By John Oncea, Editor
Spectroscopy has played a part in several recent discoveries over the past couple of months, from discovering new, exotic states of matter to revealing the invisible. Let’s take a look at seven of these breakthroughs that are in the news.
A couple of months ago we took a look at four unique ways spectroscopy is being used, from real-time monitoring of cell cultures to its application in pharmaceutical analysis. This time let’s take a look at some of the recent breakthroughs that owe their discovery to this branch of science.
A New, Exotic State Of Matter
Physicists have discovered an exciting state of matter that appears as a well-organized crystal of subatomic particles, reports Space.com. Called a “bosonic correlated insulator,” this new state of matter could potentially unlock the door to a multitude of exotic materials made from condensed matter. The findings were published in the journal Science.
Subatomic particles can be separated into fermions and bosons and the primary differences between them are how they spin and how they interact with each other.
“Fermions, such as electrons and protons, are often thought of as the building blocks of matter because they make up atoms, and are characterized by their half-integer spin,” Space.com writes. “Two identical fermions cannot occupy the same space at the same time.
“Bosons, on the other hand, carry force — such as photons, or packets of light — and are thought to be the glue of the universe, tying together the fundamental forces of nature. These particles have whole-integer spins and multiple bosons can be in the same place at the same time.”
study lead author Chenhao Jin, a condensed-matter physicist at the University of California, Santa Barbara, said in a statement, “Bosons can occupy the same energy level; fermions don't like to stay together. Together, these behaviors construct the universe as we know it.” It is possible, however, for two fermions to transform into a boson through the formation of an exciton which occurs when a negatively charged electron combines with a positively charged hole in another fermion.
“To see how excitons interact with one another, the researchers layered a lattice of tungsten disulfide atop a similar lattice of tungsten diselenide in an overlapping pattern called a moiré,” writes Space.com. “Then, they shined a strong beam of light through the lattices — a method known as ‘pump-probe spectroscopy.’ These conditions pushed the excitons together until they were so densely packed that they could no longer move, creating a new symmetrical crystalline state with a neutral charge — a bosonic-correlated insulator.
This is the first time, then, that a new state of matter has been successfully created in an actual matter system, rather than in synthetic systems. This breakthrough enables scientists to gain fresh insights into the behavior of bosons. Additionally, the techniques employed by the research team to uncover this new state of matter hold the potential to facilitate the development of other types of bosonic materials.
Detect And Confirm The Most Distant Know Galaxies? ✓
In late 2022, a group of astronomers used information collected by the James Webb Space Telescope (JWST) to confirm the existence of galaxies that are the earliest and most distant ever observed, according to Science Daily. The light from these galaxies was emitted more than 13.4 billion years ago, which means that they are from a time when the universe was only 2% of its current age, less than 400 million years after the Big Bang.
“We've discovered galaxies at fantastically early times in the distant universe,” said Brant Robertson, professor of astronomy and astrophysics at UC Santa Cruz. “With JWST, for the first time, we can now find such distant galaxies and then confirm spectroscopically that they really are that far away.”
Astronomers determine the distance to a galaxy by analyzing its redshift. Due to the expansion of the universe, distant objects appear to be moving away from us, causing their light to stretch to longer, redder wavelengths. While photometric techniques can estimate redshifts by analyzing images captured through different filters, spectroscopy is needed to accurately measure them by separating the light into its component wavelengths.
Recent research has focused on four galaxies with redshifts higher than 10. Two galaxies initially observed by Hubble have confirmed redshifts of 10.38 and 11.58. The other two galaxies, detected in JWST images, are the most distant galaxies confirmed by spectroscopy to date, with redshifts of 13.20 and 12.63. A redshift of 13.2 corresponds to roughly 13.5 billion years ago.
“These are well beyond what we could have imagined finding before JWST,” Robertson said. “At Redshift 13, the universe is only about 325 million years old.”
Revealing The Invisible With THz Spectroscopy
Scientists from the University of Ottawa (aller Gee-Gees!) and the Max Planck Institute for the Science of Light are proposing a breakthrough approach that will facilitate discoveries in materials science by combining terahertz (THz) spectroscopy and real-time monitoring.
According to a University of Ottawa, a team led by Jean-Michel Ménard, associate professor of physics at the University’s Faculty of Science, used chirped-pulse encoding and photonic time-stretch to allow for them to use terahertz waves to record real-time movies of hot electrons in silicon at 50,000 frames per second — faster than ever before.
To capture low-energy dynamics of a material, two techniques are employed. The first one involves imprinting THz pulse information onto a chirped supercontinuum, creating a rainbow-like effect in the optical region. The second technique involves stretching the rainbow pulse in time using a long fiber, which slows down the information rate for recording in real-time by advanced electronic equipment. This process is repeated using a train of pulses at 20-microsecond intervals, which can be combined to create a movie of the material's dynamics.
“In this study, we present a novel photonics system that can measure in real-time the low-energy dynamics of complex physical phenomena with a time resolution approaching the microsecond. Our setup is distinctive: it is a compact system that replaces a technology that was only accessible in large synchrotron facilities and can quickly perform time-resolved THz spectroscopy, a powerful technique to analyze various materials,” said Ménard.
Experiments relying on this system will trace vibrational resonances of molecules to study the enigmatic role of enzymes in chemical reactions and observe invisible changes in living organisms when they’re exposed to a sudden rise in temperature.
“In condensed matter experiments, our rapid THz photonic system will be used to observe a range of non-reversible electronic or lattice reconfigurations, notably occurring during phase transitions,” says Ménard. “We anticipate that (this) will play a crucial role in revealing a new range of fast and non-reproducible processes rendering THz spectroscopy an even more efficient characterization tool to make impactful discoveries in materials physics.”
SICS Enables Precise DNA ID
Researchers at the Ecole Polytechnique Fédérale de Lausanne (EPFL) have developed a new nanopore approach for manipulating individual molecules such as DNA that allows unprecedented control and precision according to The Science Advisory Board. This newly-developed approach – called scanning ion conductance spectroscopy (SICS) – “can be used to determine DNA's sequence of nucleotides, which encode genetic information, by analyzing how each molecule perturbs an ionic current as it passes through a nanopore in a membrane.”
SICS uses a glass nanopore mounted on a nanopositioner to spatially select molecules that slow the molecule's transit through the nanopore, allowing thousands of consecutive readings to be taken of the same molecule, as well as of different locations on the molecule. “By controlling the distance between the nanopore and glass surface, we can actively select the region of interest on the molecule and scan it a controlled number of times and at a controlled velocity,” the researchers said.
SICS could be used with molecules other than DNA, including peptides, with potential applications in proteomics as well as biomedical and clinical research. “Finding a solution for sequencing peptides has been a significant challenge due to the complexity of their ‘license plates,’ said team leader Aleksandra Radenovic, head of the Laboratory of Nanoscale Biology in the School of Engineering. “For me, the most exciting hope is that this new control might open an easier path ahead to peptide sequencing.”
Spectroscopy + Machine Learning = Rapid Molybdenum Ore Grade Detection
Spectroscopy Online writes that researchers from Northeastern University in China developed a novel method for rapidly detecting the grade of molybdenum ore using a combination of visible-infrared spectroscopy and machine learning. The approach combines visible-infrared spectroscopy and machine learning to achieve rapid and accurate molybdenum ore grade detection.
The team conducted a study on 128 molybdenum ore samples, using visible-infrared spectroscopy to collect spectral data. They used partial least squares analysis to extract 13 latent variables from 973 spectral features. To determine the nonlinear relationship between the spectral signal and molybdenum content, they employed the Durbin-Watson test and runs test to analyze the partial residual plots.
The researchers realized that the complex behavior of spectral data required nonlinear modeling, prompting them to adopt Extreme Learning Machine (ELM) as an alternative to linear modeling methods. To optimize ELM parameters effectively, they devised a unique approach known as the Golden Jackal Optimization of adaptive T-distribution (MTSVD-TGJO-ELM). Furthermore, to tackle ill-posed problems related to ELM, they integrated a modified truncated singular value decomposition.
“The integration of visible-infrared spectroscopy and machine learning techniques holds significant potential for enhancing the efficiency of ore grade determination,” writes Spectroscopy Online. “With its ability to assess molybdenum ore grade swiftly and accurately, the proposed method paves the way for improved beneficiation processes, ultimately leading to higher ore recovery rates. This research marks a significant advancement in the field and showcases the power of innovative approaches in resource extraction and utilization.”
Single Atom Spectra
The American Physical Society (APS) reports that a technique that combines X-ray spectroscopy with scanning tunneling microscopy has delivered X-ray spectra of single atoms. The discovery was made by a team led by Saw-Wai Hla of Ohio University and Argonne National Laboratory in Illinois which, for the first time, measured the X-ray spectra of single atoms. The breakthrough was achieved with a technique that combines X-ray spectroscopy with the premier single-atom-resolving technique – scanning tunneling microscopy (STM).
“For years, Hla and his team have worked to combine the best of both worlds – STM’s atomic resolution and X-ray spectroscopy’s chemical sensitivity,” writes APS. “Their approach makes use of a previously demonstrated technique called synchrotron X-ray STM (SX-STM). In the technique, a sample is scanned by an STM tip while being exposed to the X-ray beam delivered by a synchrotron. The tip records a large tunneling current when the X-ray energy is resonant with core-level transitions in the sample’s atoms. By measuring the current as the X-ray energy is varied, researchers can recover an X-ray absorption spectrum of the sample below the tip.”
According to Hla, his team is currently focused on enhancing the setup even further. The researchers intend to conduct measurements utilizing polarized X-rays, which would increase the experiment's sensitivity to a single atom's spin state. This would be particularly useful for examining rare-earth-based materials that have promising uses in spintronics and magnetic memory technology.
Raman Spectroscopy And Cancer Cell Typing
The potential of Raman spectroscopy in recognizing the expression of the nucleophosmin (NPM1) mutant gene in leukemia cells was the subject of a study conducted by lead authors Yihui Wu and Mingbo Chi from the Chinese Academy of Sciences in Changchun, China reports Spectroscopy Online.
“Raman spectroscopy is a technique that could be useful in cancer diagnosis applications and biomedical research,” Spectroscopy Online writes. “This study explores its applicability in detecting the spectral characteristics of acute myeloid leukemia (AML) cells with and without the NPM1 mutation. Their study provides insights into the underlying reasons for the observed spectral differences through transcriptomic analysis.”
The researchers experimented by analyzing the Raman spectra of two AML cell lines, THP-1 and HL-60, that did not have the NPM1 mutation and the OCI-AML3 cell line that had the NPM1 mutant gene. They found that there were distinct differences in the intensity of multiple peaks, which corresponded to molecules such as chondroitin sulfate (CS), nucleic acid, and protein, among others, between the average Raman spectra of the mutated and nonmutated cells. To further comprehend these variations, the researchers conducted a quantitative analysis of gene expression data from both types of cells. They identified differentially expressed genes and analyzed their roles in regulating CS proteoglycan and protein synthesis. Interestingly, the researchers discovered that the differences observed in the single-cell Raman spectral information aligned with the differences in transcriptional profiles.
According to Spectroscopy Online, “These findings highlight the potential of Raman spectroscopy as a valuable tool for cancer cell typing, specifically in recognizing the expression of the NPM1 mutant gene in leukemia cells. By providing detailed molecular information without the need for labeling or sample destruction, Raman spectroscopy offers a promising avenue for further advancements in cancer research and diagnosis.”