Tuesday, July 12, 2011

NMR/MRI applied to microfluidic chromatography

By pairing an award-winning remote-detection version of NMR/MRI technology with a unique version of chromatography specifically designed for microfluidic chips, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have opened the door to a portable system for highly sensitive multi-dimensional chemical analysis that would be impractical if not impossible with conventional technologies.

Alexander Pines, a faculty senior scientist in Berkeley Lab's Materials Sciences Division and the Glenn T. Seaborg Professor of Chemistry at the University of California (UC) Berkeley, is one of the word's foremost authorities on NMR (nuclear magnetic resonance) and its daughter technology, MRI (Magnetic Resonance Imaging). In this latest development, he led a collaboration in which a remote detection NMR/MRI technique that can rapidly identify the chemical constituents of samples in microfluidic "lab-on-a-chip" devices was used to perform analyses in a microscale monolithic chromatograph column.

"We have presented the first demonstration that a monolithic chromatograph column can be used to separate small molecules on a timescale that is compatible with NMR/MRI detection, an important first step to portable chromatographic devices," says Vikram Bajaj, a project scientist in the Pines' group who is the corresponding author of a paper describing this work in the journal Analytical Chemistry.

The Analytical Chemistry paper is titled "Remotely Detected NMR for the Characterization of Flow and Fast Chromatographic Separations Using Organic Polymer Monoliths." Co-authoring the paper with Pines and Bajaj were Thomas Teisseyre, Jiri Urban†, Nicholas Halpern-Manners, Stuart Chambers and Frantisek Svec.

Chromatography is one of the indispensable tools of chemistry. By dissolving sample into a fluid -- called the "mobile phase" -- and flushing it through a solid medium -- called the "stationary phase" -- chemists can separate the sample's constituent chemical species -- called analytes -- for identification and measurement, as well as for purification purposes. Analytes will be separated on the basis of how fast each individual species diffuses through the stationary phase.

"The coupling of our remote NMR/MRI technology with monolithic chromatography columns in a microfluidic chip enables us to obtain high resolution, velocity-encoded images of a mobile phase flowing through the stationary phase," Bajaj says. "Our technique provides both real-time peak detection and chemical shift information for small aromatic molecules, and demonstrates the unique power of magnetic resonance, both direct and remote, in studying chromatographic processes."

The coupling of remote NMR/MRI to chromatography was made possible by the polymer monolithic column, a technology developed by Analytical Chemistry paper co-author Frantisek Svec, a chemist who directs the Organic and Macromolecular Synthesis facility at Berkeley Lab's Molecular Foundry, a DOE nanoscience center. In conventional chromatography, the stationary phase column is typically filled with porous polymer beads or some other discrete medium whose physical or chemical properties modulate the diffusion rates of analytes passing through. In Svec's stationary phase, a chromatography column is filled with a monolithic solid polymer -- meaning it is a single, continuous piece -- that is perforated throughout with nanoscopic pores.

"Polymer monoliths as a separation media can be compared to a single large particle that does not contain inter-particular voids," Svec says. "As a result, all the mobile phase must pass through the stationary phase as convective flow rather than diffusion during chromatographic processes. This convective flow greatly accelerates the rate of analyte separation."

The remote NMR/MRI technology whose development was led by Pines won a 2011 R&D 100 Award. These awards, known as the "Oscars of Innovation," recognize the year's 100 most significant proven technological advances. Through a combination of remote instrumentation, JPEG-style image compression algorithms and other key enhancements, this remote NMR/MRI technology can zoom in on microscopic objects of interest within a sample flowing through the columns of a microfluidic chip with unprecedented spatial and time resolutions.

"Our remote NMR/MRI technology enables time-resolved imaging of multi-channel flow, dispenses with the need for large and expensive magnets for analysis, allows us to analyze complex and unprocessed mixtures in one pass, and adds portability to NMR/MRI," Bajaj says.

The key to the success of remote NMR/MRI technology is the decoupling of the NMR/MRI signal encoding and detection phases. NMR/MRI signals arise from a property found in the atomic nuclei of almost all molecules called "spin," which makes the nuclei act as if they were bar magnets with poles that point either "north" or "south." Obtaining an NMR/MRI signal from a sample depends upon an excess of nuclear spins pointing in one direction or the other. In a conventional NMR/MRI set-up, in which the signal encoding and detection phases take place within one machine, this require the presence of a powerful external magnetic field. The remote NMR/MRI technology developed by Pines and his group, in which NMR?MRI signal encoding and detection are carried out independently, can detect NMR/MRI signals without the need of such a strong magnet, yet it still provides the same outstanding sensitivity of conventional NMR/MRI.

"With our remote NMR/MRI technology and the polymer monoliths of Frank Svec's group, we were able to look inside optically opaque microfluidic columns and measure the velocity of the flowing fluid during a chromatographic separation," Bajaj says. "We were also able to demonstrate in-line monitoring of chromatographic separations of small molecules at high flow rates."

Results using the remote NMR/MRI technique with the polymer monoliths showed a much better ability to discriminate between different analytes at the molecular level, Bajaj says, than comparable analysis using spectrometry based on either mass or optical properties. This paves the way for multidimensional analysis, in which the result of a chromatographic separation would be encoded into an NMR/MRI signal by charge, size or some other factor and stored. The encoded fluid would then be run through a second separation and those results would also be encoded into an NRM/MRI signal and stored.

"This would allow us to create a multidimensional chromatography experiment that does not require the fluid volume to be physically partitioned," Bajaj says. "The fluid would, quite literally, be partitioned in the magnetic degrees of freedom instead."

This research was funded by the DOE Office of Science.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Thomas Z. Teisseyre, Jiri Urban, Nicholas W. Halpern-Manners, Stuart D. Chambers, Vikram S. Bajaj, Frantisek Svec, Alexander Pines. Remotely Detected NMR for the Characterization of Flow and Fast Chromatographic Separations Using Organic Polymer Monoliths. Analytical Chemistry, 2011; : 110701140950082 DOI: 10.1021/ac2010108

Researchers build an antenna for light

 University of Toronto researchers have derived inspiration from the photosynthetic apparatus in plants to engineer a new generation of nanomaterials that control and direct the energy absorbed from light.

Their findings are reported in the journal Nature Nanotechnology.

The U of T researchers, led by Professors Shana Kelley and Ted Sargent, report the construction of what they term "artificial molecules."

"Nanotechnologists have for many years been captivated by quantum dots -- particles of semiconductor that can absorb and emit light efficiently, and at custom-chosen wavelengths," explained co-author Kelley, a Professor at the Leslie Dan Faculty of Pharmacy, the Department of Biochemistry in the Faculty of Medicine, and the Department of Chemistry in the Faculty of Arts & Science. "What the community has lacked -- until now -- is a strategy to build higher-order structures, or complexes, out of multiple different types of quantum dots. This discovery fills that gap."

The team combined its expertise in DNA and in semiconductors to invent a generalized strategy to bind certain classes of nanoparticles to one another.

"The credit for this remarkable result actually goes to DNA: its high degree of specificity -- its willingness to bind only to a complementary sequence -- enabled us to build rationally-engineered, designer structures out of nanomaterials," said Sargent, a Professor in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto, who is also the Canada Research Chair in Nanotechnology. "The amazing thing is that our antennas built themselves -- we coated different classes of nanoparticles with selected sequences of DNA, combined the different families in one beaker, and nature took its course. The result is a beautiful new set of self-assembled materials with exciting properties."

Traditional antennas increase the amount of an electromagnetic wave -- such as a radio frequency -- that is absorbed, and then funnel that energy to a circuit. The U of T nanoantennas instead increased the amount of light that is absorbed and funneled it to a single site within their molecule-like complexes. This concept is already used in nature in light harvesting antennas, constituents of leaves that make photosynthesis efficient. "Like the antennas in radios and mobile phones, our complexes captured dispersed energy and concentrated it to a desired location. Like the light harvesting antennas in the leaves of a tree, our complexes do so using wavelengths found in sunlight," explained Sargent.

"Professors Kelley and Sargent have invented a novel class of materials with entirely new properties. Their insight and innovative research demonstrates why the University of Toronto leads in the field of nanotechnology," said Professor Henry Mann, Dean of the Leslie Dan Faculty of Pharmacy.

"This is a terrific piece of work that demonstrates our growing ability to assemble precise structures, to tailor their properties, and to build in the capability to control these properties using external stimuli," noted Paul S. Weiss, Fred Kavli Chair in NanoSystems Sciences at UCLA and Director of the California NanoSystems Institute.

Kelley explained that the concept published in the Nature Nanotechnology paper is a broad one that goes beyond light antennas alone.

"What this work shows is that our capacity to manipulate materials at the nanoscale is limited only by human imagination. If semiconductor quantum dots are artificial atoms, then we have rationally synthesized artificial molecules from these versatile building blocks."

Also contributing to the paper were researchers Sjoerd Hoogland and Armin Fischer of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering, and Grigory Tikhomirov and P. E. Lee of the Leslie Dan Faculty of Pharmacy.

The publication was based in part on work supported by the Ontario Research Fund Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Research Chairs program and the National Institutes of Health (NIH).

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Toronto Faculty of Applied Science & Engineering, via EurekAlert!, a service of AAAS.

Journal Reference:

Grigory Tikhomirov, Sjoerd Hoogland, P. E. Lee, Armin Fischer, Edward H. Sargent, Shana O. Kelley. DNA-based programming of quantum dot valency, self-assembly and luminescence. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.100

Red light from carbon nanotubes

To the human eye, carbon nanotubes usually appear as a black powder. They can hardly be forced to emit light, as they are excellent electrical conductors and capture the energy from other luminescent chemical species placed nearby. The researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw contributed recently to the development of a relatively simple method allowing the nanotubes exposed to UV to emit red light.

The researchers involved in the international FINELUMEN project, coordinated by Dr. Nicola Armaroli from Italy's Istituto per la Sintesi Organica e la Fotoreattivita, Consiglio Nazionale delle Ricerche (CNR-ISOF) in Bolonia, have developed an efficient method to fabricate a new photonic material: carbon nanotubes coated with chemicals that are capable of displaying red light. "We take part at the project as a research group specializing in studies on lanthanide compounds. We decided to combine their high luminescent properties with excellent mechanical and electrical characteristics of nanotubes," says Prof. Marek Pietraszkiewicz from Warsaw's Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS).

Carbon nanotubes can be envisaged as a graphite sheet rolled-up into a seamless cylinder. The surface area of each nanotube is relatively high and allows to attach many other molecules, including those capable to emit light. "Attachment of light-emitting complexes directly to the nanotube is, however, not favourable, because the latter, as a black absorber, would highly quench the luminescence," explains Valentina Utochnikova, a PhD student at the IPC PAS. To reduce undesired effect of light absorption, the nanotubes are first subject to a thermal reaction at temperature 140-160 oC in a solution of ionic liquid modified with a terminal azido function. The reaction yields nanotubes coated with molecules acting as anchors-links. On one side the anchors are attached to the surface of the nanotube, and on the other they can attach molecules capable of displaying visible light. The free terminal of each link bears a positive charge.

So prepared nanotubes are subsequently transferred into another solution containing a negatively charged lanthanide complex -- tetrakis-(4,4,4-trifluoro-1-(2-naphtyl-1,3-butanedionato)europium. "Lanthanide compounds contain elements from the VI group of the periodic table and are very attractive for photonics, as they are characterised by a high luminescence quantum yield and a high colour purity of the emitted light," stresses Utochnikova.

After dissolving in solution, negatively charged europium complexes are spontaneously caught by positively charged free terminals of anchors attached to nanotubes due to electrostatic interaction. As a result, each nanotube is durably coated with molecules capable to emit visible light. Upon completion of the reaction, the modified nanotubes are washed and dried. The final product is a sooty powder. If the powder is, however, exposed to UV irradiation, the lanthanide complexes anchored to nanotubes start immediately to emit red light.

The concept of how to modify the nanotubes and the reagents -- ionic liquid and lanthanide complex for carbon nanotube coating -- has been developed in Prof. Pietraszkiewicz's research group at the IPC PAS, whereas the modification of nanotubes and spectral studies have been performed by research groups from the University of Namur, Belgium, and CNR-ISOF from Bolonia, Italy. It is essential that chemical reactions leading to fabrication of new light-emitting nanotubes turned out to be significantly simpler than those used so far.

The photonic material received can be used, among others, to detect molecules including those of biological importance. The identification would then take place by analysing of how the luminescence of nanotubes changes upon deposition of molecules under study thereon. Good charge conductivity combined with high luminescence properties make new nanotubes an attractive material also for OLED-based technologies.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

Laser, electric fields combined for new 'lab-on-chip' technologies

Researchers are developing new technologies that combine a laser and electric fields to manipulate fluids and tiny particles such as bacteria, viruses and DNA for a range of potential applications, from drug manufacturing to food safety.

The technologies could bring innovative sensors and analytical devices for "lab-on-a-chip" applications, or miniature instruments that perform measurements normally requiring large laboratory equipment, said Steven T. Wereley, a Purdue University professor of mechanical engineering.

The method, called "hybrid optoelectric manipulation in microfluidics," is a potential new tool for applications including medical diagnostics, testing food and water, crime-scene forensics, and pharmaceutical manufacturing.

"This is a cutting-edge technology that has developed over the last decade from research at a handful of universities," said Aloke Kumar, a Wigner Fellow and staff member at Oak Ridge National Laboratory.

He is lead author of an article about the technology featured on the cover of the July 7 issue of Lab on a Chip magazine, published by the Royal Society of Chemistry.

The article is written by Wereley; Kumar; Stuart J. Williams, an assistant professor of mechanical engineering at the University of Louisville; Han-Sheng Chuang, an assistant professor in the Department of Biomedical Engineering at National Cheng Kung University; and Nicolas G. Green, a researcher at the University of Southampton.

"A very important aspect is that we have achieved an integration of technologies that enables manipulation across a very wide length scale spectrum," Kumar said. "This enables us to manipulate not only big-sized objects like droplets but also tiny DNA molecules inside droplets by using one combined technique. This can greatly enhance efficiency of lab-on-a-chip sensors."

Kumar, Williams and Chuang are past Purdue doctoral students who worked with Wereley. Much of the research has been based at the Birck Nanotechnology Center at Purdue's Discovery Park.

The technologies are ready for some applications, including medical diagnostics and environmental samples, Williams said.

"There are two main thrusts in applications," he said. "The first is micro- and nanomanufacturing and the second is lab-on-a-chip sensors. The latter has demonstrated biologically relevant applications in the past couple of years, and its expansion in this field is immediate and ongoing."

The technology works by first using a red laser to position a droplet on a platform specially fabricated at Purdue. Next, a highly focused infrared laser is used to heat the droplets, and then electric fields cause the heated liquid to circulate in a "microfluidic vortex." This vortex is used to isolate specific types of particles in the circulating liquid, like a micro centrifuge. Particle concentrations replicate the size, location and shape of the infrared laser pattern.

"This works very fast," Wereley said. "It takes less than a second for particles to respond and get pulled out of solution."

Systems using the hybrid optoelectric approach can be designed to precisely detect, manipulate and screen certain types of bacteria, including particular strains that render heavy metals less toxic.

"We are shooting for biological applications, such as groundwater remediation," Wereley said. "Even within the same strain of bacteria some are good at the task and some are not, and this technology makes it possible to efficiently cull those bacteria from others. The bacteria could be injected into the contaminated ground. You seed the ground with the bacteria, but first you need to find an economical way to separate it."

Purdue researchers also are pursuing the technology for pharmaceutical manufacturing, he said.

"These types of technology are good at being very dynamic, which means you can decide in real time to grab all particles of one size or one type and put them somewhere," Wereley said. "This is important for the field of pharmacy because a number of drugs are manufactured from solid particles suspended in liquid. The particles have to be collected and separated from the liquid."

This process is now done using filters and centrifuges.

"A centrifuge does the same sort of thing but it's global, it creates a force on every particle, whereas this new technology can specifically isolate only certain particles," Wereley said. "We can, say, collect all the particles that are one micron in diameter or get rid of anything bigger than two microns, so you can dynamically select which particles you want to keep."

The technology also may be used as a tool for nanomanufacturing because it shows promise for the assembly of suspended particles, called colloids. The ability to construct objects with colloids makes it possible to create structures with particular mechanical and thermal characteristics to manufacture electronic devices and tiny mechanical parts. The nanomanufacturing applications are at least five years away, he said.

The technology also can be used to learn fundamental electrokinetic forces of molecules and biological structures, which is difficult to do with existing technologies.

"Thus there are very fundamental science applications of these technologies as well," Kumar said.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Purdue University. The original article was written by Emil Venere.

Journal Reference:

Aloke Kumar, Stuart J. Williams, Han-Sheng Chuang, Nicolas G. Green, Steven T. Wereley. Hybrid opto-electric manipulation in microfluidics—opportunities and challenges. Lab on a Chip, 2011; 11 (13): 2135 DOI: 10.1039/C1LC20208A

Researchers clarify properties of 'confined' water within single-walled carbon nanotube pores

Water and ice may not be among the first things that come to mind when you think about single-walled carbon nanotubes (SWCNTs), but a Japan-based research team hoping to get a clearer understanding of the phase behavior of confined water in the cylindrical pores of carbon nanotubes zeroed in on confined water's properties and made some surprising discoveries.

The team, from Tokyo Metropolitan University, Nagoya University, Japan Science and Technology Agency, and National Institute of Advanced Industrial Science and Technology, describes their findings in the American Institute of Physics' Journal of Chemical Physics.

Although carbon nanotubes consist of hydrophobic (water repelling) graphene sheets, experimental studies on SWCNTs show that water can indeed be confined in open-ended carbon nanotubes.

This discovery gives us a deeper understanding of the properties of nanoconfined water within the pores of SWCNTs, which is a key to the future of nanoscience. It's anticipated that nanoconfined water within carbon nanotubes can open the door to the development of a variety of nifty new nanothings—nanofiltration systems, molecular nanovalves, molecular water pumps, nanoscale power cells, and even nanoscale ferroelectric devices.

"When materials are confined at the atomic scale they exhibit unusual properties not otherwise observed, due to the so-called 'nanoconfinement effect.' In geology, for example, nanoconfined water provides the driving force for frost heaves in soil, and also for the swelling of clay minerals," explains Yutaka Maniwa, a professor in the Department of Physics at Tokyo Metropolitan University. "We experimentally studied this type of effect for water using SWCNTs."

Water within SWCNTs in the range of 1.68 to 2.40 nanometers undergoes a wet-dry type of transition when temperature is decreased. And the team discovered that when SWCNTs are extremely narrow, the water inside forms tubule ices that are quite different from any bulk ices known so far. Strikingly, their melting point rises as the SWCNT diameter decreases—contrary to that of bulk water inside a large-diameter capillary. In fact, tubule ice occurred even at room temperature inside SWCNTs.

"We extended our studies to the larger diameter SWCNTs up to 2.40 nanometers and successfully proposed a global phase behavior of water," says Maniwa. "This phase diagram (See Figure) covers a crossover from microscopic to macroscopic regions. In the macroscopic region, a novel wet-dry transition was newly explored at low temperature."

Results such as these contribute to a greater understanding of fundamental science because nanoconfined water exists and plays a vital role everywhere on Earth—including our bodies. "Understanding the nanoconfined effect on the properties of materials is also crucial to develop new devices, such as proton-conducting membranes and nanofiltration," Maniwa notes.

Next up, the team plans to investigate the physical properties of confined water discovered so far inside SWCNTs (such as dielectricity and proton conduction). They will pursue this to obtain a better understanding of the molecular structure and transport properties in biological systems.


Extremely rapid water: Scientists decipher a protein-bound water chain

Researchers from the RUB-Department of Biophysics of Prof. Dr. Klaus Gerwert have succeeded in providing evidence that a protein is capable of creating a water molecule chain for a few milliseconds for the directed proton transfer. The combination of vibrational spectroscopy and biomolecular simulations enabled the elucidation of the proton pump mechanism of a cell-membrane protein in atomic detail. The researchers demonstrated that protein-bound water molecules play a decisive role in the function.

Their results were selected for the Early Edition of Proceedings of the National Academy of Sciences.

Protein-bound water is decisive

Specific proteins can transport protons from one side (uptake side) of the cell membrane to the other side (release side). This is a central process in biological energy conversion. In past editions of Nature and Angewandte Chemie the researchers from the Department of Biophysics had already published their observations that in the ground state the protein-bound water molecules at the release side are optimally arranged for the release of protons. "As with dominos, the protein initiates movement of the protons which finally leads to their release," explains Prof. Gerwert. Just how the protein re-attains its initial state in order to start another pumping cycle remained to be clarified. New protons must be acquired at the uptake side of the protein to substitute the released protons. The researchers in Bochum discovered that a chain of only three water molecules is formed for just a few thousandths of a second to transfer the protons into the interior of the protein.

Water molecules lead the way

The protein kills two birds with one stone. The water molecules are disordered during the release phase, which prevents the protons from being transported in the false direction. Only during the uptake phase, they are correctly aligned and can conduct protons. These results are the solution to the riddle as to why proton transfer only functions in one direction at the uptake side and why the protein is capable of effective and directional pumping. "This paper, together with the two preceding publications, now constitutes a trilogy which supplies a full explanation for the proton pumping cycle at an atomic level," summarizes Prof. Gerwert.

Experimental physics and theoretical chemistry combined

The researchers combined experimental physics with theoretical chemistry to be able to observe the processes with a high spatial and temporal resolution at a nano-level. Steffen Wolf simulated the structural changes within the protein using biomolecular computer simulations (molecular dynamics simulations). Erik Freier subsequently verified the effects experimentally using a special kind of vibrational spectroscopy developed by Prof. Gerwert (time-resolved step-scan FTIR spectroscopy). "This interdisciplinary interplay, which showed that the individual components of the protein are as precisely synchronized as the gears of a machine, was the key to success," says Prof. Gerwert.

As in water, so in the protein

The protein arranges the three water molecules so skillfully that they transport the protons using the physico-chemical Grotthuss mechanism. In the 1950s, the Nobel Prize winner Manfred Eigen elucidated this mechanism to explain extremely rapid, non-directional proton transport in water. Surprisingly enough, the publications of the RUB researchers now reveal that amino acids coupled with protein-bound water molecules can give this extremely rapid transportation a direction of movement. Prof. Gerwert's team was thus able to augment Manfred Eigen's results and apply them to protein research.

Effective conversion of light energy into chemical energy

The group of research scientists in Bochum primarily works with the membrane protein bacteriorhodopsin, which is used by certain bacteria to carry out an archaic form of photosynthesis. Bacteriorhodopsin creates a proton concentration gradient by transporting protons from the interior to the exterior of a cell. Other proteins use this gradient to produce ATP, the universal cellular fuel. It is important that the proton transport has a specific direction and that spontaneous backflow of protons is prevented to ensure that light energy can be effectively used.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Ruhr-Universitaet-Bochum, via AlphaGalileo.

Journal Reference:

E. Freier, S. Wolf, K. Gerwert. Proton transfer via a transient linear water-molecule chain in a membrane protein. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1104735108