Over the past few years, Profusa Inc has been developing tiny biosensors that get injected under the skin, and then provide the user with health information via their smartphone. The technology was recently approved for marketing in Europe, with US approval possibly following soon.

Each sensor is smaller than a grain of rice, has a scaffold-like structure, and is made of a hydrogel based on a polymer commonly used for soft contact lenses. That polymer is festooned with dye molecules.

Due their small size, high flexibility, and the fact that they lack any unnatural flat surfaces, the sensors aren't recognized by the immune system as foreign objects. As a result, they don't get covered in inflammatory cells or scar tissue, which would isolate them and keep them from detecting chemical changes in the body. Instead, cells and capillaries actually grow into the sensors' scaffolding, incorporating them into the surrounding tissue.

The sensors subsequently remain active for a period of months to years – in fact, the first sensors implanted in human test subjects are still functioning after over four years.

To "read" them, users utilize a handheld detector or an adhesive electronic patch, which shines near-infrared light through the skin. This causes the dye molecules to fluoresce. The degree to which they fluoresce is determined by relative concentrations of certain biochemicals within the body – different types of dye molecules react to different chemicals, such as oxygen, carbon dioxide, glucose or lactate.

The detector/patch measures the amount of fluorescence emitted by the sensor, and wirelessly transmits the data to an app on the user's smartphone. That app analyzes the data, compares the present chemical concentrations to a baseline for that person, then lets them know if there are any health issues that they need to be aware of.

In Europe, the sensors are already being used to monitor tissue oxygen levels in patients being treated for peripheral artery disease, which can lead to amputations if left unchecked. The technology is also being tested in a clinical trial at the University of California, San Francisco, tracking oxygen levels in patients with chronic foot wounds.

The sensors could additionally be used to monitor oxygen levels around muscles to assess peoples' fitness levels, and to help athletes train more effectively. They may also find use with US Army, which has expressed an interest in using the technology to remotely monitor the well-being of soldiers, and to help in the triage process on battlefields.

The latest research on the Profusa sensors was presented this Monday, at the 255th National Meeting & Exposition of the American Chemical Society.