Do sweat it! Wearable microfluidic sensor to measure lactate
concentration in real time
Scientists develop new biosensing device to chemically monitor the state
of muscles during physical exercise

Date:
February 17, 2021
Source:
Tokyo University of Science
Summary:
Lactate, a compound present in sweat, is an important biomarker
to quantify during exercise. However, available wearable sensors
can cause skin irritation, which calls for the use of different
materials. In a recent study, scientists have developed a soft and
nonirritating microfluidic sensor for the real-time measurement
of lactate concentration in sweat. This wearable device will help
monitor the state of the body during intense physical exercise
or work.



FULL STORY ==========================================================================
With the seemingly unstoppable advancement in the fields of
miniaturization and materials science, all sorts of electronic devices
have emerged to help us lead easier and healthier lives. Wearable
sensors fall in this category, and they have received much attention
lately as useful tools to monitor a person's health in real time. Many
such sensors operate by quantifying biomarkers, that is, measurable
indicators that reflect one's health condition. Widely used biomarkers
are heartrate and body temperature, which can be monitored continuously
with relative ease. On the contrary, chemical biomarkers in bodily fluids,
such as blood, saliva, and sweat, are more challenging to quantify with wearable sensors.


==========================================================================
For instance, lactate, which is produced during the breakdown of
glucose in the absence of oxygen in tissues, is an important biomarker
present in both blood and sweat that reflects the intensity of physical exercise done as well as the oxygenation of muscles. During exercise,
muscles requiring energy can rapidly run out of oxygen and fall back
to a different metabolic pathway that provides energy at the 'cost'
of accumulating lactate, which causes pain and fatigue.

Lactate is then released into the bloodstream and part of it is eliminated through sweat. This means that a wearable chemical sensor could measure
the concentration of lactate in sweat to give a real-time picture of
the intensity of exercise or the condition of muscles.

Although lactate-measuring wearable sensors have already been proposed,
most of them are composed of materials that can cause irritation of the
skin. To address this problem, a team of scientists in Japan recently
carried out a study to bring us a more comfortable and practical
sensor. Their work, which was published in Electrochimica Acta, was
led by Associate Professor Isao Shitanda, Mr. Masaya Mitsumoto, and
Dr. Noya Loew from the Department of Pure and Applied Chemistry at the
Tokyo University of Science, Japan.

The team first focused on the sensing mechanism that they would employ
in the sensor. Most lactate biosensors are made by immobilizing lactate
oxidase (an enzyme) and an appropriate mediator on an electrode. A
chemical reaction involving lactate oxidase, the mediator, and free
lactate results in the generation of a measurable current between
electrodes -- a current that is roughly proportional to the concentration
of lactate.

A tricky aspect here is how to immobilize the enzyme and mediator on an electrode. To do this, the scientists employed a method called "electron
beam- induced graft polymerization," by which functional molecules
were bonded to a carbon-based material that can spontaneously bind to
the enzyme. The researchers then turned the material into a liquid ink
that can be used to print electrodes. This last part turns out to be
an important aspect for the future commercialization of the sensor, as
Dr. Shitanda explains, "The fabrication of our sensor is compatible with
screen printing, an excellent method for fabricating lightweight, flexible electrodes that can be scaled up for mass production." With the sensing mechanism complete, the team then designed an appropriate system for
collecting sweat and delivering it to the sensor. They achieved this with
a microfluidic sweat collection system made out of polydimethylsiloxane
(PDMS); it comprised multiple small inlets, an outlet, and a chamber for
the sensor in between. "We decided to use PDMS because it is a soft, nonirritating material suitable for our microfluidic sweat collection
system, which is to be in direct contact with the skin," comments
Mr. Mitsumoto.

The detection limits of the sensor and its operating range for lactate concentrations was confirmed to be suitable for investigating the "lactate threshold" -- the point at which aerobic (with oxygen) metabolism turns
into anaerobic (without oxygen) metabolism during exercise. Real-time monitoring of this bodily phenomenon is important for several
applications, as Dr. Loew remarks, "Monitoring the lactate threshold
will help optimize the training of athletes and the exercise routines of rehabilitation patients and the elderly, as well as control the exertion
of high-performance workers such as firefighters." The team is already
testing the implementation of this sensor in practical scenarios. With
any luck, the progress made in this study will help develop the field
of wearable chemical sensors, helping us to keep better track of our
bodily processes and maintain better health.

========================================================================== Story Source: Materials provided by Tokyo_University_of_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Isao Shitanda, Masaya Mitsumoto, Noya Loew, Yuko Yoshihara, Hikari
Watanabe, Tsutomu Mikawa, Seiya Tsujimura, Masayuki Itagaki,
Masahiro Motosuke. Continuous sweat lactate monitoring system with
integrated screen-printed MgO-templated carbon-lactate oxidase
biosensor and microfluidic sweat collector. Electrochimica Acta,
2021; 368: 137620 DOI: 10.1016/j.electacta.2020.137620 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/02/210217151031.htm

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