Dartmouth researchers have built a smartphone-based system that measures oxygen inside tissues using a natural cell molecule. The low-cost tool could one day help patients track wounds, infections and limb health from home.
A Dartmouth engineering team has turned an ordinary smartphone into a powerful window into tissue health, using a natural molecule inside our cells to measure how much oxygen they are getting.
The experimental tool, part of a study published in the journal Biosensors and Bioelectronics, could pave the way for simple, low-cost monitoring of conditions such as peripheral vascular disease, chronic wounds and serious infections — potentially from a patient’s own home.
Today, most people are familiar with fingertip pulse oximeters, which measure how much oxygen is carried in the blood. Those devices are crucial in emergency rooms, ambulances and home care, but they only tell part of the story.
“The pulse oximeters used in emergency rooms, ambulances, and home care effectively measure blood oxygen, but that actually doesn’t change much until you’re basically near death,” co-author Brian Pogue, the Robert A. Pritzker Professor of Biomedical Engineering at Dartmouth, said in a news release. “What we really want is not the blood oxygen, but the tissue oxygen. That’s a much more subtle indicator of tissue function and a better dynamic indicator of health.”
Tissue oxygen levels can reveal how well blood is actually reaching organs and limbs, and how those tissues are functioning over time. Doctors use that information to decide when to perform vascular surgery, when a limb is too damaged to save, and how wounds are healing. But current methods to measure tissue oxygen often rely on bulky, expensive camera systems or invasive sensors that are typically used only in hospitals.
The Dartmouth team, based at the Thayer School of Engineering, set out to shrink that capability into something as simple as a phone. Their system combines a regular smartphone camera, a pulsed LED light and, in some cases, a topical cream.
The cream boosts production of a molecule called Protoporphyrin IX, which is naturally present in all living cells and is sensitive to oxygen. When exposed to the right kind of light, this molecule briefly glows — unless oxygen is present to quench that glow.
“It has a useful quirk that when activated, it’s quenched by oxygen,” Pogue added. “When Protoporphyrin IX is not quenched by oxygen, it emits a tiny light signal. That’s what our measurement tool is picking up.”
By flashing the LED and recording the delayed light signal with the phone’s camera over time, the system can infer how much oxygen is in the tissue. The idea of using smartphones as time-sequenced measurement tools has been explored in other areas, but, as Pogue pointed out, “nobody has used them for tissue oxygen before,” so the team had to figure out how to pair the phone with a molecule that already exists in the body as an oxygen reporter.
In their study, the researchers tested the approach on animal tissue samples to show that the smartphone readout could track intracellular oxygen levels in living tissue. While more work is needed before the technology can be used in human patients, the proof-of-concept suggests a path toward far more accessible monitoring.
One major potential use is in peripheral vascular disease, where narrowed or blocked blood vessels reduce blood flow to the limbs. Many patients with severe disease face difficult decisions about surgery or amputation, and clinicians rely heavily on tissue-oxygen measurements to guide those calls.
“So, for somebody who has limb atrophy, the ability to use a cell phone for day-to-day monitoring of tissue oxygen has a lot of value for making major health decisions,” added Pogue.
The system could also help track how wounds and infections are healing. In those cases, Pogue explained, the setup can be even simpler because inflamed tissue naturally produces more Protoporphyrin IX, eliminating the need for the activating cream. Inflamed tissue tends to stay well oxygenated while it repairs itself, then oxygen levels and Protoporphyrin IX production drop as inflammation subsides.
“Any inflammatory response in tissue already increases production of Protoporphyrin IX,” Pogue said. “It’s the trend over time that matters.”
That focus on trends makes the simplicity and low cost of a phone-based tool especially important. Instead of relying on a few snapshots taken with expensive hospital equipment, patients and clinicians could, in principle, collect frequent measurements over days or weeks to see how a condition is evolving.
The team is already expanding testing to explore new applications.
“We started another study with a surgeon in Wisconsin who does burn care,” Pogue added. “She’s monitoring her patients right now to look at Protoporphyrin IX levels and oxygen in burned tissue to see if it’s diagnostic for when to do a skin graft.”
In burn care, deciding when to graft skin can be critical to recovery, and repeated imaging with large camera systems can be impractical and costly. As Pogue put it, “That’s when expensive camera systems don’t make a lot of sense.”
To move the technology closer to real-world use, the researchers are also working on the user experience. They have enlisted undergraduate students through Dartmouth’s First-Year Research in Engineering Experience program to help design a smartphone app that can guide users through measurements and display results in a clear, actionable way.
The goal, Pogue added, is “[s]omething easy and intuitive for daily monitoring that can open up this area of medicine to being cost-effective and doable,” especially for people who live far from major medical centers or who need long-term follow-up.
While the current study focused on animal tissue and technical validation, the broader vision is to democratize access to sophisticated tissue-oxygen monitoring. If future clinical trials in humans are successful and regulators approve the technology, a device most people already carry in their pockets could become a powerful ally in managing chronic disease, guiding treatment and catching problems earlier.
For students and young researchers, the project also highlights how combining basic biology, optics and everyday technology can open new frontiers in health care — and potentially put life-saving information into the hands of patients themselves.
Source: Dartmouth Engineering