A newly-developed diamond magnetometer is small enough for keyhole surgery, and sensitive enough to detect magnetic tracer fluid used by surgeons to locate metastasized cancer cells.
The sensor was originally developed by Alex Newman, PhD student at the University of Warwick, UK, to detect damage in nuclear waste containers. But after speaking with a breast cancer surgeon, Gavin Morley, group leader and professor in the Physics Department at Warwick, decided to change track.
We spoke with Morley to find out more.
What convinced you that diamonds could work as the basis of a tumor-finding probe?
We work on lots of applications for our sensors: besides the medical applications, we’d like to put them into space, use them to help build future fusion power plants, and also to allow people to communicate with their computers just with their thoughts.
For Alex’s project, we were working on detecting damage in steel to help the National Nuclear Lab, which has nuclear waste stored in steel containers. But then I met Stuart Robertson, who is a breast cancer surgeon at the University Hospitals Coventry and Warwickshire: he told me about how useful the Endomag solution (an iron oxide suspension) is for detecting breast cancer metastasis, and I thought we could build a magnetometer that would help.
Can you explain how, in a nutshell, it works?
We’ve been building magnetic field sensors using diamonds and lasers in my research group for ten years. We use diamonds that have been grown specially in a lab to have a lovely pink color because of the quantum defects – called nitrogen vacancy centers – added to them. Our specialty is using optic fibers to send the laser light to the diamond and detect the red light that comes back. Also, when we send microwaves to the diamond, the amount of red light we get back depends on the magnetic field the diamond sees. This is because the nitrogen vacancy centers have quantum properties very similar to atoms.
Alex Newman is a PhD student in my group who built this new laparoscopic sensor. He likes fixing old sports cars and I love how he applied that thinking to this new technology. He gets into the lab and tries things out, which means that twice he’s built cool diamond sensors that no-one has managed to build before. He’ll often use things like BluTack along the way, which is probably surprising to some people.
To build this sensor Alex glued a small diamond – specially grown by a company called Element Six in Oxfordshire – to the end of an optic fiber. Then he put a microwave wire in to send microwaves to the diamond, covered it all with a white paste to keep the light in, before putting a small magnet onto the optical fiber to help the diamond sensor improve sensitivity. Finally, he put a plastic cap on the end.
What was the toughest design compromise you faced when miniaturizing the technology?
Getting the magnet in was tricky – we'd have preferred to use a larger magnet further away to improve the sensitivity of the magnetometer, but we also needed the diamond be close to the magnetic tracer fluid we want to sense. Alex designed it with a small magnet that is close to the magnetic tracer fluid, and he found that the sensitivity was still good enough.
Were there any major surprises or breakthrough moments during the research?
Some experts thought that it would take a lot of development work to be able to detect the magnetic tracer fluid with such a small sensor. Alex made it work much faster than this.
How do you see surgeons actually using the probe in practice? Did you collaborate with clinicians during the study?
During this study we worked with Stuart Robertson (a breast cancer surgeon) and Joseph Hardwicke (a skin cancer surgeon) from the University Hospitals Coventry and Warwickshire.
The exciting thing about our paper is that we’ve built a diamond magnetometer that is small enough for keyhole surgery, while still being sensitive enough to detect the magnetic tracer fluid surgeons use to find where cancer has spread to. It’s really bad news when cancer spreads from its original site, and so it’s crucial to find this as soon as possible. The new cancer is called metastatic cancer, “mets” for short, and it’s often in the lymph nodes. One existing technique to find mets is to use MRI or CT – but a sentinel lymph node biopsy can find mets that are one thousand times smaller. Finding mets when they’re so small hugely improves the chances of surviving cancer. However, sentinel lymph node biopsy is an expensive operation so you don’t want to do it if there are no mets there.
A spin out company called Endomag provided a solution to hospitals which involves the surgeon injecting a magnetic tracer fluid into a breast cancer tumor – because the tracer fluid goes to the lymph nodes that have mets. A magnetometer is then used to find the magnetic tracer fluid and so the surgeon can remove these cancerous lymph nodes. Before the magnetic solution, radioactive tracer fluids were used ,but these require a lot of safety precautions that are too expensive for many hospitals. A cheap solution is to use a blue dye, but one in a hundred people are allergic to it.
This magnetic technique to find mets is great for breast cancer, but the magnetometers used are too large for keyhole surgery or endoscopy. We want to create a magnetometer that can be used to find the mets from other cancers, so we’re building a version that’s smaller than the Endomag probe. The surgeons we talk to say that colorectal cancer could be the best place for us to focus on at first.
Finally, beyond cancer surgery, where do you see the biggest opportunities for diamond magnetometry to make an impact?
We think that magnetoencephalography will be a great application: detecting the magnetic fields that come from our brains when we think.
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