Engineers at the University of Pennsylvania School of Engineering and Applied Science (Penn Engineering) have used quantum sensors to develop a groundbreaking variation of nuclear quadrupolar resonance (NQR) spectroscopy, a technique traditionally employed for detecting drugs and explosives or analyzing pharmaceuticals.
An artistic representation of the minute nucleic differences detectable using the form of nuclear quadrupolar resonance described in the new paper. Image Credit: Mathieu Ouellet
Since the 1950s, radio waves have been used by scientists to identify the molecular "fingerprints" of unknown substances. This method has been instrumental in applications ranging from medical imaging via MRI machines to detecting explosives in airport security systems.
However, these approaches rely on signals averaged from vast numbers of atoms, making it impossible to observe minor variations between individual molecules. This limitation poses challenges for fields such as protein research, where even small differences in molecular shape can dictate functionality and distinguish between health and disease.
Sub-Atomic Breakthroughs
Researchers at the University of Pennsylvania School of Engineering and Applied Science (Penn Engineering) have advanced nuclear quadrupolar resonance (NQR) spectroscopy through the application of quantum sensors. Traditionally used for detecting substances like drugs and explosives or for pharmaceutical analysis, this refined technique marks a significant breakthrough.
Detailed in Nano Letters, the new approach achieves a level of precision that allows for detecting NQR signals from individual atoms, an achievement once considered unattainable. This capability is expected to transform areas such as drug development by offering insights into molecular interactions at the atomic scale.
This technique allows us to isolate individual nuclei and reveal tiny differences in what were thought to be identical molecules. By focusing on a single nucleus, we can uncover details about molecular structure and dynamics that were previously hidden. This capability allows us to study the building blocks of the natural world at an entirely new scale.
Lee Bassett, Associate Professor and Study Senior Author, Electrical and Systems Engineering, University of Pennsylvania
Discovery Born from Serendipity
The groundbreaking method originated from a surprising observation during routine experiments. Alex Breitweiser, a recent Physics Ph.D. graduate from Penn’s School of Arts & Sciences and now a researcher at IBM, noticed unexpected patterns while working with nitrogen-vacancy (NV) centers in diamonds, a common tool in quantum sensing.
Initially dismissed as experimental artifacts, the periodic signals persisted despite extensive troubleshooting. By revisiting nuclear magnetic resonance texts from the mid-20th century, Breitweiser identified a physical mechanism that accounted for the observations—a mechanism previously deemed insignificant.
Technological advancements enabled the team to detect and measure these effects, which were once beyond the capabilities of scientific instruments.
We realized we weren’t just seeing an anomaly. We were breaking into a new regime of physics that we can access with this technology.
Alex Breitweiser, Study Co-First Author and Doctoral Graduate, Physics, School of Arts & Sciences, University of Pennsylvania
Unmatched Accuracy
Collaboration with Delft University of Technology in the Netherlands further refined the understanding of the observed effects. By combining expertise in quantum sensing, experimental physics, and theoretical modeling, the team devised a method capable of isolating single atomic signals with exceptional precision.
This is a bit like isolating a single row in a huge spreadsheet. Traditional NQR produces something like an average — you get a sense of the data as a whole, but know nothing about the individual data points. With this method, it’s as though we’ve uncovered all the data behind the average, isolating the signal from one nucleus and revealing its unique properties.
Mathieu Ouellet, Doctoral Graduate and Study Other Co-First Author, University of Pennsylvania
Interpreting the Data
Deciphering the theoretical foundation behind the unexpected results was a meticulous process. Ouellet conducted extensive simulations and calculations to match the experimental data with plausible explanations.
“It’s a bit like diagnosing a patient based on symptoms. The data points to something unusual, but there are often multiple possible explanations. It took quite a while to arrive at the correct diagnosis,” said Mathieu Ouellet.
Future Potential
This new method is expected to revolutionize how scientists tackle molecular challenges. By revealing previously hidden phenomena, it offers a pathway to better understanding the molecular mechanisms shaping the natural world.
The research was conducted at the University of Pennsylvania School of Engineering and Applied Science, supported by the National Science Foundation (ECCS-1842655, DMR-2019444). Additional support came from the Natural Sciences and Engineering Research Council of Canada through a Ph.D. Fellowship awarded to Ouellet and from IBM through a Ph.D. Fellowship awarded to Breitweiser.
The study also lists contributions from co-authors Tzu-Yung Huang, a former ESE doctoral student at Penn Engineering now with Nokia Bell Labs, and Tim H. Taminiau at Delft University of Technology.
Journal Reference:
Breitweiser, A., S., et al. (2024) Quadrupolar Resonance Spectroscopy of Individual Nuclei Using a Room-Temperature Quantum Sensor. Nano Letters. doi/10.1021/acs.nanolett.4c04112