Tumor growth can be tracked by a tiny white breath mint like capsule. This mechanism avoids invasive procedures.
"With this, we are going to bring the laboratory into the patient," said Michael Cima at the Massachusetts Institute of Technology.
The device is small enough to fit inside a needle and implant in the body during a biopsy, reports New Scientist.
A semi-permeable membrane allows molecules to flow into the capsule, but prevents the nanoparticles from drifting out.
To read the device and evaluate whether a nearby tumour is receding or growing, doctors need only use an MRI scan to detect clusters of cancer-related molecules within the device.
Cima's team tested the device in mice injected with human cancer cells. An MRI showed that the resulting tumours were increasing in size.
In another study with mice, Cima transformed the tumour-monitoring device into a heart-attack detector by lining the inside of the capsule with antibodies that bind to three different proteins released by heart muscle cells when they burst open.
After embedding the devices in the rodents' skin and inducing heart attacks, Cima was able to precisely measure the severity of damage: the more protein accumulated in the monitor, the worse the heart attack and the stronger the MRI signal.
Such a device would be especially useful for people who experience silent heart attacks - which usually present little pain or obvious symptoms - as well as those at risk of a second heart attack.