This wearable device can track individual cells in the bloodstream in real time

Imagine a smartwatch that doesn't just track your steps or heart rate — but watches your blood, cell by cell, in real time. That's no longer science fiction. A team at MIT has built CircTrek, a sleek wearable so sensitive it can detect individual cells cruising through your bloodstream, all while strapped to your wrist.

"CircTrek offers a path to harnessing previously inaccessible information, enabling timely treatments, and supporting accurate clinical decisions with real-time data," says Deblina Sarkar, the project's lead and assistant professor at MIT. This tiny gadget might just turn how we detect and treat diseases on its head.

How does it work?

• CircTrek shoots a finely focused laser beam under your skin to spot fluorescently labeled cells floating by in your blood.
• Those labels? They can come from dyes or genetic tweaks — either done in the lab or via approved in vivo methods in patients.
• Once the laser lights up those cells, a mini sensor catches the glow, while smart filters block out noise from things like your heartbeat.

As Ph.D. student Kyuho Jang puts it, "We optimized the optomechanical parts to reduce noise significantly and only capture the signal from the fluorescent cells."

All that high-tech wizardry fits onto a circuit board smaller than a Post-it note — just 42 by 35 millimeters — making CircTrek no bulkier than your average smartwatch.

Why does it matter?

Right now, blood tests are like still photos — you get a quick peek into what's going on in the body, then it's over. But disease doesn't wait for your next lab appointment.

• Real-time cell tracking could reveal whether a cancer treatment is working as it happens.
• Patients on therapies like CAR T cell treatment could know if the modified cells are still active, which can make or break an outcome.
• Doctors could catch signs of infection or relapse days — if not weeks — earlier than with traditional tests.

And unlike clunky in-clinic gear, which "requires a room-sized microscope, and patients need to be there for a long time," says Jang, CircTrek brings the lab to the living room. It's got Wi-Fi, meaning data can beam straight to your doctor, even while you're lounging on the couch.

The context

This kind of minute-by-minute insight has been called an "unmet goal to date" in the field of biosensing. Until now, in vivo flow cytometry — the gold standard — has required specialized facilities and hours of patient time.

But CircTrek is different. It's lightweight. It's wearable. And it works.

• In tests, it spotted fluorescent signals as faint as a single photon.
• The team used a dye called Cyanine5.5, specially chosen because it works within the skin's optical window.
• Safety? Covered. At its peak, the device warmed skin by just 1.51°C — far below any harmful threshold.

Sure, it's still early days. Clinical trials lie ahead, and plenty of tweaks will be needed before CircTrek lands in your medicine cabinet. But the potential? Massive.

As Sarkar puts it: "Existing technologies provide monitoring that is not continuous, which can lead to missing critical treatment windows. We overcome this challenge with CircTrek."

Would you wear a device that watches your blood like a hawk?