The new device, developed by Dae-Hyeong Kim and colleagues at Seoul National University and the Institute of Basic Science, can be worn very close to the skin, just like a temporary tattoo, thanks to it being ultrathin. What's more, it is not only flexible but can mechanically deform and stretch as the patient moves. And since it is made from closely-packed gold nanoparticles (which form a flash memory module floating gate) on a stretchable silicon membrane, it can also store more memory from recorded data than previous such monitors. The gold nanoparticle floating gates also show much more stable data storage performance than previous memory devices made from conducting films containing metals or carbon nanotubes.

The monitor itself also contains electrocardiogram (ECG) sensors and amplifiers that continually and accurately measure heart rate. Indeed, the device encodes heart rate data as binary code that is then converted into decimal numbers for easy readability. Kim's team has already tested out its device on patients and confirms that it can reliably store heart rate data, as extracted from sample ECG signals.

Portable devices that can be worn by patients have come a long way in the last few years thanks, in part, to important advances in flexible electronics and devices that can mould themselves to the soft structure of skin and tissue. Indeed, a host of novel biocompatible applications, such as patch-like thermometers that stick to the skin and electronic circuits that interface with internal organs such as the heart and brain, have already been developed. Sophisticated though such structures are, most of them are unable to independently store recorded data in memory modules during long-term patient monitoring. Also missing is their ability to stretch and deform as a patient moves.

The new device overcomes all these problems and more. "The advances in characterization and fabrication technologies reported in this work will be an important stepping stone that will pave the way to fully integrated wearable systems composed of stretchable nanocrystal floating-gate memory devices and other stretchable silicon electronics toward mobile and personalized health monitoring," the researchers write.

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