Wearable Device Tracks Individual Cells in Bloodstream in Real Time

One key feature of this wearable device is its ability to continuously monitor circulating cells in the human body. This technology, presented in npj Biosensing, has the potential to significantly enhance early disease diagnosis, monitor disease relapse, assess infection risk, and determine the effectiveness of treatments, among other medical applications.

The device, named CircTrek, was developed by researchers at the Massachusetts Institute of Technology (MIT, Cambridge, MA, USA) to provide real-time assessments, unlike traditional blood tests that offer only a snapshot of a patient's condition. Existing technologies like in vivo flow cytometry, which also monitor cells in the bloodstream continuously, require large, room-sized microscopes, and patients must remain in the facility for extended periods. In contrast, CircTrek, equipped with an onboard Wi-Fi module, can monitor circulating cells at home and transmit the data to the patient’s healthcare provider. The device works by directing a focused laser beam to stimulate fluorescently labeled cells beneath the skin. This labeling can be achieved using various methods, such as applying antibody-based fluorescent dyes or genetically modifying cells to express fluorescent proteins.

For instance, a patient undergoing CAR T cell therapy—where immune cells are collected, modified in a lab to fight cancer, and reintroduced into the body—could have the modified cells labeled with fluorescent dyes or genetic modifications. These labeled cells, once circulating in the bloodstream, can then be detected by CircTrek. This capability is especially valuable in tracking whether a treatment, like CAR T cell therapy, is effective. The persistence of CAR T cells in the blood after treatment is associated with better outcomes in patients with B-cell lymphoma. To keep CircTrek small and wearable, the researchers miniaturized the device components, including the circuit that powers the high-intensity laser and maintains stable laser output to avoid false readings. The sensor that detects the fluorescent signals from the labeled cells is also compact, yet sensitive enough to detect light corresponding to a single photon. The subcircuits, such as the laser driver and noise filters, were custom-designed to fit on a circuit board measuring just 42 mm by 35 mm, making CircTrek roughly the size of a smartwatch.

CircTrek underwent testing in an in vitro configuration that simulated blood flow beneath human skin, and its single-cell detection ability was validated through manual counting with a high-resolution confocal microscope. For the in vitro tests, a fluorescent dye called Cyanine5.5 was used, selected for its peak activation at wavelengths within the optical window of skin tissue—the range of light that can penetrate the skin with minimal scattering. The safety of the device, particularly the temperature increase in experimental skin tissue due to the laser, was also assessed. A surface temperature increase of 1.51 degrees Celsius was found to be well below the threshold that would cause tissue damage, leaving enough of a margin to allow for safe expansion of the device’s detection area and power. Although further steps are required for clinical application, researchers believe that CircTrek’s parameters can be adjusted to extend its capabilities, potentially providing critical data for doctors on a wide range of patients.

“CircTrek offers a path to harnessing previously inaccessible information, enabling timely treatments, and supporting accurate clinical decisions with real-time data,” said Deblina Sarkar, assistant professor at MIT, who led the research team. “Existing technologies provide monitoring that is not continuous, which can lead to missing critical treatment windows. We overcome this challenge with CircTrek.”