Tag Archives: sweat

Wearable technology: two types of sensors one from the University of Glasgow (Scotland) and the other from the University of British Columbia (Canada)

Sometimes it’s good to try and pull things together.

University of Glasgow and monitoring chronic conditions

A February 23, 2018 news item on phys.org describes the latest wearable tech from the University of Glasgow,

A new type of flexible, wearable sensor could help people with chronic conditions like diabetes avoid the discomfort of regular pin-prick blood tests by monitoring the chemical composition of their sweat instead.

In a new paper published in the journal Biosensors and Bioelectronics, a team of scientists from the University of Glasgow’s School of Engineering outline how they have built a stretchable, wireless system which is capable of measuring the pH level of users’ sweat.

A February 22, 2018 University of Glasgow press release, which originated the news item, expands on the theme,

Ravinder Dahiya

 Courtesy: University of Glasgow

 

Sweat, like blood, contains chemicals generated in the human body, including glucose and urea. Monitoring the levels of those chemicals in sweat could help clinicians diagnose and monitor chronic conditions such as diabetes, kidney disease and some types of cancers without invasive tests which require blood to be drawn from patients.

However, non-invasive, wearable systems require consistent contact with skin to offer the highest-quality monitoring. Current systems are made from rigid materials, making it more difficult to ensure consistent contact, and other potential solutions such as adhesives can irritate skin. Wireless systems which use Bluetooth to transmit their information are also often bulky and power-hungry, requiring frequent recharging.

The University of Glasgow team’s new system is built around an inexpensively-produced sensor capable of measuring pH levels which can stretch and flex to better fit the contours of users’ bodies. Made from a graphite-polyurethane composite and measuring around a single square centimetre, it can stretch up to 53% in length without compromising performance. It will also continue to work after being subjected to flexes of 30% up to 500 times, which the researchers say will allow it to be used comfortably on human skin with minimal impact on the performance of the sensor.

The sensor can transmit its data wirelessly, and without external power, to an accompanying smartphone app called ‘SenseAble’, also developed by the team. The transmissions use near-field communication, a data transmission system found in many current smartphones which is used most often for smartphone payments like ApplePay, via a stretchable RFID antenna integrated into the system – another breakthrough innovation from the research team.

The smartphone app allows users to track pH levels in real time and was demonstrated in the lab using a chemical solution created by the researchers which mimics the composition of human sweat.

The research was led by Professor Ravinder Dahiya, head of the University of Glasgow’s School of Engineering’s Bendable Electronics and Sensing Technologies (BEST) group.

Professor Dahiya said: “Human sweat contains much of the same physiological information that blood does, and its use in diagnostic systems has the significant advantage of not needing to break the skin in order to administer tests.

“Now that we’ve demonstrated that our stretchable system can be used to monitor pH levels, we’ve already begun additional research to expand the capabilities of the sensor and make it a more complete diagnostic system. We’re planning to add sensors capable of measuring glucose, ammonia and urea, for example, and ultimately we’d like to see a system ready for market in the next few years.”

The team’s paper, titled ‘Stretchable Wireless System for Sweat pH Monitoring’, is published in Biosensors and Bioelectronics. The research was supported by funding from the European Commission and the Engineering and Physical Sciences Research Council (EPSRC).

Here’s a link to and a citation for the paper,

Stretchable wireless system for sweat pH monitoring by Wenting Dang, Libu Manjakkal, William Taube Navaraj, Leandro Lorenzelli, Vincenzo Vinciguerra. Biosensors and Bioelectronics Volume 107, 1 June 2018, Pages 192–202 [Available online February 2018] https://doi.org/10.1016/j.bios.2018.02.025

This paper is behind a paywall.

University of British Columbia (UBC; Okanagan) and monitor bio-signals

This is a completely other type of wearable tech monitor, from a February 22, 2018 UBC news release (also on EurekAlert) by Patty Wellborn (A link has been removed),

Creating the perfect wearable device to monitor muscle movement, heart rate and other tiny bio-signals without breaking the bank has inspired scientists to look for a simpler and more affordable tool.

Now, a team of researchers at UBC’s Okanagan campus have developed a practical way to monitor and interpret human motion, in what may be the missing piece of the puzzle when it comes to wearable technology.

What started as research to create an ultra-stretchable sensor transformed into a sophisticated inter-disciplinary project resulting in a smart wearable device that is capable of sensing and understanding complex human motion, explains School of Engineering Professor Homayoun Najjaran.

The sensor is made by infusing graphene nano-flakes (GNF) into a rubber-like adhesive pad. Najjaran says they then tested the durability of the tiny sensor by stretching it to see if it can maintain accuracy under strains of up to 350 per cent of its original state. The device went through more than 10,000 cycles of stretching and relaxing while maintaining its electrical stability.

“We tested this sensor vigorously,” says Najjaran. “Not only did it maintain its form but more importantly it retained its sensory functionality. We have further demonstrated the efficacy of GNF-Pad as a haptic technology in real-time applications by precisely replicating the human finger gestures using a three-joint robotic finger.”

The goal was to make something that could stretch, be flexible and a reasonable size, and have the required sensitivity, performance, production cost, and robustness. Unlike an inertial measurement unit—an electronic unit that measures force and movement and is used in most step-based wearable technologies—Najjaran says the sensors need to be sensitive enough to respond to different and complex body motions. That includes infinitesimal movements like a heartbeat or a twitch of a finger, to large muscle movements from walking and running.

School of Engineering Professor and study co-author Mina Hoorfar says their results may help manufacturers create the next level of health monitoring and biomedical devices.

“We have introduced an easy and highly repeatable fabrication method to create a highly sensitive sensor with outstanding mechanical and electrical properties at a very low cost,” says Hoorfar.

To demonstrate its practicality, researchers built three wearable devices including a knee band, a wristband and a glove. The wristband monitored heartbeats by sensing the pulse of the artery. In an entirely different range of motion, the finger and knee bands monitored finger gestures and larger scale muscle movements during walking, running, sitting down and standing up. The results, says Hoorfar, indicate an inexpensive device that has a high-level of sensitivity, selectivity and durability.

Hoorfar and Najjaran are both members of the Okanagan node of UBC’s STITCH (SmarT Innovations for Technology Connected Health) Institute that creates and investigates advanced wearable devices.

The research, partially funded by the Natural Sciences and Engineering Research Council, was recently published in the Journal of Sensors and Actuators A: Physical.

Here’s a link to and a citation for the paper,

Low-cost ultra-stretchable strain sensors for monitoring human motion and bio-signals by Seyed Reza Larimi, Hojatollah Rezaei Nejad, Michael Oyatsi, Allen O’Brien, Mina Hoorfar, Homayoun Najjaran. Sensors and Actuators A: Physical Volume 271, 1 March 2018, Pages 182-191 [Published online February 2018] https://doi.org/10.1016/j.sna.2018.01.028

This paper is behind a paywall.

Final comments

The term ‘wearable tech’ covers a lot of ground. In addition to sensors, there are materials that harvest energy, detect poisons, etc.  making for a diverse field.

Enzyme-based sustainable sensing devices

This story about a sustainable sensing device involves sweat. A July 28, 2016 news item on ScienceDaily describes the sweaty situation,

It may be clammy and inconvenient, but human sweat has at least one positive characteristic — it can give insight to what’s happening inside your body. A new study published in the ECS [Electrochemical Society] Journal of Solid State Science and Technology aims to take advantage of sweat’s trove of medical information through the development of a sustainable, wearable sensor to detect lactate levels in your perspiration.

Caption: Depiction of patch sensor via CFDRC. Credit: Sergio Omar Garcia/CFDRC

Caption: Depiction of patch sensor via CFDRC. Credit: Sergio Omar Garcia/CFDRC

The patch in that image doesn’t seem all that wearable but presumably there will be some changes made. A July 28, 2016 Electrochemical Society news release on EurekAlert, which originated the news item, provides more detail about the technology,

“When the human body undergoes strenuous exercise, there’s a point at which aerobic muscle function becomes anaerobic muscle function,” says Jenny Ulyanova, CFD Research Corporation (CFDRC) researcher and co-author of the paper. “At that point, lactate is produce at a faster rate than it is being consumed. When that happens, knowing what those levels are can be an indicator of potentially problematic conditions like muscle fatigue, stress, and dehydration.”

Utilizing green technology

Using sweat to track changes in the body is not a new concept. While there have been many developments in recent years to sense changes in the concentrations of the components of sweat, no purely biological green technology has been used for these devices. The team of CFDRC researchers, in collaboration with the University of New Mexico, developed an enzyme-based sensor powered by a biofuel cell – providing a safe, renewable power source.

Biofuel cells have become a promising technology in the field of energy storage, but still face many issues related to short active lifetimes, low power densities, and low efficiency levels. However, they have several attractive points, including their ability to use renewable fuels like glucose and implement affordable, renewable catalysts.

“The biofuel cell works in this particular case because the sensor is a low-power device,” Ulyanova says. “They’re very good at having high energy densities, but power densities are still a work in progress. But for low-power applications like this particular sensor, it works very well.”

In their research, entitled “Wearable Sensor System Powered by a Biofuel Cell for Detection of Lactate Levels in Sweat,” the team powered the biofuel cells with a fuel based on glucose. This same enzymatic technology, where the enzymes oxidize the fuel and generate energy, is used at the working electrode of the sensor which allows for the detection of lactate in your sweat.

Targeting lactate

While the use of the biofuel cell is a novel aspect of this work, what sets it apart from similar developments in the field is the use of electrochemical processes to very accurately detect a specific compound in a very complex medium like sweat.

“We’re doing it electrochemically, so we’re looking at applying a constant load to the sensor and generating a current response,” Ulyanova says, “which is directly proportional to the concentration of our target analyte.”

Practical applications

Originally, the sensor was developed to help detect and predict conditions related to lactate levels (i.e. fatigue and dehydration) for military personnel.

“The sensor was designed for a soldier in training at boot camp,” says Sergio Omar Garcia, CFDRC researcher and co-author of the paper, “but it could be applied to people that are active and anyone participating in strenuous activity.”

As for commercial applications, the researchers believe the device could be used as a training aid to monitor lactate changes in the same way that athletes use heart rate monitors to see how their heart rate changes during exercise.

On-body testing

The team is currently working to redesign the physical appearance of the patch to move from laboratory research to on-body tests. Once the scientists optimize how the sensor adheres to the skin, its sweat sample delivery/removal, and the systems electronic components, volunteers will test its capabilities while exercising.

“We had actually talked about this idea to some local high school football coaches,” Ulyanova says, “and they seem to really like it and are willing to put forth the use of their players to beta test the idea.”

After initial data is gathered, the team will be able to work with other groups to interpret the data and relate it to the physical condition of the person. With this, predictive models could be built to potentially help prevent conditions related to individual overexertion.

Future plans for the device include implementing wireless transmission of results and the development of a suite of sensors (a hybrid sensor) that can detect various other biomolecules, indicative of physical or physiological stressors.

Here’s a link to and a citation for the paper,

Wearable Sensor System Powered by a Biofuel Cell for Detection of Lactate Levels in Sweat by S. O. Garcia, Y. V. Ulyanova, R. Figueroa-Teran, K. H. Bhatt, S. Singhal and P. Atanassov. ECS J. Solid State Sci. Technol. 2016 volume 5, issue 8, M3075-M3081 doi: 10.1149/2.0131608jss

This paper is behind a paywall.

Wearable device to monitor and control diabetes is based on graphene

The research comes from Korea’s Institute of Basic Science and was announced in a March 22, 2016 news article by Lee Chi-dong for Yonhap News Agency,

A team of South Korean scientists announced Tuesday [March 22, 2016] that they have developed a wearable device, based on nanotechnology, for more convenient diabetes monitoring and therapy.

The graphene-using “smart patch” has improved the accuracy of blood sugar level measurements as it checks not only glucose in sweat but also temperature and acidity, according to the Institute for Basic Science (IBS) located in Daejeon, some 160 kilometers south of Seoul.

Existing smart patches gauge blood sugar merely in sweat.

Google is working on “smart contact lens” with an ultra-tiny super sensitive glucose sensor for tear fluid. Its accuracy remains a question amid concerns about adverse effects on eye health.

A March 21, 2016 IBS press release on EurekAlert provides more details about the work,

A scientific team from the Center for Nanoparticle Research at IBS has created a wearable GP [graphene]-based patch that allows accurate diabetes monitoring and feedback therapy by using human sweat. The researchers improved the device’s detecting capabilities by integrating electrochemically active and soft functional materials on the hybrid of gold-doped graphene and a serpentine-shape gold mesh. The device’s pH and temperature monitoring functions enable systematic corrections of sweat glucose measurements as the enzyme-based glucose sensor is affected by pH (blood acidity levels) and temperature.

Diabetes and regulating glucose levels

Insulin is produced in the pancreas and regulates the use of glucose, maintaining a balance in blood sugar levels. Diabetes causes an imbalance: insufficient amounts of insulin results in high blood glucose levels, known as hyperglycemia. Type 2 diabetes is the most common form of diabetes with no known cure. It affects some 3 million Koreans with the figure increasing due to dietary patterns and an aging society. The current treatments available to diabetics are painful, inconvenient and costly; regular visits to a doctor and home testing kits are needed to record glucose levels. Patients also have to inject uncomfortable insulin shots to regulate glucose levels. There is a significant need for non-invasive, painless, and stress-free monitoring of important markers of diabetes using multifunctional wearable devices. The IBS device facilitates this and thereby reduces the lengthy and expensive cycles of visiting doctors and pharmacies.

Components of the graphene-based wearable device

KIM Dae-Hyeong, a scientist from the Center for Nanoparticle Research, describes the vast array of components: “Our wearable GP-based device is capable of not only sweat-based glucose and pH monitoring but also controlled transcutaneous drug delivery through temperature-responsive microneedles. Precise measurement of sweat glucose concentrations are used to estimate the levels of glucose in the blood of a patient. The device retains its original sensitivity after multiple uses, thereby allowing for multiple treatments. The connection of the device to a portable/ wireless power supply and data transmission unit enables the point-of-care treatment of diabetes.” The professor went on to describe how the device works, “The patch is applied to the skin where sweat-based glucose monitoring begins on sweat generation. The humidity sensor monitors the increase in relative humidity (RH). It takes an average of 15 minutes for the sweat-uptake layer of the patch to collect sweat and reach a RH over 80% at which time glucose and pH measurements are initiated.”

Merits of the device and drug administration

The device shows dramatic advances over current treatment methods by allowing non-invasive treatments. During the team’s research, two healthy males participated in tests to demonstrate the sweat-based glucose sensing of the device. Glucose and pH levels of both subjects were recorded; a statistical analysis confirmed the reliable correlation between sweat glucose data from the diabetes patch and those from commercial glucose tests. If abnormally high levels of glucose are detected, a drug is released into a patient’s bloodstream via drug loaded microneedles. The malleable, semi-transparent skin-like appearance of the GP device provides easy and comfortable contact with human skin, allowing the sensors to remain unaffected by any skin deformations. This enables stable sensing and efficient drug delivery.

The scientific team also demonstrated the therapeutic effects by experimenting on diabetic (db/db) mice. Treatment began by applying the device near the abdomen of the db mouse. Microneedles pierced the skin of the mouse and released Metformin, an insulin regulating drug, into the bloodstream. The group treated with microneedles showed a significant suppression of blood glucose concentrations with respect to control groups. “One can easily replace the used microneedles with new ones. Treatment with Metformin through the skin is more efficient than that through the digestive system because the drug is directly introduced into metabolic circulation through the skin,” commented KIM Dae-Hyeong. He went on: “These advances using nanomaterials and devices provide new opportunities for the treatment of chronic diseases like diabetes.”

The researchers have made an image illustrating their work available,

Caption: Optical image of the GP-hybrid electrochemical device array on the human skin Credit: IBS

Caption: Optical image of the GP-hybrid electrochemical device array on the human skin Credit: IBS

Here’s a link to and a citation for the paper,

A graphene-based electrochemical device with thermoresponsive microneedles for diabetes monitoring and therapy by Hyunjae Lee, Tae Kyu Choi, Young Bum Lee, Hye Rim Cho, Roozbeh Ghaffari, Liu Wang, Hyung Jin Choi, Taek Dong Chung, Nanshu Lu, Taeghwan Hyeon, Seung Hong Choi, & Dae-Hyeong Kim. Nature Nanotechnology (2016) doi:10.1038/nnano.2016.38 Published online 21 March 2016

This paper is behind a paywall.

Touchless displays with 2D nanosheets and sweat

Swiping touchscreens with your finger has become a dominant means of accessing information in many applications but there is at least one problem associated with this action. From an Oct. 2, 2015 news item on phys.org,

While touchscreens are practical, touchless displays would be even more so. That’s because, despite touchscreens having enabled the smartphone’s advance into our lives and being essential for us to be able to use cash dispensers or ticket machines, they do have certain disadvantages. Touchscreens suffer from mechanical wear over time and are a transmission path for bacteria and viruses. To avoid these problems, scientists at Stuttgart’s Max Planck Institute for Solid State Research and LMU Munich have now developed nanostructures that change their electrical and even their optical properties as soon as a finger comes anywhere near them.

Here’s what a touchless screen looks like when tracking,

Touchless colour change: A nanostructure containing alternating layers of phosphatoantimonate nanosheets and oxide ... [more] © Advanced Materials 2015/MPI for Solid State Research

Touchless colour change: A nanostructure containing alternating layers of phosphatoantimonate nanosheets and oxide … [more]
© Advanced Materials 2015/MPI for Solid State Research

An Oct. 1, 2015 Max Planck Institute press release, which originated the news item, gives technical details,

A touchless display may be able to capitalize on a human trait which is of vital importance, although sometimes unwanted: This is the fact that our body sweats – and is constantly emitting water molecules through tiny pores in the skin. Scientists of the Nanochemistry group led by Bettina Lotsch at the Max Planck Institute for Solid State Research in Stuttgart and the LMU Munich have now been able to visualize the transpiration of a finger with a special moisture sensor which reacts as soon as an object – like an index finger – approaches its surface, without touching it. The increasing humidity is converted into an electrical signal or translated into a colour change, thus enabling it to be measured.

Phosphatoantimonic acid is what enables it to do this. This acid is a crystalline solid at room temperature with a structure made up of antimony, phosphorous, oxygen and hydrogen atoms. “It’s long been known to scientists that this material is able to take up water and swells considerably in the process,” explained Pirmin Ganter, doctoral student at the Max Planck Institute for Solid State Research and the Chemistry Department at LMU Munich. This water uptake also changes the properties of the material. For instance, its electrical conductivity increases as the number of stored water molecules rises. This is what enables it to serve as a measure of ambient moisture.

A sandwich nanomaterial structure exposed to moisture also changes its colour

However, the scientists aren’t so interested in developing a new moisture sensor. What they really want is to use it in touchless displays. “Because these sensors react in a very local manner to any increase in moisture, it is quite conceivable that this sort of material with moisture-dependent properties could also be used for touchless displays and monitors,” said Ganter. Touchless screens of this kind would require nothing more than a finger to get near the display to change their electrical or optical properties – and with them the input signal – at a specific point on the display.

Taking phosphatoantimonate nanosheets as their basis, the Stuttgart scientists then developed a photonic nanostructure which reacts to the moisture by changing colour. “If this was built into a monitor, the users would then receive visible feedback to  their finger motion” explained Katalin Szendrei, also a doctoral student in Bettina Lotsch’s group. To this end, the scientists created a multilayer sandwich material with alternating layers of ultrathin phosphatoantimonate nanosheets and silicon dioxide (SiO2) or titanium dioxide nanoparticles (TiO2). Comprising more than ten layers, the stack ultimately reached a height of little more than one millionth of a metre.

For one thing, the colour of the sandwich material can be set via the thickness of the layers. And for another, the colour of the sandwich changes if the scientists increase the relative humidity in the immediate surroundings of the material, for instance by moving a finger towards the screen. “The reason for this lies in the storage of water molecules between the phosphatoantimonate layers, which makes the layers swell considerably,” explained Katalin Szendrei. “A change in the thickness of the layers in this process is accompanied by a change in the colour of the sensor – produced in a similar way to what gives colour to a butterfly wing or in mother-of-pearl.”

The material reacts to the humidity change within a few milliseconds

This is a property that is fundamentally well known and characteristic of so-called photonic crystals. But scientists had never before observed such a large colour change as they now have in the lab in Stuttgart. “The colour of the nanostructure turns from blue to red when a finger gets near, for example. In this way, the colour can be tuned through the whole of the visible spectrum depending on the amount of water vapour taken up,” stressed Bettina Lotsch.

The scientists’ new approach is not only captivating because of the striking colour change. What’s also important is the fact that the material reacts to the change in humidity within a few milliseconds – literally in the blink of an eye. Previously reported materials normally took several seconds or more to respond. That is much too slow for practical applications. And there’s another thing that other materials couldn’t always do: The sandwich structure consisting of phosphatoantimonate nanosheets and oxide nanoparticles is highly stable from a chemical perspective and responds selectively to water vapour.

A layer protecting against chemical influences has to let moisture through

The scientists can imagine their materials being used in much more than just future generations of smartphones, tablets or notebooks. “Ultimately, we could see touchless displays also being deployed in many places where people currently have to touch monitors to navigate,” said Bettina Lotsch. For instance in cash dispensers or ticket machines, or even at the weighing scales in the supermarket’s vegetable aisle. Displays in public placesthat are used by many different people would have distinct hygiene benefits if they were touchless.

But before we see them being used in such places, the scientists have a few more challenges to overcome. It’s important, for example, that the nanostructures can be produced economically. To minimize wear, the structures still need to be coated with a protective layer if they’re going to be used in anything like a display. And that, again, has to meet not one but two different requirements: It must protect the moisture-sensitive layers against chemical and mechanical influences. And it must, of course, let the moisture pass through. But the Stuttgart scientists have an idea for how to achieve that already. An idea they are currently starting to put into practice with an additional cooperation partner on board.

Dexter Johnson’s Oct. 2, 2015 posting on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) provides some additional context for this research (Note: A link has been removed),

In a world where the “swipe” has become a dominant computer interface method along with moving and clicking the mouse, the question becomes what’s next? For researchers at Stuttgart’s Max Planck Institute for Solid State Research and LMU Munich, Germany, the answer continues to be a swipe, but one in which you don’t actually need to touch the screen with your finger. Researchers call these no-contact computer screens touchless positioning interfaces (TPI).

Here’s a link to and a citation for the paper,

Touchless Optical Finger Motion Tracking Based on 2D Nanosheets with Giant Moisture Responsiveness by Katalin Szendrei, Pirmin Ganter, Olalla Sànchez-Sobrado, Roland Eger, Alexander Kuhn, and Bettina V. Lotsch. Advanced Materials DOI: 10.1002/adma.201503463 Article first published online: 22 SEP 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

A ‘sweat’mometer—sensing your health through your sweat

At this point, it’s more fitness monitor than diagnostic tool, so, you’ll still need to submit blood, stool, and urine samples when the doctor requests it but the device does offer some tantalizing possibilities according to a May 15, 2015 news item on phys.org,

Made from state-of-the-art silicon transistors, an ultra-low power sensor enables real-time scanning of the contents of liquids such as perspiration. Compatible with advanced electronics, this technology boasts exceptional accuracy – enough to manufacture mobile sensors that monitor health.

Imagine that it is possible, through a tiny adhesive electronic stamp attached to the arm, to know in real time one’s level of hydration, stress or fatigue while jogging. A new sensor developed at the Nanoelectronic Devices Laboratory (Nanolab) at EPFL [École Polytechnique Fédérale de Lausanne in Switzerland] is the first step toward this application. “The ionic equilibrium in a person’s sweat could provide significant information on the state of his health,” says Adrian Ionescu, director of Nanolab. “Our technology detects the presence of elementary charged particles in ultra-small concentrations such as ions and protons, which reflects not only the pH balance of sweat but also more complex hydration of fatigues states. By an adapted functionalization I can also track different kinds of proteins.”

A May 15, 2015 EPFL press release by Laure-Anne Pessina, which originated the news item, includes a good technical explanation of the device for non-experts in the field,

Published in the journal ACS Nano, the device is based on transistors that are comparable to those used by the company Intel in advanced microprocessors. On the state-of-the-art “FinFET” transistor, researchers fixed a microfluidic channel through which the fluid to be analyzed flows. When the molecules pass, their electrical charge disturbs the sensor, which makes it possible to deduce the fluid’s composition.

The new device doesn’t host only sensors, but also transistors and circuits enabling the amplification of the signals – a significant innovation. The feat relies on a layered design that isolates the electronic part from the liquid substance. “Usually it is necessary to use separately a sensor for detection and a circuit for computing and signal amplification,” says Sara Rigante, lead author of the publication. “In our chip, sensors and circuits are in the same device – making it a ‘Sensing integrated circuit’. This proximity ensures that the signal is not disturbed or altered. We can thereby obtain extremely stable and accurate measurements.”

But that’s not all. Due to the size of the transistors – 20 nanometers, which is one hundred to one thousand times smaller than the thickness of a hair – it is possible to place a whole network of sensors on one chip, with each sensor locating a different particle. “We could also detect calcium, sodium or potassium in sweat,” the researcher elaborates.

As to what makes the device special (from the press release),

The technology developed at EPFL stands out from its competitors because it is extremely stable, compatible with existing electronics (CMOS), ultra-low power and easy to reproduce in large arrays of sensors. “In the field of biosensors, research around nanotechnology is intense, particularly regarding silicon nanowires and nanotubes. But these technologies are frequently unstable and therefore unusable for now in industrial applications,” says Ionescu. “In the case of our sensor, we started from extremely powerful, advanced technology and adapted it for sensing need in a liquid-gate FinFET configurations. The precision of the electronics is such that it is easy to clone our device in millions with identical characteristics.”

In addition, the technology is not energy intensive. “We could feed 10,000 sensors with a single solar cell,” Professor Ionescu asserts.

Of course, there does seem to be one shortcoming (from the press release),

Thus far, the tests have been carried out by circulating the liquid with a tiny pump. Researchers are currently working on a means of sucking the sweat into the microfluidic tube via wicking. This would rid the small analyzing “band-aid” of the need for an attached pump.

While they work on eliminating the pump part of the device, here’s  a link to and a citation for the paper,

Sensing with Advanced Computing Technology: Fin Field-Effect Transistors with High-k Gate Stack on Bulk Silicon by Sara Rigante, Paolo Scarbolo, Mathias Wipf, Ralph L. Stoop, Kristine Bedner, Elizabeth Buitrago, Antonios Bazigos, Didier Bouvet, Michel Calame, Christian Schönenberger, and Adrian M. Ionescu. ACS Nano, Article ASAP DOI: 10.1021/nn5064216 Publication Date (Web): March 27, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

As for the ‘sweat’mometer in the headline, I was combining sweat with thermometer.

A tattoo that’s a biobattery and a sensor?

It’s going to be an American Chemical Society (ACS) 248th meeting kind of week as yet another interesting piece of scientific research is bruited (spread) about the internet. This time it’s all about sweat, exercise, and biobatteries. From an Aug. 13, 2014 news item on Nanowerk,

In the future, working up a sweat by exercising may not only be good for your health, but it could also power your small electronic devices. Researchers will report today that they have designed a sensor in the form of a temporary tattoo that can both monitor a person’s progress during exercise and produce power from their perspiration.

An Aug. 13, 2014 ACS news release on EurekAlert, which originated the news item, describes the inspiration (as opposed to perspiration) for this technology,

The device works by detecting and responding to lactate, which is naturally present in sweat. “Lactate is a very important indicator of how you are doing during exercise,” says Wenzhao Jia, Ph.D.

In general, the more intense the exercise, the more lactate the body produces. During strenuous physical activity, the body needs to generate more energy, so it activates a process called glycolysis. Glycolysis produces energy and lactate, the latter of which scientists can detect in the blood.

Professional athletes monitor their lactate levels during performance testing as a way to evaluate their fitness and training program. In addition, doctors measure lactate during exercise testing of patients for conditions marked by abnormally high lactate levels, such as heart or lung disease. Currently, lactate testing is inconvenient and intrusive because blood samples must be collected from the person at different times during the exercise regime and then analyzed.

The news release goes on to describe the research process which resulted in a temporary tattoo that could be used to power small scale electronics,

Jia, a postdoctoral student in the lab of Joseph Wang, D.Sc., at the University of California San Diego, and her colleagues developed a faster, easier and more comfortable way to measure lactate during exercise. They imprinted a flexible lactate sensor onto temporary tattoo paper. The sensor contained an enzyme that strips electrons from lactate, generating a weak electrical current. The researchers applied the tattoo to the upper arms of 10 healthy volunteers. Then the team measured the electrical current produced as the volunteers exercised at increasing resistance levels on a stationary bicycle for 30 minutes. In this way, they could continuously monitor sweat lactate levels over time and with changes in exercise intensity.

The team then went a step further, building on these findings to make a sweat-powered biobattery. Batteries produce energy by passing current, in the form of electrons, from an anode to a cathode. In this case, the anode contained the enzyme that removes electrons from lactate, and the cathode contained a molecule that accepts the electrons.

When 15 volunteers wore the tattoo biobatteries while exercising on a stationary bike, they produced different amounts of power. Interestingly, people who were less fit (exercising fewer than once a week) produced more power than those who were moderately fit (exercising one to three times per week). Enthusiasts who worked out more than three times per week produced the least amount of power. The researchers say that this is probably because the less-fit people became fatigued sooner, causing glycolysis to kick in earlier, forming more lactate. The maximum amount of energy produced by a person in the low-fitness group was 70 microWatts per cm2 of skin.

“The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices,” Jia says. “Right now, we can get a maximum of 70 microWatts per cm2, but our electrodes are only 2 by 3 millimeters in size and generate about 4 microWatts — a bit small to generate enough power to run a watch, for example, which requires at least 10 microWatts. So besides working to get higher power, we also need to leverage electronics to store the generated current and make it sufficient for these requirements.”

Biobatteries offer certain advantages over conventional batteries: They recharge more quickly, use renewable energy sources (in this case, sweat), and are safer because they do not explode or leak toxic chemicals.

“These represent the first examples of epidermal electrochemical biosensing and biofuel cells that could potentially be used for a wide range of future applications,” Wang says.

The ACS has made a video about this work available,

It seems to me this tattoo battery could be used as a self-powered monitoring device in a medical application for heart or lung disease.

Blood, memristors, cyborgs plus brain-controlled computers, prosthetics, and art

The memristor, a circuit element that quite interests me [April 7, 2010 posting], seems to be moving from being a purely electrical engineering term to one that’s used metaphorically to describe biological processes in a way that is transforming my understanding of machine/human (and other animal) interfaces from a science fiction concept to reality.

March 2, 2011 Kate McAlpine wrote an article for the New Scientist which suggested that skin has memristive properties while noting that the same has been said of the brain. From Sweat ducts make skin a memristor,

Synapses, junctions between neurons in the brain, display electrical behaviour that depends on past activity and are said to behave like memristors. This has raised the prospect of using memristors as the basis of an artificial brain.

Now, by re-examining data from the early 1980s on the electrical conductivity of human skin in response to various voltages, Gorm Johnsen and his colleagues at the University of Oslo in Norway have uncovered a more prosaic example of memristive behaviour in nature.

They found that when a negative electrical potential is applied to skin on various parts of the arm, creating a current, that stretch of skin exhibits a low resistance to a subsequent current flowing through the skin. But if the first potential is positive relative to the skin, then a subsequent potential produces a current that meets with a much higher resistance. In other words, the skin has a memory of previous currents. The finding is due to be published in Physical Review E.
The researchers attribute skin’s memristor behaviour to sweat pores.

More recently, there’s been some excitement about a research team in India that’s working with blood so they can eventually create a ‘liquid memristor’. Rachel Courtland wrote a brief item on the ‘blood memristor’ on April 1, 2011 for the IEEE Tech Talk blog,

S.P. Kosta of the Education Campus Changa in Gujarat, India and colleagues have published a paper in the International Journal of Medical Engineering and Informatics showing that human blood changes its electrical resistance depending on how much voltage is applied. It also seems to retain memory of this resistance for at least five minutes.

The team says that makes human blood a memristor: the fourth in the family of fundamental circuit elements that includes the resistor, the capacitor, and the inductor. Proposed in 1971, the memristor’s existence wasn’t proven until 2008, when HP senior fellow Stanley Williams and colleagues demonstrated a memristor device made of doped titanium dioxide.

There was also a March 30, 2011 news item about the Indian research titled, Blood simple circuitry for cyborgs, on Nanowerk, which provided this information,

They [the research team] constructed the laboratory-based biological memristor using a 10 ml test tube filled with human blood held at 37 Celsius into which two electrodes are inserted; appropriate measuring instrumentation was attached. The experimental memristor shows that resistance varies with applied voltage polarity and magnitude and this memory effect is sustained for at least five minutes in the device.

Having demonstrated memristor behavior in blood, the next step was to test that the same behavior would be observed in a device through which blood is flowing. This step was also successful. The next stage will be to develop a micro-channel version of the flow memristor device and to integrate several to carry out particular logic functions. This research is still a long way from an electronic to biological interface, but bodes well for the development of such devices in the future.

Kit Eaton in an April 4, 2011 article (Electronics Made from Human Blood Cells Suggest Cyborg Interfaces, Spark Nightmares) on the Fast Company website gives more details about possible future applications,

Ultimately, the fact that a biological system could be used to interact with a hard semiconductor system could revolutionize biomechanics. That’s because wiring devices like cochlear implants, nerve-triggered artificial limbs and artificial eyeballs into the body at the moment involves a terribly difficult integration of metal wiring–with all the associated risk of infection and rejection. Plus it’s really a very promising first step toward making a cyborg. Countdown to military interest in this tech in 5…4…3…

It should be noted that the team in India is working towards applications in neuroprosthetics. As for the Norwegian team with their ‘sweat duct/skin memristor’, the article did not specify what types of applications, if any, their work might lead to.

As evidenced by the research covered in these news items, the memristor seems to be drifting or, more accurately, developing a second identity/ghost identity as the term is applied to biological processes.

The body as a machine is a notion that’s been around for a while as has the notion of combining the two. The first notion is a metaphor while the second is a staple in science fiction which, in a minor way, has found a home in the real life practice of body hacking where someone implants a magnetic or computer chip into their body (my May 27, 2010 posting). So the memristor becoming a metaphor for certain biological processes doesn’t seem something new but rather the next step in a process that’s well on its way.

Two students at Ryerson University (Toronto, Canada) recently announced that they had developed a brain-controlled prosthetic. From the March 30, 2011 news item on Nanowerk,

Two Ryerson University undergraduate biomedical engineering students are changing the world of medical prosthetics with a newly developed prosthetic arm that is controlled by brain signals. The Artificial Muscle-Operated (AMO) Arm not only enables amputees more range of movement as compared to other prosthetic arms but it allows amputees to avoid invasive surgeries and could potentially save hundreds of thousands of dollars. The AMO Arm is controlled by the user’s brain signals and is powered by ‘artificial muscles’ – simple pneumatic pumps and valves – to create movements. In contrast, traditional prosthetic limbs – which typically offer more limited movements – rely on intricate and expensive electrical and mechanical components.

Developed by third-year student Thiago Caires and second-year student Michal Prywata, the AMO Arm is controlled by the brain and uses compressed air as the main source of power. The digital device makes use of signals in the brain that continue to fire even after a limb is amputated. Users wear a head-set that senses a signal – for example, the thought “up” – and sends it wirelessly to a miniature computer in the arm. The computer then compares the signal to others in a database. The resulting information is sent to the pneumatic system, which in turn, activates the arm to create the correct movement. Simulating the expansion and contraction of real muscles, the system makes use of compressed air from a small, refillable tank in the user’s pocket.

I think what they mean is that the components are not traditionally electrical and mechanical but in fact informed by emerging technologies and the science that supports them. After all, the computer must run on some kind of electricity and brain activity (wireless signals from the brain will be controlling the prosthetic) is often described as electrical. The result is that the human and the machine are effectively made one since the prosthetic arm is controlled as if it were ‘biological’ arm.

On another part of the spectrum, Iraqui artist Wafaa Bilal made headlines recently when he had a camera implanted into the back of his head creating a third eye. Designed to be a one year project, the artist had to remove the camera when he developed an infection at the site of one of the metal posts used to anchor the camera to his head. From the Feb. 11, 2011 BBC news item,

An artist who had a camera implanted into the back of his head has been forced to remove it after his body rejected part of the device.

Iraqi-born Wafaa Bilal had surgery last week to remove one of three posts holding the camera in place as it posed a risk of infection.

The camera had been taking a photo every minute as part of a year-long project.

Wafaa Bilal and camera (image downloaded from BBC website)

(The artist would like to try it again but, in the meantime, has slung the camera around his neck as a substitute.)

In Bilal’s case, the body is being significantly altered as the machine (camera) is implanted in a place (back of head) where no animal has them located.

What I’m getting at with all of this is that at the same time we seem to be expanding the memristor’s meaning from a term used to describe a concept in electrical engineering to include biological processes, we are exploring new ways of integrating machinery into our bodies. In effect our relationships to our bodies and machines are changing and that change can be traced in the language we use to describe ourselves.
 

Sweating out silver nanoparticles

I’ve often wondered if the  silver nanoparticles, which coat the textiles used for clothing that doesn’t smell or need to be cleaned often, gets washed off by your sweat. As Michael Berger noted in his November 4, 2009 article on Nanowerk, researchers have found that silver nanoparticles do get washed off into the water,

Researchers in Switzerland have now examined what happens to these silver nanoparticle-treated textiles during washing. The scientists studied release of nanoparticles in laundry water from nine different textiles, including different brands of commercially available anti-odor socks. Studies like these will help address the question what the chances are of nanoparticles from nanofinished textiles being released into the environment.

“We found that the total released varied considerably from less than 1 to 45 percent of the total nanosilver in the fabric and that most came out during the first wash,” Bernd Nowack, head of the Environmental Risk Assessment and Management Group at the Empa-Swiss Federal Laboratories for Materials Testing and Research, tells Nanowerk. “These results have important implications for the risk assessment of silver textiles and also for environmental fate studies of nanosilver, because they show that under certain conditions relevant to washing, primarily coarse silver-containing particles are released.”

As it turns out, Thai researchers have recently discovered that sweat will also wash off those silver nanoparticles (from the news item on Nanowerk),

A recent study by researchers at National Nanotechnology Center (NANOTEC) in Thailand has provided the data on detecting silver released from antibacterial fabric products using artificial sweat as a model to represent the human skin environment.

“The amount of silver released from fabrics into artificial sweat was dependent upon the initial amount of silver coating, the fabric quality, pH and artificial sweat formulations “said Dr Rawiwan Maniratanachote, head of Nano Safety and Risk Assessment Lab. “The study could be useful to evaluate potential human risk when exposed to silver nanoparticles from textile materials.”

I guess the next couple of questions to be answered are: do the silver nanoparticles being washing off by your sweat penetrate your skin and/or do the silver nanoparticles wash off your skin and into the water supply?