Diamond Trace Detector: Endoscopic Quantum Magnetometer Will Tell Surgeon Where to Look for Sentinel Lymph Nodes

Physicists from the University of Warwick have demonstrated a prototype of an endoscopic diamond magnetometer for oncosurgery. The sensor uses nitrogen-vacancy (NV) centers in diamond and reads magnetic fields from the iron oxide tracer MagTrace™ - the same one used in sentinel lymph node biopsy in breast surgery. The device records an iron mass of only 0.56 mg at a distance of up to 5.8 mm - this is approximately 100 times less than the recommended dose of the tracer; at higher concentrations, the working distance increases to 14.6 mm. The diameter of the sensor "head" is no more than 10 mm, so it can be installed on endoscopes and laparoscopes.

Background of the study

Sentinel lymph node biopsy (SLNB) is the standard for staging early breast cancer and a number of other tumors: the "first" nodes along the lymphatic drainage are removed to understand whether the tumor has gone into the lymphatic system, avoiding more traumatic dissection. Classic navigation is a radioisotope + blue dye, but the method has its drawbacks: radiological logistics, limited time windows, rare allergic reactions and limitations for minimally invasive procedures. Therefore, alternatives are actively developing - superparamagnetic iron oxides (SPIO), for example, the clinical tracer MagTrace®, approved by NICE and FDA in combination with the Sentimag probe. Such markers can be introduced minutes or weeks before surgery, they remain in the nodes and are visible with magnetic sensors in the operating room.

However, existing magnetic probes are typically hand-held devices with a permanent magnet and a Hall sensor: they work, but the sensitivity and form factor limit their use in endoscopy and laparoscopy, and the detection threshold encourages the use of full-dose tracer injections. The ideal tool for the surgeon is a miniature, sterile-compatible probe that can “see” very small amounts of SPIO at centimeter distances and operate without massive magnetizing magnets.

Against this background, quantum sensors on diamond appear to be a promising platform: nitrogen-vacancy (NV) centers in diamond make it possible to optically read the magnetic field (ODMR) at room temperature, without cryogens; devices can be made fiber-optic, taking lasers and detectors out of the sterile zone. In recent years, compact NV magnetometers have been demonstrated for biomedical applications, including for recording signals from magnetic nanoparticles. Review papers systematize ways to increase sensitivity and confirm the potential of NV diamond as a platform for applied magnetometers.

A new development from the University of Warwick closes this gap: an endoscopic NV diamond magnetometer has been presented that detects the clinical tracer MagTrace®. The prototype detects iron mass up to 0.56 mg at a distance of up to 5.8 mm (≈100 times less than the recommended dose) and works with concentrations up to 2.8 mg/ml at a distance of up to 14.6 mm; the diameter of the sensor “head” ≤10 mm is compatible with endoscopes and laparoscopes. If these parameters are confirmed in vivo, the technology can reduce the required tracer doses, simplify navigation in minimally invasive surgery and reduce dependence on radioisotopes. For now, this is a laboratory prototype that awaits calibration in living tissue and head-to-head comparison with existing systems, but the “quantum” path to the clinic is already visible.

How does this work

Inside the sensor is a microcrystal of diamond with NV impurities. A green laser and a microwave signal tune the NV centers, and their luminescence changes when they enter a magnetic field. This optical resonance reading (ODMR) provides high sensitivity at room temperature, without cryogens and superconductors. In the new device, the diamond "head" is connected by optical fiber to the rest of the optics: all the heavy electronics remain outside the sterile field, and only a miniature sensor is brought to the patient - convenient for the operating room.

Why do oncology surgeons need this?

In breast cancer (and a number of other tumors), it is important for the surgeon to accurately find and remove sentinel lymph nodes - those where tumor cells go first. Magnetic tracers based on superparamagnetic iron oxide are a safe alternative to radioisotopes and dyes (with anesthetic and allergic risks). A quantum diamond sensor adds delicacy and compactness to this technique: the lower the detection threshold and the smaller the sensor, the earlier and more conveniently you can see the "magnetic trace" of the node - up to endoscopic procedures.

Key facts and figures

• Iron mass threshold: 0.56 mg detected at a distance of up to 5.8 mm (≈100× less than the recommended dose).
• Concentration threshold: 2.8 mg/ml (≈20× less than recommended) - with a working distance of up to 14.6 mm.
• Sensor dimensions: “head” ≤10 mm in diameter - compatible with endoscopy/laparoscopy.
• Application: detection of the iron oxide tracer MagTrace™ (Endomag/Endomagnetics) in breast surgery.

How is this different from existing probes?

Currently, operating rooms use manual magnetic sensors with a permanent magnet and a Hall sensor - they have proven their functionality, but their sensitivity and format are limited. Diamond NV magnetometer:

• works without magnetization by massive magnets,
• reads weak fields from small amounts of tracer,
• fits into an endoscopic form factor,
• allows fiber optics to be removed outside the sterile zone.

What does this mean for the patient (and the operating room)

In an ideal scenario, the surgeon gets a "quantum pointer": holding a thin probe to the tissue, he sees where the magnetic trace of the tracer is stronger - and looks for the sentinel node there. This can:

• reduce search time and volume of cuts;
• reduce the dose of the administered tracer (while maintaining reliability);
• assist in minimally invasive interventions - in the chest, abdomen, pelvis;
• reduce dependence on radioisotopes and nuclear marking logistics.

Context and independent assessments

The publication in Physical Review Applied is open access and licensed under CC BY 4.0; the University of Warwick issued a press release, “Diamonds that help find cancer,” highlighting the portability and endoscopic diameter of the probe. Specialized publications for doctors and engineers note that sensitivity below clinical doses is an important step towards a real operating room.

What else needs to be checked (an honest to-do list)

• Sterility and ergonomics: disposable “covers”, attachment to endoscopes, convenience for assistants.
• Calibrations in living tissue: the influence of blood, fat, node depth and metal instruments on the signal.
• Head-to-head comparisons: versus current magnetic probes and radionuclide navigation - in terms of accuracy, time and "false targets".
• Regulatory path: EMC standards and evidence base for approval in different countries.

Why diamond and NV centers

NV centers have quantum sensitivity to magnetic fields and optical signal reading: this combination allows building compact, stable sensors that operate at room temperature. This is critical for medicine: no cryogens, quick start-up, modularity (laser and photodetector are removed from the patient via optical fiber), potential for scaling into clinical batches.

Conclusion

The new endoscopic diamond magnetometer confidently “sees” the magnetic trace of a clinical tracer at doses lower than usual and fits into a 10-mm form factor. If upcoming tests confirm stability in the operating environment, surgeons will have a quantum, compact and gentle assistant for finding sentinel lymph nodes - from open surgeries to laparoscopy and endoscopy. This is a rare case when quantum sensorics is almost ready to cross the threshold into a real clinic.

Source: AJ Newman et al. Endoscopic diamond magnetometer for cancer surgery. Physical Review Applied 24, 024029 (12 August 2025). DOI: https://doi.org/10.1103/znt3-988w