Reviewed by Lexie CornerApr 29 2025
Researchers at the Massachusetts Institute of Technology have developed a non-invasive medical monitoring tool that is small enough to be worn like a wristwatch and capable of identifying individual blood vessel cells. One of its key features is its ability to continuously monitor circulating cells in the body.
The device, called CircTrek, was created by researchers from the Nano-Cybernetic Biotrek research group, led by Deblina Sarkar, an Assistant Professor at MIT and the AT&T Career Development Chair at the MIT Media Lab.
This technology could significantly improve the speed of early disease diagnosis, relapse detection, infection risk assessment, and treatment effectiveness evaluation.
Whereas traditional blood tests offer a snapshot of a patient's condition, CircTrek was designed to provide real-time assessment.
In vivo flow cytometry, a different technology that provides somewhat continuous bloodstream cell monitoring, “requires a room-sized microscope, and patients need to be there for a long time,” said Kyuho Jang, a Ph.D. Student in Sarkar’s lab.
With its built-in Wi-Fi module, CircTrek can track a patient's circulating cells at home and transmit the data to the patient's physician or care team.
CircTrek offers a path to harnessing previously inaccessible information, enabling timely treatments, and supporting accurate clinical decisions with real-time data. Existing technologies provide monitoring that is not continuous, which can lead to missing critical treatment windows. We overcome this challenge with CircTrek.
Deblina Sarkar, Assistant Professor, Massachusetts Institute of Technology
CircTrek works by stimulating fluorescently labeled cells under the skin using a concentrated laser beam. The labeling can be achieved in several ways, such as introducing antibody-based fluorescent dyes into the target cells or genetically modifying them to express fluorescent proteins.
For example, a patient undergoing CAR T cell therapy may have their immune cells labeled with fluorescent dyes or genetically modified to express fluorescent proteins. CAR T cell therapy involves collecting and modifying immune cells in a lab to fight cancer or, experimentally, to combat diseases like HIV or COVID-19.
Human-approved in vivo labeling techniques can also be used to identify cells of interest. CircTrek uses laser pulses to enhance and detect the fluorescent signal of these labeled cells in circulation, while a series of filters minimizes low-frequency noise, like heartbeats.
We optimized the optomechanical parts to reduce noise significantly and only capture the signal from the fluorescent cells.
Kyuho Jang, PhD Student, Massachusetts Institute of Technology
CircTrek could assess the effectiveness of cell therapy treatments by identifying labeled CAR T cells. For example, patients with B-cell lymphoma who have CAR T cells in their blood after treatment tend to show better outcomes.
One key component of CircTrek is the circuit that powers the high-intensity laser source and maintains its power level to avoid false readings. The researchers managed to reduce the size of this component, making it wearable.
According to Jang, despite its small size, the sensor that detects fluorescent signals from the labeled cells can identify light with an intensity as low as one photon.
The CircTrek is roughly the size of a smartwatch because its subcircuits, including the laser driver and noise filters, were specifically designed to fit on a compact circuit board measuring 42 mm by 35 mm.
The single-cell detection capabilities of CircTrek were confirmed through manual counting using a high-resolution confocal microscope after testing on an in vitro setup that simulated blood flow beneath human skin. Cyanine5.5, a fluorescent dye, was used for the in vitro tests because it activates at wavelengths within the optical window of skin tissue, a range that can pass through the skin with minimal scattering.
The device’s safety was also tested, particularly the effect of the laser's increased temperature on experimental skin tissue. It was found that the temperature increase at the skin's surface was 1.51 °C, which is well below the threshold that would harm tissue. This provides enough of a margin to safely increase the device's detection area and power to observe at least one blood vessel.
According to Jang, while clinical translation will require further work, CircTrek’s parameters can be adjusted to enhance its potential and provide doctors with critical information about a wide range of patients.
Journal Reference:
Jang, K., et al. (2025) A wearable device for continuous monitoring of circulating cells at single-cell resolution. Npj Biosensing. doi.org/10.1038/s44328-025-00032-3.