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Berkeley Lab Researchers Observe Shortest Wavelength Plasmons Ever in Single Walled Nanotubes•
by Kate Greene
For years, scientists have had an itch they couldn’t scratch. Even with the best microscopes and spectrometers, it’s been difficult to study and identify molecules at the so-called mesoscale, a region of matter that ranges from 10 to 1000 nanometers in size. Now, with the help of broadband infrared light from the Advanced Light Source (ALS) synchrotron at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), researchers have developed a broadband imaging technique that looks inside this realm with unprecedented sensitivity and range.
The new technique, called Synchrotron Infrared Nano-Spectroscopy or SINS, will enable in-depth study of complex molecular systems, including liquid batteries, living cells, novel electronic materials and stardust.
“The big thing is that we’re getting full broadband infrared spectroscopy at 100 to 1000 times smaller scale,” says Hans Bechtel, principal scientific engineering associate at Berkeley Lab. “This is not an incremental achievement. It’s really revolutionary.”
In a Proceedings of the National Academy of Sciences paper published May 6 online, titled “Ultra-broadband infrared nano-spectroscopic imaging,” Berkeley Lab’s Bechtel and Michael Martin, a Berkeley Lab staff scientist, and colleagues from Markus Raschke’s group at the University of Colorado at Boulder describe SINS. They demonstrate the nanoscope’s ability to capture broadband spectroscopic data over a variety of samples, including a semiconductor-insulator system, a mollusk shell, proteins, and a peptoid nanosheet. Martin says these demonstrations just “scratch the surface” of the potential of the new technique.
SINS combines two pre-existing infrared technologies: a newer technique called infrared scattering-scanning near-field optical microscopy (IR s-SNOM) and an old laboratory standby, known even to college chemistry students, called Fourier Transform Infrared Spectroscopy (FTIR). A clever melding of these two tools, combined with the intense infrared light of the synchrotron at Berkeley Lab gives the researchers the ability to identify clusters of molecules sized as small as 20 to 40 nanometers.
The new approach overcomes long-standing barriers with pre-existing microscopy techniques that often involve demanding technical and sample preparation requirements. Infrared spectroscopy uses low-energy light, is minimally invasive, and is applicable under ambient conditions, making it an excellent tool for chemical and molecular identifications in systems that are static as well as those that are living and dynamic. The technique works by shining low-energy infrared light onto a molecular sample. Molecules can be thought of as systems of balls (atoms) and springs (bonds between atoms) that vibrate with characteristic wiggles; they absorb infrared radiation at frequencies that correspond to their natural vibrating modes. The output from this absorption is a spectrum, often called a fingerprint, which shows distinctive peaks and dips, depending on the bonds and atoms present in the sample.
But infrared spectroscopy has its challenges too. While it works well for bulk samples, traditional infrared spectroscopy can’t resolve molecular composition below about 2000 nanometers. The major hurdle is the diffraction limit of light, which is the fundamental barrier that determines the smallest focus spot of light and is particularly troublesome for the large wavelengths of infrared light. In recent years, though, the diffraction limit has been overcome by a technique called scattering-scanning near-field optical microscopy, or s-SNOM, which involves shining light onto a metallic tip. The tip acts as an antenna for the light, directing it to a tiny region at its apex just tens of nanometers wide.
This trick is what’s used in IR s-SNOM, where infrared light is coupled to a metallic tip. The challenge with IR s-SNOM, however, is that researchers have been relying on infrared light produced by lasers. Lasers emit a large number of photons needed for the technique, but because they operate in a narrow wavelength band, they can only probe a narrow range of molecular vibrations. In other words, laser light simply can’t give you the flexibility to explore a spectrum of mixed molecules.
Bechtel, Martin and Raschke’s team saw the opportunity to use Berkeley Lab’s ALS to overcome the laser limitation. The lab’s synchrotron produces broadband infrared light with a high-photon count that can be focused to the diffraction limit. The researchers coupled the synchrotron light to a metallic tip with an apex of about 20 nanometers, focusing the infrared beam onto the samples. The resulting spectrum is analyzed with a modified FTIR instrument.
“This is actually one of very few examples where synchrotron light has been coupled to scanning probe microscopy,” says Raschke. “Moreover, the implementation of the technique at the synchrotron brings chemical nano-spectroscopy and -imaging out of the lab of a few laser science experts and makes it available for a broader scientific community at a user facility.”
From mollusks to moon rocks
The team demonstrated the technique by confirming the spectroscopic signature of silicon dioxide on silicon and by illustrating the sharp chemical transition that occurs within the shells of the blue mussel (M. edulis). Additionally, the researchers looked at proteins and a peptoid nanosheet, an engineered, ultra-thin film of proteins with medical and pharmacological applications.
Martin is excited for the potential of SINS, which is available for researchers from any institution to use. In particular he’s interested in a closer look at battery systems, with the hope that understanding battery chemistry on the mesoscale could provide insight into better performance. Further out, he expects SINS to be useful for a range of biochemistry as well. “This hints at a dream I’ve had in my mind, to look at the surface of a cell, inside the bi-layer membrane, the channels, and receptors,” says Martin. “If we could put a SINS tip on a living cell, we could watch biochemistry happen in real time.”
Bechtel, for his part, is intrigued by the possibility of using SINS for the study of lunar rocks, meteorites and stardust. These extraterrestrial materials have a molecular diversity that is difficult to resolve on the nanoscale, particularly in a non-destructive manner for these rare samples. A better understanding of the makeup of moon rocks and dust from space could provide clues to the formation of the planets and solar system.
Raschke is using the technique to study the processes that limit the performance of organic solar cells. He is looking to further improve the flexibility of the technique such that it can be applied under variable and controlled atmospheric and low-temperature conditions. Among other tweaks, he plans to increase the sensitivity of the technique with the ultimate goal of performing singe-molecule chemical spectroscopy.
This research was supported by the DOE Office of Science.
Infrared Technique at Berkeley Lab’s Advanced Light Source Could Help Improve Flow Reactor Chemistry for Pharmaceuticals and Other Products
A pathway to more effective and efficient synthesis of pharmaceutical drugs and other flow reactor chemical products has been opened by a study in which for the first time the catalytic reactivity inside a microreactor was mapped in high resolution from start-to-finish. The results not only provided a better understanding of the chemistry behind the catalytic reactions, they also revealed opportunities for optimization, which resulted in better catalytic performances. The study was conducted by a team of scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley.
Working at Berkeley Lab’s Advanced Light Source (ALS), the team used tightly focused beams of infrared and x-ray light to track the evolution of a catalytic reaction with a spatial resolution of 15 microns. This research was led by chemists Dean Toste and Gabor Somorjai, both of whom hold joint appointments with Berkeley Lab and UC Berkeley. Somorjai is also a member of the Kavli Energy NanoSciences Institute at Berkeley.
“The formation of different chemical products during the reactions was analyzed using in situ infrared micro-spectroscopy, while the state of the catalyst along the flow reactor was determined using in situ x-ray absorption microspectroscopy,” says Toste, a faculty scientist with Berkeley Lab’s Chemical Sciences Division. “Our results show that using infrared microspectroscopy to monitor the evolution of reactants into a desired product could be an invaluable tool for optimizing pharmaceutical-related synthetic processes that take place in flow reactors.”
Toste and Somorjai are the corresponding authors of a paper in the Journal of the American Chemical Society (JACS) titled “In-situ IR and X-ray high spatial-resolution microspectroscopy measurements of multistep organic transformation in flow microreactor catalyzed by Au nanoclusters.” Elad Gross, a post-doctoral scholar with the corresponding authors, is the lead author. Other co-authors are Xing-Zhong Shu, Selim Alayoglu, Hans Bechtel and Michael Martin.
Catalysts – substances that speed up the rates of chemical reactions without themselves being chemically changed – are used to initiate virtually every manufacturing process that involves chemistry. There are two basic modes of catalytic reactors – batch, in which a final chemical product is produced over a series of separate stages; and flow, in which chemical reactions run in a continuously flowing stream to yield a final product. With the implementation of microreactors, the pharmaceutical industry aims to make the switch from batch mode to flow mode, as flow reactors provide a highly recyclable, scalable and efficient setup that enhances the sustainability and performance of catalysts. However, the synthesis of pharmaceutical drugs is a multiphase, complex process that needs to be carefully monitored. Until now, there has been no capability to follow the multistep production process of pharmaceutical drugs in flow reactors without perturbing the flow reaction.
“Our method allows us to watch an entire catalytic movie, from reactants into products formation, instead of only snapshots of the catalytic process,” says Gross. “In most cases before, chemists had to extrapolate information on the reaction process based on analysis of the final product. With our technique, we don’t have to guess what happened in the first scene based on what we saw in the final scene, since now we’re able to directly watch a high-resolution movie of the entire process.”
For this study, Gross and his colleagues used a heterogeneous catalyst of gold nanoclusters loaded onto a silica support to produce dihydropyran, an organic compound whose formation involves multiple reactant steps. Each of these reactants shows a distinguishable infrared signature, allowing their evolution into the final product to be precisely monitored with an infrared beam. The infrared microspectroscopy was performed at ALS beamline 1.4.
“ALS beamline 1.4 provides a bright infrared beam with a diameter of less than 10 micrometers,” Gross says. “The small diameter of the beam enabled us to draw a map of the flow reactor with high spatial resolution of up to 15 micrometers. Without this high resolution imaging, we would not be able to track and understand key processes in the catalytic reaction.”
In following the reaction kinetics step-by-step, the Berkeley researchers discovered that the catalytic reaction they were observing is completed within the first five-percent of the flow reactor’s volume, which meant that the remaining 95-percent of the reactor, though packed with catalyst did not contribute to the catalytic process.
“Based on this result, we were able to minimize the volume of the flow reactor and the amount of catalyst by an order of magnitude without deteriorating the catalytic reactivity,” Gross says.
While the infrared microspectroscopy technique employed in this study allowed one-dimensional mapping of a catalytic reaction along the path of the flow reactor, the actual flow reactor is three-dimensional. Gross and Toste along with Michael Martin and Hans Bechtel, beam-scientists at the ALS infrared beamline, are now exploring techniques that would permit two- and three-dimensional mapping of catalytic reactions.
“Multidimensional imaging will give us the ability to know where exactly inside the volume of the flow reactor the catalytic reaction takes place,” Gross says. “This will provide us advanced tools for better understanding and optimization of the catalytic reaction.”
This research was supported by the DOE Office of Science.
For more about the research of Dean Toste go here
For more about the research of Gabor Somorjai go here
3D IR Images Now in Full Color
Berkeley Lab and University of Wisconsin Researchers Unveil FTIR spectro-microtomography
An iconic moment in the history of Hollywood movie magic was born in the 1939 film The Wizard of Oz when Judy Garland as Dorothy Gale stepped out of the black and white world of Kansas into the rainbow colored world of Oz. An iconic moment in the history of infrared imaging may have been born with the announcement of the first technique to offer full color IR tomography.
A collaboration between researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of Wisconsin-Milwaukee (UWM) has combined Fourier Transform Infrared (FTIR) spectroscopy with computed tomography (CT-scans) to create a non-destructive 3D imaging technique that provides molecular-level chemical information of unprecedented detail on biological and other specimens with no need to stain or alter the specimen.
“The notion of having the colors in a 3D reconstructed image being tied to real chemistry is powerful,” says Michael Martin, an infrared imaging expert at Berkeley Lab’s Advanced Light Source, a DOE national user facility. “We’ve all seen pretty 3D renderings of medical scans with colors, for example bone-colored bones, but that’s simply an artistic choice. Now we can spectrally identify the specific types of minerals within a piece of bone and assign a color to each type within the 3D reconstructed image.”
Martin is one of two corresponding authors of a paper describing this research in the journal Nature Methods titled “3D Spectral Imaging with Synchrotron Fourier Transform Infrared Spectro-microtomography.” The other corresponding author is UWM physicist Carol Hirschmugl, Director of the Laboratory for Dynamics and Structure at Surfaces and a principal investigator with UW-Madison’s Synchrotron Radiation Center (SRC).
Every individual type of molecule absorbs infrared (IR) light at specific wavelengths that are as characteristic as a human fingerprint. IR spectroscopy can be used to identify the chemical constituents of a sample and the application of the Fourier-transform algorithm allows all IR fingerprints to be simultaneously recorded. FTIR spectroscopy is especially valuable for imaging proteins and other biological samples because it is non-destructive and can be performed without altering the sample. Martin and Hirschmugl and their colleagues have combined FTIR with computed tomography, the technique for reconstructing 3D images out of multiple cross-sectional slices, to achieve what is believed to be the first demonstration of FTIR spectro-microtomography.
“FTIR spectro-microtomography involves low-energy IR photons that do not affect living systems and do not require artificial labels, contrast agents or sectioning,” Hirschmugl says. “It greatly enhances the capabilities of both FTIR spectroscopy and CT by creating a full-color spectro-microtomogram in which each voxel contains a complete spectrum (millions of spectra per sample) that provides a wealth of information for advanced spectral segregation techniques such as clustering, neural networks and principal-component analysis.”
The success of FTIR spectro-microtomography was enabled by the speed with which 2D FTIR images can be obtained at the SRC’s Infrared Environmental Imaging (IRENI) beamline. The SRC is a synchrotron radiation facility that provides infrared, ultra violet, and soft X-ray light for scientific research. IRENI offers one the nation’s highest performance IR imaging beamlines through the use of unique focal plane array detectors.
“With capabilities such as those at IRENI, we can obtain hundreds of 2D spectral images as a sample is rotated,” Martin says. “For each wavelength, we can then reconstruct a full 3D representation of the sample via computed tomography algorithms.”
Martin, Hirschmugl and their colleagues developed a motorized sample mount that precisely rotates the sample while holding it at the focus of an IR microscope. Data collection of 2D spectral transmission images as a function of sample angle is automated, and the computed tomography algorithms allow full reconstructions for every wavelength measured that are then reassembled into a complete spectrum for every voxel.
“We’ve been able to do a lot of exciting science with 2D FTIR imaging at the diffraction limit using synchrotron infrared beamlines, and it’s very exciting to now be able to expand this to true 3D spectroscopic imaging,” Martin says. “While the most immediate applications will be in biomedical imaging, I think full color FTIR spectro-microtomography will also be applicable to imaging 3D structures in biofuels, plants, rocks, algae, soils, agriculture and possibly even studies of art history where different layers of paints could be revealed.”
The Berkeley Lab and UWM researchers have already successfully applied FTIR spectro-microtomography to obtain 3D images of the molecular architecture of the cell walls in a flowering plant – zinnia – and in a woody plant – poplar. A better understanding of the chemical composition and architecture of plant cell walls is critical to the ultimate success of making biofuels from plant biomass. The collaboration also applied FTIR spectro-microtomography to study human hair, which has a distinctive biochemical construction, and an intact grouping of pluripotent mouse stem cells.
“The hair study showed that spectral reconstructions can be done on larger fully hydrated biological samples and that we can spectrally identify a fully buried portion of the sample,” Hirschmugl says. “The mouse study shows that our technique has promise not only for stem cell screening without the use of dyes or probes, but also for promoting a better understanding of the biochemical structure of differentiating stem cells in their microenvironment.”
The collaborators are continuing to improve the efficiency by which they can collect and analyze FTIR spectro-microtomography with new advances being incorporated at IRENI and at IR beamline 5.4 of Berkeley Lab’s Advanced Light Source (ALS), a project being overseen by Martin. The work at the ALS is being done in collaboration with Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).
Other co-authors of the Nature Methods paper are Charlotte Dabat-Blondeau, Miriam Unger, Julia Sedlmair, Dilworth Parkinson, Hans Bechtel, Barbara Illman, Jonathan Castro, Marco Keiluweit, David Buschke, Brenda Ogle and Michael Nasse.
This research was funded by the DOE Office of Science and the National Science Foundation. Berkeley Lab’s ALS and NERSC are funded by the DOE Office of Science.
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