University of Pennsylvania engineers have developed a method to detect signals from individual atoms, achieving a level of precision previously thought impossible. The advance could aid in understanding protein folding and developing new drugs by revealing molecular structures at an unprecedented scale.
The new technique, detailed in Nano Letters, refines a decades-old method called nuclear quadrupolar resonance (NQR) spectroscopy, commonly used to detect explosives and analyze pharmaceuticals. While traditional methods average signals from trillions of atoms, this approach can isolate and measure individual atomic signals.
“This technique allows us to isolate individual nuclei and reveal tiny differences in what were thought to be identical molecules,” says Lee Bassett, Associate Professor in Electrical and Systems Engineering and director of Penn’s Quantum Engineering Laboratory. “By focusing on a single nucleus, we can uncover details about molecular structure and dynamics that were previously hidden.”
The discovery emerged from an unexpected observation during routine experiments with quantum sensors in diamonds. Alex Breitweiser, then a doctoral student and now at IBM, noticed unusual patterns in the data that persisted despite extensive testing. By consulting physics textbooks from the 1950s and ’60s, he identified a previously dismissed physical mechanism that explained their observations.
“We realized we weren’t just seeing an anomaly,” Breitweiser explains. “We were breaking into a new regime of physics that we can access with this technology.”
Mathieu Ouellet, a recent doctoral graduate and co-first author, compares the achievement to data analysis: “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.”
The path to understanding the results was complex. “It’s a bit like diagnosing a patient based on symptoms,” Ouellet notes. “The data points to something unusual, but there are often multiple possible explanations. It took quite a while to arrive at the correct diagnosis.”
The research involved collaboration with Delft University of Technology in the Netherlands, combining expertise in experimental physics, quantum sensing, and theoretical modeling. The work was supported by the National Science Foundation, with additional funding from the Natural Sciences and Engineering Research Council of Canada and IBM.
This advancement builds on technology that has been fundamental to scientific research since the 1950s, when scientists first began using radio waves to identify molecular structures. The increased precision could lead to better understanding of protein folding and molecular interactions critical to drug development and disease research.