Atoms in a nanocrystal cooperate, much like in biomolecules


atomsinanano
Nanocrystals of cadmium selenide, known for their brilliant luminescence, display intriguing chemical behavior resulting from positive cooperation between atoms, a behavior akin to that found in biomolecules. Credit: Prashant Jain        

(Phys.org) —Researchers have long thought that biological molecules and synthetic nanocrystals were similar only in size. Now, University of Illinois at Urbana-Champaign chemists have found that they can add reactivity to the list of shared traits. Atoms in a nanocrystal can cooperate with each other to facilitate binding or switching, a phenomenon widely found in biological molecules.

The finding could catalyze manufacturing of for smart sensors, solar cells, tiny transistors for optical computers, and medical imaging. Led by chemistry professor Prashant Jain, the team published its findings in the journal Nature Communications.

“In geological, industrial and domestic environments, the nanoscale grains of any material undergo chemical transitions when they are put under reactive conditions,” Jain said. “Iron rusting over time and diamond forming from carbon are examples of two commonly occurring transitions. Understanding how these transitions occur on the scale of the tiniest grains of the material is a major motivation of our work.”

Scientists can exploit such transitions to make nanocrystals that conform to a particular structure. They can make a nanocrystal of one material and transform it into another material, essentially using the original nanocrystal framework as a template for creating a nanocrystal of the new material with the same size and shape. This lets researchers create nanocrystals of new materials in shapes and structures they may not be able to otherwise.

In the new study, the researchers transformed tiny crystals of the material cadmium selenide to crystals of copper selenide. Copper selenide nanocrystals have a number of interesting properties that can be used for solar energy harvesting, optical computing and laser surgery. Transformation from cadmium selenide creates nanocrystals with a purity difficult to attain from other methods.

The researchers, including graduate student Sarah White, used advanced microscopy and spectroscopy techniques to determine the dynamics of the atoms within the crystals during the transformation and found that the transformation occurs not as a slow diffusion process, but as a rapid switching thanks to co-operativity.

The researchers saw that once the cadmium-selenide nanocrystal has taken up a few initial copper “seed” impurities, atoms in the rest of the lattice can cooperate to rapidly swap out the rest of the cadmium for copper. Jain compares the crystals to hemoglobin, the molecule in red blood cells that carries oxygen. Once one oxygen molecule has bound to hemoglobin, other binding sites within hemoglobin slightly change conformation to more easily pick up more oxygen. He posits that similarly, copper impurities might cause a structural change in the nanocrystal, making it easier for more copper ions to infiltrate the nanocrystal in a rapid cascade.

The researchers reproduced the experiment with silver, in addition to copper, and saw similar, though slightly less speedy, cooperative behavior.

Now, Jain’s team is using its advanced imaging to watch transitions happen in single nanocrystals, in real time.

“We have a sophisticated optical microscope in our lab, which has now allowed us to catch a single nanocrystal in the act of making a transition,” Jain said. “This is allowing us to learn hidden details about how the transition actually proceeds. We are also learning how one nanocrystal behaves differently from another.”

Next, the researchers plan to explore biomolecule-like cooperative phenomena in other solid-state materials and processes. For example, co-operativity in catalytic processes could have major implications for or manufacturing of expensive specialty chemicals.

“In the long term, we are interested in exploiting the co-operative behavior to design artificial smart materials that respond in a switch-like manner like hemoglobin in our body does,” Jain said.

Explore further:     Researchers extend galvanic replacement reactions to metal oxide nanocrystals

More information: “Co-operativity in a nanocrystalline solid-state transition.” Sarah L. White, Jeremy G. Smith, Mayank Behl, Prashant K. Jain. Nature Communications 4, Article number: 2933 DOI: 10.1038/ncomms3933

Read more at: http://phys.org/news/2013-12-atoms-nanocrystal-cooperate-biomolecules.html#jCp

Read more at: http://phys.org/news/2013-12-atoms-nanocrystal-cooperate-biomolecules.html#jCp

Tiny ‘Lego’ blocks Build Janus nanotubes: For NEW drugs and water purification


Nanotubes images(Nanowerk News) Researchers have created tiny protein  tubes named after the Roman god Janus which may offer a new way to accurately  channel drugs into the body’s cells.
Using a process which they liken to molecular Lego, scientists  from the University of Warwick and the University of Sydney have created what  they have named ‘Janus nanotubes’ – very small tubes with two distinct faces.  The study is published in the journal Nature Communications (“Janus cyclic peptide–polymer nanotubes”).
They are named after the Roman god Janus who is usually depicted  as having two faces, since he looks to the future and the past.
The Janus nanotubes have a tubular structure based on the  stacking of cyclic peptides, which provide a tube with a channel of around 1nm –  the right size to allow small molecules and ions to pass through.
Attached to each of the cyclic peptides are two different types  of polymers, which tend to de-mix and form a shell for the tube with two faces –  hence the name Janus nanotubes.
The faces provide two remarkable properties – in the solid  state, they could be used to make solid state membranes which can act as  molecular ‘sieves’ to separate liquids and gases one molecule at a time. This  property is promising for applications such as water purification, water  desalination and gas storage.
In a solution, they assemble in lipids bilayers, the structure  that forms the membrane of cells, and they organise themselves to form pores  which allow the passage of molecules of precise sizes. In this state they could  be used for the development of new drug systems, by controlling the transport of  small molecules or ions inside cells.
Sebastien Perrier of the University of Warwick said: “There is  an extraordinary amount of activity inside the body to move the right chemicals  in the right amounts both into and out of cells.
“Much of this work is done by channel proteins, for example in  our nervous system where they modulate electrical signals by gating the flow of  ions across the cell membrane.
“As ion channels are a key component of a wide variety of  biological process, for example in cardiac, skeletal and muscle contraction,  T-cell activation and pancreatic beta-cell insulin release, they are a frequent  target in the search for new drugs.
“Our work has created a new type of material – nanotubes – which  can be used to replace these channel processes and can be controlled with a much  higher level of accuracy than natural channel proteins.
“Through a process of molecular engineering – a bit like  molecular Lego – we have assembled the nanotubes from two types of building  blocks – cyclic peptides and polymers.
“Janus nanotubes are a versatile platform for the design of  exciting materials which have a wide range of application, from membranes – for  instance for the purification of water, to therapeutic uses, for the development  of new drug systems.”
Source: University of Warwick
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Self-steering particles go with the flow


Asymmetrical particles could make lab-on-a-chip diagnostic devices more efficient and portable.

Anne Trafton, MIT News Office

stretchy-electronics-4MIT chemical engineers have designed tiny particles that can “steer” themselves along preprogrammed trajectories and align themselves to flow through the center of a microchannel, making it possible to control the particles’ flow through microfluidic devices without applying any external forces.

 

self aligning nano 20131108111613-0

A slightly asymmetrical particle flows along the center of a microfluidic channel

Such particles could make it more feasible to design lab-on-a-chip devices, which hold potential as portable diagnostic devices for cancer and other diseases. These devices consist of microfluidic channels engraved on tiny chips, but current versions usually require a great deal of extra instrumentation attached to the chip, limiting their portability.

Much of that extra instrumentation is needed to keep the particles flowing single file through the center of the channel, where they can be analyzed. This can be done by applying a magnetic or electric field, or by flowing two streams of liquid along the outer edges of the channel, forcing the particles to stay in the center.

The new MIT approach, described in Nature Communications, requires no external forces and takes advantage of hydrodynamic principles that can be exploited simply by altering the shapes of the particles.

Lead authors of the paper are Burak Eral, an MIT postdoc, and William Uspal, who recently received a PhD in physics from MIT. Patrick Doyle, the Singapore Research Professor of Chemical Engineering at MIT, is the senior author of the paper.

Exploiting asymmetry

The work builds on previous research showing that when a particle is confined in a narrow channel, it has strong hydrodynamic interactions with both the confining walls and any neighboring particles. These interactions, which originate from how particles perturb the surrounding fluid, are powerful enough that they can be used to control the particles’ trajectory as they flow through the channel.

The MIT researchers realized that they could manipulate these interactions by altering the particles’ symmetry. Each of their particles is shaped like a dumbbell, but with a different-size disc at each end.

When these asymmetrical particles flow through a narrow channel, the larger disc encounters more resistance, or drag, forcing the particle to rotate until the larger disc is lagging behind. The asymmetrical particles stay in this slanted orientation as they flow.

Because of this slanted orientation, the particles not only move forward, in the direction of the flow, they also drift toward one side of the channel. As a particle approaches the wall, the perturbation it creates in the fluid is reflected back by the wall, just as waves in a pool reflect from its wall. This reflection forces the particle to flip its orientation and move toward the center of the channel.

Slightly asymmetrical particles will overshoot the center and move toward the other wall, then come back toward the center again until they gradually achieve a straight path. Very asymmetrical particles will approach the center without crossing it, but very slowly. But with just the right amount of asymmetry, a particle will move directly to the centerline in the shortest possible time.

“Now that we understand how the asymmetry plays a role, we can tune it to what we want. If you want to focus particles in a given position, you can achieve that by a fundamental understanding of these hydrodynamic interactions,” Eral says.

“The paper convincingly shown that shape matters, and swarms can be redirected provided that shapes are well designed,” says Patrick Tabeling, a professor at the École Supérieure de Physique et de Chimie Industrielles in Paris, who was not part of the research team. “The new and quite sophisticated mechanism … may open new routes for manipulating particles and cells in an elegant manner.”

Diagnosis by particles

In 2006, Doyle’s lab developed a way to create huge batches of identical particles made of hydrogel, a spongy polymer. To create these particles, each thinner than a human hair, the researchers shine ultraviolet light through a mask onto a stream of flowing building blocks, or oligomers. Wherever the light strikes, solid polymeric particles are formed in the shape of the mask, in a process called photopolymerization.

During this process, the researchers can also load a fluorescent probe such as an antibody at one end of the dumbbell. The other end is stamped with a barcode — a pattern of dots that reveals the particle’s target molecule.

This type of particle can be useful for diagnosing cancer and other diseases, following customization to detect proteins or DNA sequences in blood samples that can be signs of disease. Using a cytometer, scientists can read the fluorescent signal as the particles flow by in single file.

“Self-steering particles could lead to simplified flow scanners for point-of-care devices, and also provide a new toolkit from which one can develop other novel bioassays,” Doyle says.

The research was funded by the National Science Foundation, Novartis, and the Institute for Collaborative Biotechnologies through the U.S. Army Research Office.

Graphene has potential as cell membrane modelling surface


lipid-nanoparticleResearchers at Manchester University have demonstrated that membranes can be  directly ‘written’ on to a graphene surface using Lipid Dip-Pen Nanolithography  (L-DPN).

The researchers at Manchester University – led by Dr Aravind Vijayaraghavan,  and Dr Michael Hirtz at the Karlsruhe Institute of Technology (KIT) – describe  their work in Nature Communications.

The human body contains 100 trillion cells, each of which is enveloped in a  cell membrane that have a plethora of proteins, ion channels and other molecules  embedded in them, each performing vital functions.

Understand these systems will enable their application in areas such as  bio-sensing, bio-catalysis and drug-delivery. Considering that it is difficult  to accomplish this by studying live cells inside the human body, scientists have  developed model cell membranes on surfaces outside the body, to study the  systems and processes under more convenient and accessible conditions.

Dr Vijayaraghavan’s team at Manchester and their collaborators at KIT have  shown that graphene is a suitable new surface on which to assemble these model  membranes, and is claimed to bring many advantages compared to existing  surfaces.

In a statement, Dr Vijayaraghavan said: ‘Firstly, the lipids spread uniformly  on graphene to form high-quality membranes. Graphene has unique electronic  properties; it is a semi-metal with tuneable conductivity.

‘When the lipids contain binding sites such as the enzyme called biotin, we  show that it actively binds with a protein called streptavidin. Also, when we  use charged lipids, there is charge transfer from the lipids into graphene which  changes the doping level in graphene. All of these together can be exploited to  produce new types of graphene/lipids based bio-sensors.’

Dr. Michael Hirtz (KIT) said: ‘The [L-DPN] technique utilises a very sharp  tip with an apex in the range of several nanometres as a means to write lipid  membranes onto surfaces in a way similar to what a quill pen does with ink on  paper.

‘The small size of the tip and the precision machine controlling it allows of  course for much smaller patterns, smaller than cells, and even right down to the  nanoscale.

‘By employing arrays of these tips multiple different mixtures of lipids can  be written in parallel, allowing for sub-cellular sized patterns with diverse  chemical composition.’

 

Read more:  http://www.theengineer.co.uk/medical-and-healthcare/news/graphene-has-potential-as-cell-membrane-modelling-surface/1017291.article#ixzz2hhu6QkMK

Faster Computing, Smaller Memory Devices and Lower Power Consumption: Memory Breakthrough


Memory breakthrough could bring faster computing, smaller memory devices and  lower power consumption

how-nanotechnology-could-change-solar-panels-photovoltaic_66790_600x450(Nanowerk News) Memory devices like disk drives, flash  drives and RAM play an important role in our lives. They are an essential  component of our computers, phones, electronic appliances and cars. Yet current  memory devices have significant drawbacks: dynamic RAM memory has to be  refreshed periodically, static RAM data is lost when the power is off, flash  memory lacks speed, and all existing memory technologies are challenged when it  comes to miniaturization.
Increasingly, memory devices are a bottleneck limiting  performance. In order to achieve a substantial improvement in computation speed,  scientists are racing to develop smaller and denser memory devices that operate  with high speed and low power consumption.
Prof. Yossi Paltiel and research student Oren Ben-Dor at the  Hebrew University of Jerusalem’s Harvey M. Krueger Family Center for Nanoscience and  Nanotechnology, together with researchers from the Weizmann Institute of  Science, have developed a simple magnetization progress that, by eliminating the  need for permanent magnets in memory devices, opens the door to many  technological applications.
Published in Nature Communications, the research paper,  A chiral-based magnetic memory device without a  permanent magnet, was written by Prof. Yossi Paltiel, Oren Ben Dor and Shira  Yochelis at the Department of Applied Physics, Harvey M. Krueger Family Center  for Nanoscience and Nanotechnology, Hebrew University of Jerusalem; and Shinto  P. Mathew and Ron Naaman at the Department of Chemical Physics, Weizmann  Institute of Science.
The research deals with the flow properties of electron charge  carriers in memory devices. According to quantum mechanics, in addition to their  electrical charge, electrons also have a degree of internal freedom called spin,  which gives them their magnetic properties. The new technique, called magnetless  spin memory (MSM), drives a current through chiral material (a kind of  abundantly available organic molecule) and selectively transfers electrons to  magnetize nano magnetic layers or nano particles. With this technique, the  researchers showed it is possible to create a magnetic-based memory device that  does not require a permanent magnet, and which could allow for the  miniaturization of memory bits down to a single nanoparticle.
The potential benefits of magnetless spin memory are many. The  technology has the potential to overcome the limitations of other magnetic-based  memory technologies, and could make it possible to create inexpensive,  high-density universal memory-on-chip devices that require much less power than  existing technologies. Compatible with integrated circuit manufacturing  techniques, it could allow for inexpensive, high density universal  memory-on-chip production.
According to the Hebrew University’s Prof. Paltiel, “Now that  proof-of-concept devices have been designed and tested, magnetless spin memory  has the potential to become the basis of a whole new generation of faster,  smaller and less expensive memory technologies.”
The technology transfer companies of the Hebrew University  (Yissum) and the Weizmann Institute of Science (Yeda) are working to promote the  realization of this technology, by licensing its use and raising funds for  further development and commercialization. With many possible applications, it  has already attracted the attention of start-up funds.
The Hebrew University’s Center of Nanoscience and Nanotechnology  helped with device fabrication and advice. Prof. Paltiel acknowledges the  Yessumit internal grant from the Hebrew University, and Ron Naaman and Shinto P.  Mathew acknowledge the support of the Minerva Foundation.
Source: Hebrew University of Jerusalem

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Photoluminescent SiC tetrapods


qdot-imagescaf658qe-4.jpgAndrew P. Magyar, Igor Aharonovich, Mor Baram, Evelyn L. Hu

(Submitted on 29 Nov 2012)

Photoluminescent SiC tetrapods

Abstract: Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors which allow control over their geometry via simple chemical processes. Here, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow linewidth photoluminescence at wavelengths spanning the visible to near infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This new, previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics and optoelectronics.

Comments: 14 pages, 4 figures
Subjects: Materials Science (cond-mat.mtrl-sci)
Cite as: arXiv:1211.6801 [cond-mat.mtrl-sci]
(or arXiv:1211.6801v1 [cond-mat.mtrl-sci] for this version)

Submission history

From: Andrew Magyar [view email] [v1] Thu, 29 Nov 2012 02:50:49 GMT  (1877kb,D)