Tech Briefs Magazine - May 2022 - 31

(UV) laser is activated to illuminate the
particle and multiband laser-induced fluorescence
is collected.
The detection process continues as an
embedded logic decision, referred to as
the " spectral trigger, " uses scattering from
the NIR light and UV fluorescence data
to predict if the particle's composition appears
to correspond to that of a threat-like
bioagent. If the particle seems threat-like,
then spark-induced breakdown spectroscopy
is enabled to vaporize the particle
and collect atomic emission to characterize
the particle's elemental content.
Spark-induced breakdown spectroscopy
is the last measurement stage. This
spectroscopy system measures the elemental
content of the particle and its measurements
involve creating a high-temperature
plasma, vaporizing the aerosol
particle, and measuring the atomic emission
from the thermally excited states
of the aerosol. The measurement stages
are integrated into a tiered system that
provides seven measurements on each
particle of interest. Of the hundreds of
particles entering the measurement process
each second, a small subset of particles
is down-selected for measurement
in all three stages. The RAAD algorithm
searches the data stream for changes in
the particle set's temporal and spectral
characteristics. If a sufficient number of
threat-like particles are found, the RAAD
issues an alarm that a biological aerosol
threat is present.
To improve detection reliability, the
RAAD team chose to use carbon-filtered,
HEPA-filtered, and dehumidified sheathing
air and purge air (compressed air that
pushes out extraneous gases) around the
optical components. This approach ensures
that contaminants from the outside
air do not deposit onto the optical surfaces
of the RAAD, potentially causing reductions
in sensitivity or false alarms.
For more information, contact Dorothy
Ryan at dryan@ll.mit.edu; 781-981-8616.
The Rapid Agent Aerosol Detector was photographed
with a 12 " ruler to illustrate scale.
(Photo: MIT Lincoln Laboratory)
Electronic Skin Powered by Sweat Serves as HumanMachine
Interface
The e-skin monitors heart rate, body temperature, levels of blood sugar, and metabolic byproducts
that are indicators of health.
California Institute of Technology, Pasadena, CA
R
esearchers have developed electronic
skin (e-skin) that is applied
directly on top of real skin.
Made from soft, flexible rubber, it
can be embedded with sensors that
monitor information like heart rate,
body temperature, levels of blood
sugar,
and metabolic
byproducts
that are indicators of health as well
as nerve signals that control muscles.
It does so without the need for a battery,
as it runs solely on biofuel cells
powered by one of the body's own
waste products.
Human sweat contains very high
levels of the chemical lactate, a compound
generated as a byproduct of
normal metabolic processes, especially
by muscles during exercise. The
fuel cells built into the e-skin absorb
that lactate and combine it with oxygen
from the atmosphere, generating
water and pyruvate, another byproduct
of metabolism. As they operate, the
biofuel cells generate enough electricity
to power sensors and a Bluetooth
device similar to the one that connects
Tech Briefs, May 2022
more attractive approach with extended
connectivity for practical medical
and robotic applications.
Devising a power source that could
Made from soft, flexible rubber, the electronic skin is applied
directly on top of real skin. (Photo: CalTech)
a phone to a car stereo, allowing the
e-skin to transmit readings from its sensors
wirelessly.
While near-field communication is a
common approach for many battery-free
e-skin systems, it could be only used for
power transfer and data readout over a
very short distance. Bluetooth communication
consumes higher power but is a
www.techbriefs.com
run on sweat was not the only challenge
in creating the e-skin. It also needed to
last a long time with high power intensity
with minimal degradation. The biofuel
cells are made from carbon nanotubes
impregnated with a platinum/
cobalt catalyst and composite mesh
holding an enzyme that breaks down
lactate. They can generate continuous,
stable power output (as high as several
milliwatts per square centimeter) over
multiple days in human sweat.
Next steps are to develop a variety
of sensors that can be embedded in
the e-skin so it can be used for multiple
purposes. In addition to being a wearable
biosensor, this can be a human-machine
interface - the vital signs and molecular
information collected using this platform
could be used to design and optimize
next-generation prosthetics.
For more information, contact Emily Velasco
at evelasco@caltech.edu; 626-395-6487.
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Tech Briefs Magazine - May 2022

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