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Identifying an unknown chemical or biological substance usually requires sophisticated laboratory equipment, creating a problem when the material is discovered in the field. Samples may need to be collected, transported and analyzed before personnel know what they are dealing with, or what level of protection they need.
Researchers at Johns Hopkins Applied Physics Laboratory (APL) are exploring whether quantum sensing could shrink that process into a device roughly the size of a laptop.
The technology is based on nuclear magnetic resonance (NMR) spectroscopy, a laboratory technique used to identify substances by examining their molecular structure. Conventional NMR systems apply strong magnetic fields to atomic nuclei and measure the signals produced as their spins respond.
Those signals can reveal detailed information about a molecule, but the equipment required is typically large. Traditional systems can depend on superconducting magnets, cryogenic cooling and relatively substantial samples, making them impractical for soldiers or emergency personnel to carry.
The approach replaces much of that infrastructure with quantum sensors based on nitrogen-vacancy (NV) centers in diamond.
According to Interesting Engineering, an NV center is a tiny defect in a diamond’s atomic structure, created when a nitrogen atom replaces a carbon atom beside a vacant position. These defects are extremely sensitive to surrounding magnetic fields.
When illuminated by a green laser, the center emits red light. Researchers can analyze that light to determine its quantum spin state and, from there, detect the weak magnetic signatures produced by nearby atomic nuclei.
The approach could potentially analyze samples containing only tens or hundreds of atoms, dramatically reducing the amount of material needed.
Sensitivity remains the central challenge. The nuclear spins near the diamond surface must remain detectable long enough to produce useful information. To address this, researchers have proposed microscopic “nano-containers” fabricated directly onto the diamond, physically confining samples near the sensor.
Simulations suggest one proposed geometry could improve NMR sensitivity and accuracy by roughly an order of magnitude. The team is now working to manufacture the structures and determine whether laboratory experiments match those predictions.
A proof-of-concept sensor already measures magnetic fields through NV-center spin states, but it has not yet demonstrated a field-ready ability to identify chemical or biological threats.
If successful, the technology could give military personnel a portable tool for assessing suspicious substances near the point of discovery. Rather than reproducing every capability of a laboratory, it could help answer more immediate questions: Is this substance dangerous, what might it be, and what protection is required?
Potential applications also extend to environmental monitoring, GPS-denied navigation and low-frequency communications.
For now, the key task is improving nanoscale NMR sensitivity. If that works, a chemical-analysis technique normally associated with room-sized laboratory equipment could eventually become something personnel carry directly to the threat.
