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Engineers at the University of California San Diego have
developed a miniature, ultra-low power injectable biosensor that could be used
for continuous, long-term alcohol monitoring. The chip is small enough to be
implanted in the body just beneath the surface of the skin and is powered
wirelessly by a wearable device, such as a smartwatch or patch.
The ultimate goal of this work is to develop a routine,
unobtrusive alcohol and drug monitoring device for patients in substance abuse
One of the challenges for patients in treatment programs is the
lack of convenient tools for routine monitoring. Breathalyzers, currently the
most common way to estimate blood alcohol levels, are clunky devices that
require patient initiation and are not that accurate. A blood test is the
most accurate method, but it needs to be performed by a trained technician.
Tattoo-based alcohol sensors that can be worn on the skin are a promising new
alternative, but they can be easily removed and are only single-use.
A tiny injectable sensor - that can be administered in a clinic
without surgery - could make it easier for patients to follow a prescribed
course of monitoring for extended periods of time.
The biosensor chip measures roughly one cubic millimeter in size
and can be injected under the skin in interstitial fluid - the fluid that
surrounds the body's cells. It contains a sensor that is coated with alcohol
oxidase, an enzyme that selectively interacts with alcohol to generate a
byproduct that can be electro-chemically detected. The electrical signals are
transmitted wirelessly to a nearby wearable device such as a smartwatch, which
also wirelessly powers the chip. Two additional sensors on the chip measure
background signals and pH levels. These get canceled out to make the alcohol
reading more accurate.
The researchers designed the chip to consume as little power as
possible; the number is 970 nanowatts total, which is roughly one million times
less power than a smartphone consumes when making a phone call. They wanted to
make sure the chip was not a significant drain on the battery life of the
wearable device. And since it's implanted, they don't want a lot of heat being
locally generated inside the body.
One of the ways the chip operates on such ultra-low power is by
transmitting data via a technique called backscattering. This occurs when a
nearby device like a smartwatch sends radio frequency signals to the chip, and
the chip sends data by modifying and reflecting those signals back to the
smartwatch. The researchers also designed ultra-low power sensor readout
circuits for the chip and minimized its measurement time to just three seconds,
resulting in less power consumption.
The researchers tested the chip in vitro with a setup that
mimicked an implanted environment. This involved mixtures of ethanol in diluted
human serum underneath layers of pig skin.
For future studies, the researchers are planning to test the
chip in live animals and to optimize the chip for next-generation rehab
monitoring. They are alos developing versions of this chip that can monitor
other molecules and drugs in the body.
As the researchers put it, "This is a proof-of-concept platform
technology. We've shown that this chip can work for alcohol, but we envision
creating others that can detect different substances of abuse and injecting a
customized cocktail of them into a patient to provide long-term, personalized