Waterloo physicists kept molecular sensor spins coherent for about 400 microseconds, roughly 60 times longer than a standard comparison technique.Mechanical readout detected weak magnetic fields and small groups of nuclear spins, offering a route toward molecular-scale sensing.The experiment used about 140 sensor molecules under cryogenic conditions; imaging an individual protein remains a future goal.<\/p>\n
A single molecule, suspended at the edge of detectability, could soon help scientists map the structure of life itself. Researchers at the Institute for Quantum Computing at the University of Waterloo<\/a> have introduced a new sensing method that moves science closer to that goal. Their work shows how a single molecule can act as a quantum sensor, opening a new path for studying proteins and other biomolecules at the smallest scales.<\/p>\n A New Way To See The Invisible<\/p>\n Understanding how molecules behave has long challenged scientists. Proteins, for example, fold into complex shapes that control how they function. These shapes influence everything from cell growth to disease. Yet many current imaging tools require large samples, making it difficult to capture the behavior of a single molecule.<\/p>\n The new approach changes that. Instead of relying on bulk measurements, the research team designed a sensor based on a single molecule. This sensor can detect tiny magnetic signals<\/a> from nearby atoms, offering a way to study structures one molecule at a time.<\/p>\n Dr. Raffi Budakian, a professor at the University of Waterloo and a lead researcher on the project, described the breakthrough. \u201cOur experiment establishes a new paradigm in nanoscale quantum sensing,\u201d he said. \u201cThere are other milestones to reach before we have a sensor sensitive to single molecules, but we know how to get there, and this is a huge demonstration.\u201d<\/p>\n Waterloo researchers develop new quantum-sensing technique that could map single protein structures and lead to breakthroughs in medicine. (CREDIT: University of Waterloo) Turning Molecules Into Sensors<\/p>\n Quantum sensors rely on a property called spin. Each atom behaves like a tiny magnet, producing a faint magnetic field. When atoms sit close together, their fields interact. These interactions carry information about distance and structure.<\/p>\n In this study, the team used a special molecule called trityl-OX063. This molecule contains an electron<\/a> whose spin can be controlled and measured. Because the spin remains stable for long periods, it can act as a precise probe of its surroundings.<\/p>\n The researchers placed this molecule near other atoms and tracked how its spin changed over time. Nearby nuclear spins altered the behavior of the sensor. By measuring these changes, the team could detect the magnetic environment at an extremely small scale.<\/p>\n Unlike traditional sensors, this system does not rely on rigid materials. Instead, it uses a flexible molecular platform that can be positioned close to the target. This proximity improves sensitivity and allows measurements that were previously out of reach.<\/p>\n Measuring With Mechanical Precision<\/p>\n To read out the signal, the team used a tiny mechanical device. A silicon nanowire<\/a>, about 100 nanometers wide and 20 microns long, acted as a sensitive probe. This structure moves slightly in response to magnetic forces.<\/p>\n The researchers used a class of molecules called trityl-OX063 as the quantum sensor. Its spin is isolated and protected, preserving its quantum properties. (CREDIT: University of Waterloo) <\/p>\n When the molecular sensor interacts with nearby spins, it creates a small force. The nanowire detects this force with high precision. This method, known as mechanical detection, allows researchers to measure signals that would otherwise be too weak to observe.<\/p>\n \u201cUsing force detection in quantum sensing is new and opens up a whole new avenue of approaches,\u201d Budakian said. \u201cIt brings us closer to mapping single protein structures<\/a>.\u201d<\/p>\n The ability to combine molecular sensing with mechanical readout marks a key shift. It offers a different route compared to light-based techniques, which often require complex setups and limit how close the sensor can get to the target.<\/p>\n Extending The Life Of Quantum States<\/p>\n One of the biggest challenges in quantum sensing is keeping the system stable long enough to collect useful data. Quantum states tend to decay quickly due to interactions with the environment. This process, known as decoherence, limits measurement accuracy.<\/p>\n The research team addressed this problem by developing a new control method. This technique helps preserve the sensor\u2019s quantum state for a longer time. As a result, the sensor can gather more detailed information before losing coherence.<\/p>\n Sahand Tabatabaei, a PhD candidate and first author of the study, explained the improvement. \u201cThe new control sequence we developed extended the coherence time to 400 microseconds, so it maintained its quantum state<\/a> roughly 60 times longer than what is achieved with standard spin-echo techniques in the same system.\u201d<\/p>\n Sahand Tabatabaei and Pritam Priyadarsi, both PhD candidates, stand next to a low temperature scanning force microscope, the instrument that was used for taking experiment measurements. (CREDIT: University of Waterloo) <\/p>\n This increase in coherence time allows the sensor to detect weaker signals. It also improves the precision of measurements, bringing the system closer to the goal of single-molecule detection.<\/p>\n Moving Beyond Traditional Techniques<\/p>\n For years, scientists have relied on diamond-based quantum sensors. These systems use tiny defects in synthetic diamonds<\/a> to measure magnetic fields. While effective, they come with limitations. The sensors are fixed within a solid structure, making it difficult to position them close to certain targets.<\/p>\n The new molecular approach offers greater flexibility. Because the sensor is itself a molecule, it can be placed directly near the system being studied. This reduces the distance between sensor and target, which is critical for detecting weak signals.<\/p>\n The method also avoids some of the complexity associated with light-based detection. Instead, it uses mechanical motion to read out information. This simplifies the setup and opens new possibilities for sensor design.<\/p>\n The researchers demonstrated that their system can already detect the magnetic state of about 10 spins. While this is not yet at the level of a single atom, it represents a significant step forward.<\/p>\n SQUINT sensing platform. (CREDIT: Physical Review X) Toward Mapping Protein Structures<\/p>\n The ability to detect small groups of spins has important implications. Proteins and other biomolecules<\/a> are made up of atoms arranged in specific patterns. By measuring the magnetic interactions between these atoms, scientists can infer the structure of the molecule.<\/p>\n Current imaging methods often average signals over many molecules. This can hide important details about individual behavior. A single-molecule sensor could reveal variations that are otherwise lost.<\/p>\n The new technique offers a path toward that goal. By improving sensitivity and control, researchers hope to eventually map the structure of a single protein. This would provide deeper insight into how biological systems function.<\/p>\n Such knowledge could transform fields like drug discovery. Understanding the exact shape of a protein helps scientists design treatments that interact more effectively with it.<\/p>\n A Step Toward The Future<\/p>\n The study represents an early but important step. The researchers have shown that molecular spins<\/a> can act as reliable quantum sensors. They have also demonstrated a new way to read out signals using mechanical detection.<\/p>\n Challenges remain. The system must become more sensitive and more stable before it can study individual molecules routinely. However, the path forward is clearer than before.<\/p>\n XYXYd sequence design and simulation. (CREDIT: Physical Review X) <\/p>\n Budakian noted the progress. \u201cWe\u2019re not too far away now because of this advancement,\u201d he said.<\/p>\n The work highlights how advances in quantum technology continue to reshape scientific tools. By combining chemistry, physics, and engineering, researchers are building systems that can probe the smallest structures in nature.<\/p>\n Dig deeper into molecular spins and nanoscale sensing<\/p>\n These resources explore quantum-sensing principles, molecular probes and earlier magnetic measurements of biological structures.<\/p>\n