se ligands for semiconductor nanoparticle preparation avoids the use of toxic and volatile selenium and dimethylcadmium precursors. 31P NMR studies have provided information on the nature of precursor complexes. Wavelengths of absorption and emission of products are indicative of size dependence typical of quantum dots.
October 31
Nanosculpting and Nanoelectronics
Marija Drndic, Professor of Physics, University of Pennsylvania
Manipulation of matter on the scale of atoms and molecules is an essential part of realizing the potential that nanotechnology has to offer. In this talk I will describe transmission electron beam ablation lithography (TEBAL), a method for fabricating nanostructures and fully integrated devices by nanosculpting matter with electron beams. TEBAL works by controllably exposing materials to an intense and highly focused beam of electrons inside the transmission electron microscope (TEM). The effect of electron irradiation can be used to controllably displace or ablate regions of the material, such as thin metal films and graphene sheets, with resolution on the scale of tens of atoms per exposure. In situ TEM imaging of the ablation action with atomic resolution allows for real-time feedback control during fabrication. Specific examples that I will present include the fabrication and characterization of nanogaps, nanorings, nanowires with tailored shapes and curvatures, and multi-terminal devices with nanoislands or nanopores between the terminals. The combination of high resolution, geometrical control and yield make TEBAL attractive for many applications. In particular, I will discuss the impact of this work in nanoelectronics, nanofluidics and molecular translocation studies through nanopore-based transistors.
October 24
Biological Sensors and Switches Made of RNA
Ron Breaker, Molecular, Cellular and Developmental Biology;
Molecular Biophysics and Biochemistry
Cells control the expression of thousands of genes in response to many chemical and physical signals. Until recently, it was believed that proteins were almost exclusively used to detect biological signals and then switch on or off the various genes needed to respond to these signals. However, numerous examples of “riboswitches” have been discovered that act as chemical sensors and as genetic switches. Most riboswitches have been discovered in bacteria, where they control approximately 3% of the genes in some species. Examples of riboswitches also exist in plants and fungi, where they control gene expression by regulating the processing of messenger RNAs.
Although riboswitches are often considered to be of ancient origin, and therefore primitive compared to protein factors, riboswitches also appear to be capable of functioning as sophisticated genetic switches that permit surprising levels of molecular recognition and regulatory complexity. In simple riboswitches, a single aptamer that senses as single chemical compound often is sufficient for proper control of certain genes. However, we have discovered that some riboswitches carry multiple aptamers and display characteristics that are much more complex. For example, some tandem riboswitches exhibit Boolean logic functions. These findings support the view that sophisticated gene control systems can exist without the need for protein factors, and that an “RNA World” might have existed billions of years ago.
Persistent Currents in Resistors: How Wrong Can Ohm's Law Be?
Jack Harris, Physics & Applied Physics
One of the most remarkable predictions of the quantum theory of electronic circuits is that a small loop of non-superconducting metal can have a circulating current flowing in it in the absence of any applied voltage.
This "persistent" current is directly analogous to the orbital angular momentum of electrons in atoms, and the prediction they could be observed in realistic devices at accessible temperatures generated considerable excitement. In the past twenty years the handful of experiments in this area have produced confusing results, many of which are at odds with theory and even other experiments. In an effort to address the controversies which have arisen, we have developed a new type of detector for persistent currents which offers greater sensitivity and a less-invasive measurement than was previously possible. I will describe our approach to this problem, and our measurements of persistent currents.
October 10
Polyelectrolyte nanofilm assembly under an applied electric potential
Paul Van Tassel, Chemical Engineering
Interactions between charged macromolecules (e.g. proteins, nucleic acids, polyelectrolytes) and charged surfaces govern many natural and industrial processes. We report here on the influence of an applied electric potential on the adsorption kinetics of charged polymers, focusing on the following significant result: the adsorption of certain amine side chain-containing polycations may become continuous, i.e. asymptotically linear (or nearly linear) in time over hours, upon the application of a modest anodic potential. We discuss the influence of important control variables (substrate potential, pH, ionic strength) on the continuous adsorption process, and propose a mechanism based on polymer-polymer binding -- enabled by suppressed electrostatic repulsion and/or enhanced ionic correlations near the conducting surface and stabilized by short-range attractive interactions -- leading to interfacial charge regulation. Continuous adsorption under an applied electric potential offers the possibility of nanoscale films of tailored polymer content realized in a single step.
Novel Approaches to Spin Control: From Qubits to Skull and Bones
Sean Barrett, Physics & Applied Physics
Abstract: Pulses are a fundamental tool used broadly throughout magnetic resonance (NMR, MRI, ESR), in atomic physics, and more recently in quantum information processing. In this talk, we show how the tiny difference between hard Pi pulses and their delta-function approximation can be exploited as a new resource to control coherence, enabling novel classes of spin echoes with promising applications in NMR, MRI of solids, and beyond. These novel echoes, which were discovered during basic research on quantum information physics, open a new route to magnetic resonance imaging (MRI) or MR microscopy of solids in a constant field gradient, including short T2 tissues such as teeth and bone. Possible applications will be discussed.
Reference: ”Controlling Coherence Using the Internal Structure of Hard pi Pulses”, Yanqun Dong, R. G. Ramos, Dale Li, and S. E. Barrett, Phys. Rev. Lett. 100, 247601 (2008).
September 26
Probing Transient Photoconductivity in Nanostructured Materials using Time-Resolved Terahertz Spectroscopy, Part II
Charles Schmuttenmaer, Chemistry
Time-resolved THz spectroscopy (TRTS) is a non-contact electrical probe capable of measuring the photoconductivity on a sub-ps to nanosecond (ns) timescale. In this talk, TRTS is employed to determine the transient photoconductivity of ZnO/TiO2 core-shell nanoparticles, TiO2 nanotubes, and dye-sensitized nanocrystalline colloidal TiO2 films. Electron injection occurs on sub-ps time scales. Decay kinetics (on hundreds of ps to ns time scales) indicates that surfaces and interfaces are the dominant sources of recombination. The photoconductivity deviates strongly from Drude behavior and is explained by disorder-induced carrier localization and/or backscattering of the photogenerated carriers. Trends as a function of material and morphology will be discussed.
Superconducting Quantum Sensors for Astronomy: New Tools and Possibilities
Dan Prober, Applied Physics
Recent advances in nano- and micro-fabrication and quantum circuit
engineering have provided new concepts and devices for astronomers, who
are eagerly employing these devices for new observations. We describe
recent work at many labs that are working in this field, and current research at Yale.
September 12
Three-Dimensional Atomic Force Microscopy: Probing Short-Range Chemical Forces with Picometer Resolution
Udo D. Schwarz, Mechanical Engineering
Site-specific surface chemical interactions govern numerous scientific and technological fields including catalysis, thin film growth, and tribology. Full control over the design process in these fields requires not only atomic-scale structural information, but also a quantitative, site-specific elaboration of the surface force field. Until now, such information has only been theoretically accessible.
Here we demonstrate a new atomic force microscopy-based approach to experimentally obtain this data. As an application, we show force maps with picometer spatial resolution and piconewton force resolution obtained on graphite that allow a detailed characterization of the distance-dependent surface-probe interactions. Graphite has been chosen due to its astonishing but still poorly understood qualities as a solid lubricant as well as its suitability as a model system for multilayer sp2-bonded graphene sheets, which have recently attracted interest because of their extraordinary electronic properties. The new method is, however, broadly applicable to problems where atomic-scale knowledge of local interactions is beneficial.
Nanostructured Polymeric Materials for Energy Storage and Harvesting
Jodie Lutkenhaus, Chemical Engineering
Polymeric materials for energy storage and harvesting are increasingly important because of their low cost, relative flexibility, and tunable functionality. Designing such materials at the nanoscale imparts greater transport and electrical properties leading to increased performance and efficiency. This talk highlights two distinct efforts in using nanostructured polymeric materials for energy storage and harvesting. The first effort uses layer-by-layer (LbL) assembly to create thin film electrolytes for Li-ion batteries. The second effort uses nanotemplating to create ferroelectric and piezoelectric poly(vinylidene fluoride)-based nanowires.
Spring 2008
May 9
The Development of “Smart” Magnetic Solders
Ainissa G. Ramirez, Mechanical Engineering
Magnetic solders are a new class of magnetorheological materials or “smart fluids.” The suspension of micron-sized magnetic particles in tin-silver solders enables them to respond to magnetic fields. This ability to manipulate solder has several potential microfabrication applications: specifically, the filling of vertical paths and other hard-to-reach regions. Self-healing structures based on these materials could potentially be repaired in service by the application of heat and a magnetic field. The inclusion of magnetic particles has also been found to drastically increase the solder’s strength. In addition to these practical issues, these magnetically-responsive solders are a compelling tool for microfabricating adaptable and complex 3D geometries. This talk will describe the synthesis, mechanical behavior, and applications of these new materials.
Targeting the foreign body response via biomaterial-based drug
and gene delivery
Themis Kyriakides, Pathology
The implantation of biomaterials into soft tissues leads to the development of the foreign body response (FBR) that can interfere with the function of the implant and eventually lead to implant failure. In general, due to the FBR a largely avascular and dense collagenous capsule forms around biomaterials and scaffolds. A hallmark of the FBR is the formation and persistence of foreign body giant cells (FBGC) on the surface of the implant, a process that is indicative of a chronic inflammatory response. In addition, FBGC have been shown to cause extensive surface damage to a variety of biomaterials and cause the release of microparticles that can have toxic effects. Furthermore, a role for FBGC in promoting biomaterial encapsulation has been proposed. Thus, unlike a wound healing response that is self-limiting, the FBR can last for the duration of the implantation period. Despite the prominence of FBGC at implantation sites, little is known about their formation in vivo.
Through our work, we have identified several intracellular and extracellular modifiers of various aspects of the FBR including FBGC formation. Furthermore, we have developed localized drug and gene delivery strategies to target molecules that are essential for the development of the FBR. These include the angiogenesis inhibitor thrombospondin-2, a matrix-degrading enzyme (MMP-9), a chemokine (MCP-1), and a small GTPase (Rac1). Modulation of the expression or activity of these molecules suggests that a shift towards a wound healing-like response is possible and can lead to enhanced biocompatibility by preventing damage and extending the lifespan of implants.
May 2
Transmission Electron Microscopy with High Spatial, Temporal
and Spectroscopic Resolution
Nigel D. Browning, Professor of Materials Science, Department of Chemical Engineering and Materials Science, University of California-Davis
The last few years have seen a paradigm change in (scanning) transmission electron microscopy with unprecedented improvements in spatial, spectroscopic and temporal resolution being realized by aberration correctors, monochromators and pulsed photoemission sources. Spatial resolution now extends to the sub-angstrom level, spectroscopic resolution into the sub-100meV regime, and temporal resolution to the nanosecond scale. However, while these instrumentation developments have brought notable successes in materials analysis, they have also challenged the established experimental protocols and our fundamental understanding of both imaging and spectroscopy in the (S)TEM. In this presentation, examples of where the new instrumentation has successfully been used to address materials issues in nanoscale systems will be described. Additionally, the challenges associated with the routine use of the new (S)TEMs for reliable quantitative imaging and spectroscopy will be discussed. Finally, a personal perspective on the upcoming technology that will shape (S)TEM experimental capabilities in the next few years will be presented.
April 25
DNA-Guided Nanoassembly: Synthetic Biology Using an Orthogonal Genetic Code Where DNA-Makes-Protein
Paul M. Lizardi, Pathology
Abstract TBA
Did Life Grind to a Start? A Brief History of the Origins of Homochirality
J. Michael McBride, Chemistry
Ever since Pasteur discovered the handedness of natural molecules 160 years ago, there has been a nagging question: How was symmetry broken so that life on Earth came to use D-sugars and L-amino acids and not their mirror images? After surveying approaches to this question by chemists, physicists, biologists, statisticians, and geologists at 50-year intervals, this talk concludes with evidence published in February showing that grinding a slurry of mirror-image crystals converts their molecules to a single hand. John Tully and I advocate an amplification mechanism that depends on saving subcritical, chiral clusters from dissolution by means of their intact incorporation into larger crystals of the same hand.
April 11
Nanomechanical Devices Riding Optical Forces
Hong Tang, Mechanical and Electrical Engineering
Optical forces are generally thought to be too weak for practical use. This picture changes when applied to lightweight nanoscale devices. In this talk, we demonstrate that significant optical force can be produced by a single pass of light in a silicon photonic circuit. This optical force, originated from lateral photon confinement rather than from momentum transfer, is applied in a planar geometry and offers high scalability. Control and harnessing optical force will allow solid state devices to operate under new physical principle, and open doors to non-charge based classical and quantum devices. Practical application enabled by this strong mechanics-photonics interaction, such as all-optical logic, reconfigurable photonics, mechanical nonlinear optics, ultrasensitive transducers, will be discussed.
Designed Synthesis of Uniform Property Single-Walled Nanotubes of Carbon, Boron and GaN for Biomedical, Superconductivity and Solar Harvesting Applications
Lisa Pfefferle, Chemical Engineering
The ability to produce a selected structure carbon nanotube by design during synthesis is an important goal to enable applications. For example, electronic properties are a strong function of diameter and structure ((n,m) identity) with approximately 2/3 of SWNT formed in most processes being semi conducting and 1/3 metallic. Small diameter nanotubes are particularly interesting as their strong radius of curvature leads to increased reactivity. Since, cleaning/separation can introduce defects and change properties, selective synthesis is crucial. Achieving selectivity for (n,m) synthesis of SWNT is one of the holy grails for nanotube research. I will show how the diameter and structure of a carbon nanotube can be controlled through designed synthesis and how understanding carbon nanotube growth led to our synthesis of the first pure boron and GaN single-walled nanotubes. Applications we have demonstrated for each system will be discussed along with the remaining challenges in the synthesis to optimize the performance of these applications.
March 28
Chemical dynamics at metal and nanoparticle surfaces
John Tully, Chemistry
The adiabatic (Born-Oppenheimer) approximation underlies most of our understanding of molecular dynamics. It is becoming clear, however, that this approximation is often inadequate to describe atomic motions at metal surfaces and metal nanostructures; nonadiabatic behavior is the rule rather than the exception. Electron-hole pair transitions, charge transfer and hot-electron-induced motion can be dominant pathways for energy flow and can drastically alter the pathways of atomic motion. This talk will present progress toward a unified picture of nonadiabatic dynamics at metal surfaces. Initial applications to multi-quantum vibrational-to-electronic energy transfer in scattering of nitric oxide from gold and creation of excited electrons in the CO oxidation reaction on a platinum nanodiode will be presented.
Strain engineering of SiGe for photovoltaics, nanoelectronics, and nanostructured thermoelectric materials
Minjoo Larry Lee, Electrical Engineering
SiGe alloys were first studied in the 1960s for use in radioisotope thermoelectric power generators in deep-space satellites. Since then, SiGe has become prevalent in CMOS manufacturing due to its use in high-speed strained Si technology. In this talk, I will introduce three aspects of strain engineering in SiGe: engineering of the strain relaxation process, MOSFET channel engineering using strained Si, SiGe, and Ge, and the use of strain-driven Stranski-Krastanov nanodots for reduction of thermal conductivity. I will also discuss examples of how strain-engineered SiGe can be applied to a broad range of electrical and optoelectronic devices, including high-efficiency photovoltaics, high-speed MOSFETs, and next-generation thermoelectric materials.
March 14
Student Poster Session
February 29
Biotitanification
Ann Valentine, Chemistry
Many organisms produce or employ inorganic minerals for mechanical support or protection, for metal storage or detoxification, or as instruments, weapons, or sensor components. Although titanium minerals are prevalent in the environment, titanium is not usually considered a bioactive element, and instances of its association in mineral form with organisms are very few. One example is that titanium occurs at up to 1254 ppm in the acid-resistant siliceous frustules of diatoms. We wondered whether the biomolecules that induce nanostructured silica formation, also called biosilicification, might also produce titanium minerals, whether this process could be used to make materials of controlled morphology, and whether proteins could be immobilized in the materials. Naturally occurring polyamines spermidine and spermine are analogs of the species-specific polyamines found in diatoms. These molecules, as well as poly(allylamine) (a mimic of longer biopolyamines) and the R5 peptide (a repeat unit of a silaffin protein isolated from a diatom) induce the formation of mineralized nanostructured titanium from soluble titanium(IV) precursors.
Trapping Protons and Electrons on Little Chunks of Water: Using Size-Selected Cluster Ions to Capture Molecular Level Aspects of Water at Work
Mark Johnson, Chemistry
When an elementary electric charge is forced onto a collection of water molecules, only a select few molecules do the heavy lifting in accommodating the excess charge. The ability of an excess charge to compromise the molecular integrity of a single water molecule is quite different for protons and electrons. These differences are manifest as distinct shapes in the emerging water "crystal" upon addition of the first few hydration shells, where the size of the cluster indeed changes the local charge accommodation motif. We use size-selected vibrational spectroscopy to understand the structural consequences of charge accommodation, where we combine laser spectroscopy with free-jet ion sources and mass spectrometry. Unexpected (but welcome!) practical implications of these molecular-level measurements for understanding charge transport in biological processes (trans-membrane proton pumps) and solar energy conversion (proton exchange membranes) are discussed.
February 15
Title TBA
Robert Schoelkopf, Applied Physics
Abstract TBA
MEMS Electrosprays for Versatile Nanoparticle Synthesis
Alessandro Gomez, Mechanical Engineering
The generation of nanoparticles with narrow size distributions at flow rates adequate for a variety of applications is the ultimate goal of all synthesis approaches. Our research focuses on the use of the electrospray in the so-called cone-jet mode for a variety of applications requiring nanoparticle synthesis and coatings. This technology has the unique capability of producing monodisperse droplets/particles over a wide size range, from a few nanometers to several micrometers, depending on liquid flow rate, applied voltage and liquid electric conductivity. With appropriate selection of the liquid formulation, the droplets after evaporation and/or chemical reaction ultimately yield either nanoparticles residues of controlled and narrow size distribution or uniform deposits. The electrospray had a dramatic technological impact in the field of analytical chemistry, leading to the awarding of the 2002 Chemistry Nobel Prize to John B. Fenn, for his pioneering work at Yale. Its widespread application to other fields has been hampered by two drawbacks: first and foremost, low flow rates, and, to a lesser extent, restrictions on the physical properties of the liquids that can be electrosprayed. I will discuss key aspects of the research in our group that is aimed at: i) increasing by orders of magnitude the liquid flow rate to be dispersed, without compromising the quasi-monodispersity of the generated droplets; ii) extending the technique to a broad range of liquids by using a twin fluid approach, in which one fluid that is well suited to being electrosprayed “drags” the second fluid, that is compatible with a given applications but could not be otherwise electrosprayed; and iii) using this technique in a variety of high-value-added applications.
February 1
Computational and Experimental Study of Diffusion Flames
Mitchell Smooke, Mechanical Engineering
Our research has centered on an investigation of the effects of complex chemistry and
detailed transport on the structure and extinction of hydrocarbon flames in coflowing
axisymmetric configurations. We have pursued both computational and experimental
aspects of the research in parallel. The computational work has focused on the application
of accurate and efficient numerical methods for the solution of the boundary value
problems describing the various reacting systems. Detailed experimental measurements
have been performed using two-dimensional imaging techniques. Spontaneous Raman
scattering and laser-induced fluorescence have been used to measure the temperature,
major and minor species profiles and Laser-induced incandescence has been used to
measure soot volume fractions. Our goal has been to obtain a more fundamental
understanding of the important fluid dynamic and chemical interactions in these flames
so that this information can be used effectively in combustion modeling. In this talk we
will discuss the development and application of the model and diagnostics to both sooting
and nonsooting diffusion flames at atmospheric pressure. We will discuss issues related
to flame lift-off, soot distribution, and NOx formation.
Active Photonic Nanomaterials
Hui Cao, Applied Physics
Active photonic nanomaterials, which have high gain or large nonlinearity, are essential to the development of nanophotonic devices and circuits. In this talk, I will provide a review of our recent research activities related to the fabrication of active photonic nanomaterials and the development of photonic devices based on such materials. In particular, we focus on a wide bandgap semiconductor zinc oxide and fabricate a broad range of structures, from disordered to periodic, with various nanofabrication techniques. Lasing in the near-ultraviolet frequency has been realized in both periodic and random structures at room temperature under optical pumping.
January 18
Ab Initio Theory of Micro and Nanolasers
A. Douglas Stone, Applied Physics
Progress in the fabrication of micro and nanostructured lasers has led to a number of novel and complex laser designs. Among these are circular and deformed microdisk lasers, photonic crystal defect lasers and random semiconducting nanolasers. These complex laser designs have highlighted the shortcomings of conventional laser theory, which is based on relatively simple one-dimensional laser cavities, and assumes the lasing modes are resonances of the passive cavity (without gain). Recently we have developed a time-independent theory which can treat quantitatively and predictively lasers with arbitrarily complex cavity design and any degree of outcoupling. We sketch the main ideas of the theory and show results from application to edge-emitting, disk and deformed disk lasers, and to random lasers.
Polar Molecules as Quantum Tools
David DeMille, Physics
Our group has devised a set of ideas for using the internal quantum states of simple molecules as the building block for obtaining complete control over a complex quantum system. A wide set of many-body quantum states can in principle be engineered from the bottom up, by manipulating the dipolar couplings between polar molecules. In order to implement these ideas, it is necessary to control not only the internal (rotational, vibrational) states of molecules, but also their motion. We are developing techniques for cooling molecules to extremely low temperatures (~10 microKelvin or lower), trapping them, and then manipulating their internal states. This talk will describe some of the basic ideas for quantum engineering using polar molecules, as well as our currents experimental progress.
Fall 2007
September 14
Erin Lavik, Biomedical Engineering
(Abstract TBA)
Folded Proteins Devoid of Alpha Amino Acids
Alanna Schepartz, Chemistry & Molecular Cellular and Developmental Biology
Non-natural polymers have the capacity to recapitulate both the well-folded structures and resultant functionalities of biological polymers. Peptides composed of ß3-amino acids, which have one additional backbone methylene unit compared to natural a-amino acids, can adopt stable helices in water and interact with cellular proteins and membranes. This lecture will describe the x-ray structures and solution phase kinetic and thermodynamic properties of a series of ß-peptides that self-assemble spontaneously in aqueous solution into highly thermostable ß-peptide bundles.
September 28
Magnetic Liquids for Lab-on-a-Chip and Rapid Diagnostics Applications
Hür Köser, Electrical Engineering
Ferrofluids are stable colloidal suspensions of nanosize ferromagnetic particles in either aqueous or oil-based media. They have found their way into a variety of applications, such as sealing, damping and blood separation; in dilute, functionalized forms, they have also been used as drug delivery and MRI contrast agents. These complex liquids offer attractive alternatives to moving mechanical components in miniaturized cooling, pumping and integrated micro-total-analysis-systems for chip-scale chemistry and biology. Water-based ferrofluids can also be made bio-compatible, rendering them useful in novel cell manipulation and sorting schemes. We have recently proposed, modeled and experimentally confirmed that ferrofluids can be actuated and pumped in closed-loop geometrics, even within geometries of micro-scale devices. The pumping dynamics depend on the average nanoparticle size within the ferrofluid. If particles are functionalized with a receptor molecule, the entire volume of the ferrofluid becomes a pathogen sensor that can detect minute quantities of target antigens efficiently and effectively. We are working on creating portable, disposable, cheap and miniaturized sensor and diagnostic devices based on this dynamic effect. We also briefly report on the development of a novel, ferrofluid-based cellular manipulation platform and a new assay to study a large quantity of ligand-receptor interactions quickly and simultaneously, without the need for any wash cycles.
Polyelectrolyte Nanofilm Biomaterials
Paul Van Tassel, Chemical Engineering
Emerging biomedical therapies and devices demand cell-contacting biomaterials meeting increasingly stringent criteria. Candidate materials must exhibit precisely controlled bulk properties (structure, mechanical moduli, degredation rate, etc.), while also presenting a surface capable of promoting a favorable cellular response. Designing materials to meet both bulk and surface requirements presents an enormous challenge. Nanofilm biomaterials are attractive in this regard as they potentially allow for the decoupling of bulk and surface properties. The idea is to place a thin film (ca. 10-100 nm), chosen for its cell-contacting properties, onto the surface of a biomaterial, chosen for its bulk properties. We discuss here the formation of nanofilm biomaterials through layer-by-layer assembly, various strategies toward controlling their cell-contacting properties, and examples showing their potential as tissue engineering substrates. We also introduce a new method of nanofilm formation, based on deposition under an applied electric potential, enabling single component films of arbitrary thickness to be grown in a single step.
October 12
Heteropolymer Dynamics and Random Walks on a Lattice: Course-Grained Computer Simulations of Protein Folding and Unfolding
Corey O'Hern, Mechanical Engineering & Physics
We perform computer simulations of simple polymer models to elucidate important questions concerning the structure of native and denatured proteins and the dynamics of protein folding. We will focus on two key open questions. First, what is the structure of the denatured state of proteins? A. L. Cortajarena and Lynne Regan (Yale MB&B) and coworkers have performed experiments on modular repeat proteins and find that denatured proteins can be significantly more compact than that expected for structureless linear polymers. Simulations of simple polymer lattice models confirm this result and suggest that attractions are necessary to give rise to the amount of compaction seen in experiments. The second question is focused on the connection between the protein's amino acid sequence and the folding pathway of the protein. Can we predict whether a given protein undergoes a quick, one-step folding process, passes through one or several intermediate states before reaching the native state, or becomes trapped in one of many glassy states that have nearly identical energies. We will use a combination of molecular dynamics simulations and single-molecule experiments (Elizabeth Rhoades, MB&B) on short peptides to understand the link between amino acid sequence and folding pathways.
Nanotubes by Example: Carbon, Gallium Nitride, and Boron
Sohrab Ismail-Beigi, Applied Physics & Physics
Carbon nanotubes are probably one of the best known examples of nano-materials, although atomically-thin nanotubes of other elements are now fabricated. Theoretically, nanotubes are constructed by rolling up a two-dimensional sheet-like material into tubular form. Hence, they provide ideal cases for studying nanoscopic effects: e.g., geometric and quantum confinement of electrons, enhanced Coulomb interactions, curvature effects, and novel bonding schemes in two dimensions. We provide some examples based on our recent theoretical work on carbon, gallium nitride, and boron nanotubes.
October 26
Probing Transient Photoconductivity in Nanostructured Materials using Time-Resolved Terahertz Spectroscopy
Charles A. Scmuttenmaer, Chemistry
The microscopic details of carrier transport in nanocrystalline colloidal thin films is required for complete understanding of a variety of photochemical and photoelectrochemical cells utilizing interpenetrating networks. Measuring the photoconductivity and charge transport properties in these materials, however, is a challenging problem because of the inherent difficulty of attaching wires to nanometer-sized objects. Furthermore, picosecond (ps) carrier dynamics play an important role in efficient charge separation and transport, but the low temporal resolution of traditional methods used to determine the photoconductivity precludes their use in studying sub-ps to ps dynamics. Time-resolved THz spectroscopy (TRTS), on the other hand, is a non-contact electrical probe capable of measuring the photoconductivity on a sub-ps to nanosecond (ns) timescale. In this talk, TRTS is employed to determine the transient photoconductivity of ZnO nanowires, polycrystalline, and nanoparticle films, as well as dye-sensitized nanocrystalline colloidal TiO2 films. Electron injection occurs on sub-ps time scales. Decay kinetics (on hundreds of ps to ns time scales) indicate that surfaces and interfaces are the dominant sources of recombination. The photoconductivity deviates strongly from Drude behavior and is explained by disorder-induced carrier localization and/or backscattering of the photogenerated carriers. Trends as a function of material and morphology will be discussed.
Interaction of Bacteria with Carbon Nanotubes
Menachem Elimelech, Chemical Engineering
Recent and ongoing work in our lab on the interaction of well characterized single-walled and multi-walled carbon nanotubes with bacterial (E. coli) cells will be presented. Direct contact of bacterial cells with the carbon nanotubes results in significant cell damage and loss of viability, as verified by several independent techniques. Single-walled carbon nanotubes exhibit a much stronger antibacterial activity than multi-walled carbon nanotubes. Possible mechanisms for the inactivation of the bacterial cells upon contact with the carbon nanotubes are discussed. The results point out to the potential biotoxicity of carbon nanotubes in aquatic environments. The finding may also be useful in the application of carbon nanotubes as building blocks for antimicrobial materials.
November 9
III-Nitride Nanowires: Heterostructures, Epitaxial Alignment, and Applications
Jung Han, Electrical Engineering
Most of NWs are prepared by catalytic VLS method on amorphous or polycrystalline substrates. The as-grown, hay-stack like NWs are dispersed randomly onto target wafers where electrical contacting and/or characterizations are performed. The purpose of this paper is to demonstrate a hybrid approach toward the construction of GaN NW arrays and networks through the use of (optical) lithographically-defined selective-area growth (SAG) and bottom-up VLS synthesis. Spatially ordered and flexibly patterned NW networks are prepared, in which the stochastic nature in contemporary process of NW synthesis and fabrication is greatly mitigated. Beyond the obvious application in nanoelectronics, the availability of aligned, horizontal nanowires opens up new possibility in nano-electromechanical system (NEMS) application as nanoscale resonators in gravimetric detection with ultrahigh sensitivity. The combination of SAG with nanowire synthesis is expected to provide a new paradigm for nanoscale electronics, photonic, and nano-electromechanical devices.
Characterizing the Shape and Size of Nanoparticles in the Gas Phase
Juan Fernandez de la Mora, Mechanical Engineering
Size, density, and shape are important characteristics of nanoparticles enabling simple indirect tests of their functionality. When the particles are charged and suspended in the gas phase, such tests can be made very fast via electrical mobility (drag) measurements combined with mass spectrometry (or other schemes such as inertial impaction), allowing on-line monitoring during a process of synthesis. In cases where the liquid solvent can be electrosprayed, the same can be done for nanoparticle syntheses proceeding in the liquid phase. The potential of these techniques will be illustrated in various applications from several laboratories. These include for instance the observation of phase changes in individual metal clusters; or the study of loss of stability of the spherical shape in charged polymer particles (or proteins) once their charge exceeds a critical (mass dependent) value; or the determination of the size and density distribution of lipoproteins. One of the features limiting on-line monitoring in aerosol reactors is the low efficiency with which nanoparticles can be charged. This problem arises also in the analysis of vapor species (for instance, low vapor pressure explosives), and can be addressed by high pressure variants of conventional confinement techniques based on RF fields. Size selection in the gas phase at high resolution is a possibility that has not been sufficiently explored, but is theoretically possible under certain circumstances that will also be discussed.
November 30
Molecular Recognition In Catalysis
Robert H. Crabtree, Chemistry
In a biomimetic application based on the way enzymes carry out selective chemistry hydrogen bonding molecular recognition groups appended to terpyridine ligands give manganese based catalysts capable of completely selective conversion of C-H bonds into C-O-H groups at otherwise unactivated remote positions.
Atomic Scale Mechanisms of Surface Phenomena Through Direct Observation
Eric Altman, Chemical Engineering
The development of scanning probe microscopies has made it possible to follow the motions of individual atoms and molecules on surfaces. In my lab, we have built several ultra-high vacuum, variable temperature scanning tunneling microscopes capable of recording movies of surfaces at high resolution at temperatures as high as 900 K. In this talk, I will show how we have been using these instruments to characterize growth mechanisms on semiconductor surfaces, the oxidation and reduction of metal surfaces, and the structure and reactivity of transition metal oxide surfaces. New collaborative directions in chemically sensitive imaging in which tips are functionalized to identify different types of atoms on the surface and to probe the chemical reactivity of different surface atoms will also be discussed.
December 14
Biotitanification
Ann Valentine
Many organisms produce or employ inorganic minerals for mechanical support or protection, for metal storage or detoxification, or as instruments, weapons, or sensor components. Although titanium materials are prevalent in the environment, titanium is not usually considered a bioactive element, and instances of its association in mineral form with organisms are very few. One example is that titanium occurs at up to 1254 ppm in the acid-resistant siliceous frustules of diatoms. We wondered whether the biomolecules that induce nanostructured silica formation, also called biosilicification, might also produce titanium minerals, whether this process could be used to make materials of controlled morphology, and whether proteins could be immobilized in the materials. Naturally occurring polyamines spermidine and spermine are analogs of the species-specific polyamines found in diatoms. These molecules, as well as poly(allylamine) (a mimic of longer biopolyamines) and the R5 peptide (a repeat unit of a silaffin protein isolated from a diatom) induce the formation of mineralized titanium from soluble titanium(IV) precursors.
David DeMille
(Abstract TBA)
Summer 2007
August 17
Nanosystems for Engineering and Detection of Immunity
Tarek Fahmy, Biomedical Engineering
The immune system is made up of a complex network of molecules and cells that can screen its own components, protect itself, and attack invaders, such as bacteria and viruses. Immune system malfunction can result in the genesis of many common chronic, autoimmune, and alloimmune diseases. Failure of this system to recognize pathogens or ever cancer cells can lead to progressive debilitating disease states. The immune system therefore offers a wealth of targets and strategies that need to be understood and modulated. Engineered nanoscale biomaterials may facilitate detection and modulation of immunity. In this discussion, we will focus on the engineering, fabrication and application of nanobiomaterials for applications in understanding, detection and modulation of the immune response.
Parametric Amplification of Quantum Signals with Superconducting Circuits
Michel Devoret, Applied Physics & Physics
Quantum Mechanics puts a limit on how small the degradation of information passing through an amplifier can be. It is known theoretically that the minimum noise added by the amplifier to the signal amounts at least to half a photon at the signal frequency. Is it possible to construct a practical amplifier working at microwave frequencies that would reach this quantum limit? We will present recent work by our group aiming at answering this question, which is of practical importance for the readout of solid state qubits, and, more generally, for the measurement of very weak signals in various areas of science.
July 18
June 15
Spring 2007
May 18
Superconducting Nanodetectors for Studies in Spectoscopy; Astrophysics and Nanotubes
Daniel Prober, Applied Physics
The production of nanoscale superconducting detectors can be accomplished in most major laboratories in the US. This area has been a leading interest at Yale, and has now produced a number of new detectors that are being used in other scientific fields. We explain the operation of these devices and their potential. We also show how the separate concepts can be used to study electromagnetic waves propagating on a single carbon nanotube, in order to explore a regime that cannot be access with other methods.
Proteins: The Ultimate Nanomachines
Lynne Regan, Molecular Biophysics & Biochemistry
Proteins perform a myriad of different functions within all living organisms. They mediate muscle contraction, chromatin condensation, gene expression, hormone-receptor interactions, enzymatic catalysis, and much, much more. In spite of their amazing diversity of function, proteins are all made of linear combinations of the same 20 amino acids, or a subset thereof. The grand challenges are to be able to predict the structure, function and properties of a protein from its amino acid sequence, and to be able to exploit our knowledge of the construction and properties of natural proteins to engineer novel proteins to perform the functions we specify. I will present a snapshot of the current efforts of my group towards meeting these challenges.
April 20
Looking at Ion Channels and Measuring their Currents
Frederick J. Sigworth, Physiology
Ion channels are cell-membrane proteins that control the electrical activity of neurons and many other cell types. Their function can be studied by sensitive electrical measurements using the "patch clamp" technique. Understanding how they respond to stimuli such as transmitter molecules, mechanical stretch and voltage requires the analysis of their structure in their various functional states. First I will describe our efforts toward making the patch clamp technique into a high-throughput screening tool. Second I will describe our efforts to obtain structures of ion-channel proteins, in their "open" and "closed" states, using new methods in high-resolution electron microscopy.
Nanophotonic Probes of Soft and Biological Matter
Eric R. Dufresne, Mechanical Engineering
We exploit surprising properties of light near -- and even below -- the diffraction limit to study and control materials. Optical forces, negligible at the macroscale, can dominate the dynamics of materials at the scale of hundreds of nanometers. I will describe how we harness these effects to measure tiny forces, sort materials, assemble microscale structures and probe the biochemical pathways of live cells. In addition, I will briefly outline our recent efforts to characterize material properties and dynamics below the diffraction limit with applications to plasmonics and single molecule biophysics.
April 6
Moore’s Law and CMOS
T.P. Ma, Electrical Engineering
Since the invention of the transistor more than 5 decades ago, the tremendous progress of the electronics industry has been riding on the exponential growth of the IC technology, as characterized by the “Moore’s Law”, which basically says that the information storage capacity of a silicon chip, as well as its information processing power, doubles every 18 months. This talk will give an overview of the silicon chip technology and how we got to where we are, with a preview of what’s to come in the future. The various challenges in continued scaling of CMOS devices will be highlighted, and research opportunities will be discussed.
Sizing Up Cellular Magnetic Resonance Imaging
Eric Shapiro, Diagnostic Radiology
Cell tracking using magnetic resonance imaging is rapidly moving towards in vivo single cell detection. This has largely been facilitated by improved efficiency of contrast agent uptake, as well as optimized pulse sequences. Micron sized iron oxide particles (MPIOs) are emerging as a robust contrast agent for cell tracking. In contrast to the more commonly used nano-sized dextran coated particles, MPIOs have very high amounts of iron, as high as 90% iron and from 0.1 to 10 pg iron per particle, and are non-biodegradable, which extends the observable temporal window. Indeed, single MPIOs are detectable by MRI in cells in culture and in mouse embryos. This talk will present recent data on two projects. The first is in vivo detection of single cells in mouse livers. Primary mouse hepatocytes were labeled in culture with MPIOs and transplanted into the spleen of recipient mice. The labeled cells migrated to the liver and engrafted as single cells, which were visible by MRI. The second project is the use of MPIOs to directly label adult rat neural stem cells, in situ, and monitor the migration of the daughter neuroblasts to the olfactory bulb
March 23
Finding Fufillment in the Filling of Fullerenes
R. James Cross, Jr., Chemistry
We have devised several techniques for putting atoms and small molecules inside fullerenes. There is no chemical bond between the trapped atom and the carbon cage, yet they cannot escape without breaking several C-C bonds. So far, we have put He, Ne, Ar, Kr, Xe, CO, N2, N, and T inside C60 and higher fullerenes. NMR spectroscopy of trapped 3He and 129Xe gives a measure of the electronic structure of the carbon cage and can be used to follow chemical reactions. The trapped atom can affect the chemistry of the fullerene.
Designing Biomimetic Nanoscale Ion Transport Systems
David A. LaVan, Mechanical Engineering
The National Center for the Design of Biomimetic Nanoconductors (NCDBN) was founded to develop new technologies based on natural and synthetic ion transport devices. One project within this center is to create a synthetic in vivo power source based on the ion transport mechanism of the electric eel. The electric eel generates electricity by converting chemical energy stored in ion concentration gradients which are produced through the ATP cycle. A numerical model of electrogenic cells has been created which allows for accurate extraction of channel parameters, clarification of the mechanism of energy transduction and enables the design of electrogenic artificial cells. Using optimization methods, an artificial cell has been designed that achieved higher energy density and higher energy conversion efficiency than the natural cells. These findings are the starting point for additional studies of energy conversion in polarized cells as well as the foundation for system level design of artificial cells.
March 9
Nanoparticle Phase Transitions
Simon Mochrie, Physics
The collective behavior of nanopartlcles provides the opportunity to explore a host of key scientific questions. For example,the glass transition and protein folding remain grand challenges to both condensed matter and to nanoscience. This talk will describe recent x-ray measurements which reveal the existence of two distinct glass phases in concentrated suspensions of nanoparticles in a binary fluid. We characterize the remarkable transition from one to the other via a nanoparticle liquid phase. We will also describe recent efforts to characterize the order-disorder and mechanical behavior of a family of smart, biological nanoparticles, namely TPR repeat proteins.
Peptide-Based Catalysts for Organic Synthesis: Biomimetic Designs and Discovery Platforms
Scott J. Miller, Chemistry
Modern organic synthesis depends heavily on the use of catalysts for selective transformations. We have discovered a class of synthetic peptides that catalyze a number of selective reactions. The biomimetic design principles that led to our initial discoveries will be described. Combinatorial technique development based on the synthesis polymeric supports as vehicles for catalyst discovery will be presented. The connection between these techniques and complex, biologically active compound synthesis will be illustrated.
February 23
Nanoparticles for Drug Delivery
W. Mark Saltzman, Biomedical Engineering
Drug-loaded nanoparticles, particularly those formed from degradable polymers, have several properties that will make them useful vehicles for drug delivery including high drug loading, efficient entry into cells, and capability for selective targeting. This presentation reviews these properties, and engineering methods for achieving them with PLGA materials. The application of nanoparticles for cancer treatment, drug delivery to the brain, and delivery through epithelial cells will be reviewed.
High-Resolution Atomic Force Microscopy
Udo Schwarz, Mechanical Engineering
The world's most sensitive noncontact atomic force microscopes allow high-resolution imaging for both hard and soft materials as well as both conducting and insulating materials. They can be used to image short-range interatomic forces, resulting in “atomic resolution” images featuring single atomic defects, as well as long-range electrostatic and magnetic forces, leading to high-resolution maps of charge distributions or magnetic domains. This talk will give a short overview on the activities at Yale designed to push the resolution to its limits.
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