E-Skin transmits Glucose Concentrations, Blood Pressure, Heart Rate, to Your Smartphone

Wearable sensors are ubiquitous thanks to wireless technology that enables a person’s glucose concentrations, blood pressure, heart rate, and activity levels to be transmitted seamlessly from sensor to smartphone for further analysis. Most wireless sensors today communicate via embedded Bluetooth chips that are themselves powered by small batteries. But these conventional chips and power sources will likely be too bulky for next-generation sensors, which are taking on smaller, thinner, more flexible forms.

Now MIT engineers have devised a new kind of wearable sensor that communicates wirelessly without requiring onboard chips or batteries. Their design, detailed today in the journal Science, opens a path toward chip-free wireless sensors. The team’s sensor design is a form of electronic skin, or “e-skin” — a flexible, semiconducting film that conforms to the skin like electronic Scotch tape. The heart of the sensor is an ultrathin, high-quality film of gallium nitride, a material that is known for its piezoelectric properties, meaning that it can both produce an electrical signal in response to mechanical strain and mechanically vibrate in response to an electrical impulse. The researchers found they could harness gallium nitride’s two-way piezoelectric properties and use the material simultaneously for both sensing and wireless communication.

In their new study, the team produced pure, single-crystalline samples of gallium nitride, which they paired with a conducting layer of gold to boost any incoming or outgoing electrical signal. They showed that the device was sensitive enough to vibrate in response to a person’s heartbeat, as well as the salt in their sweat, and that the material’s vibrations generated an electrical signal that could be read by a nearby receiver. In this way, the device was able to wirelessly transmit sensing information, without the need for a chip or battery.

Chips require a lot of power, but our device could make a system very light without having any chips that are power-hungry,” says the study’s corresponding author, Jeehwan Kim, an associate professor of mechanical engineering and of materials science, and a principal investigator in the Research Laboratory of Electronics. “You could put it on your body like a bandage, and paired with a wireless reader on your cellphone, you could wirelessly monitor your pulse, sweat, and other biological signals.”

Jeehwan Kim’s group previously developed a technique, called remote epitaxy, that they have employed to quickly grow and peel away ultrathin, high-quality semiconductors from wafers coated with graphene. Using this technique, they have fabricated and explored various flexible, multifunctional electronic films. In their new study, the engineers used the same technique to peel away ultrathin single-crystalline films of gallium nitride, which in its pure, defect-free form is a highly sensitive piezoelectric material.

The team looked to use a pure film of gallium nitride as both a sensor and a wireless communicator of surface acoustic waves, which are essentially vibrations across the films. The patterns of these waves can indicate a person’s heart rate, or even more subtly, the presence of certain compounds on the skin, such as salt in sweat.

Source: https://news.mit.edu/

How to Produce Drinkable Water from Sea Water

University of California, Berkeley, chemists have discovered a way to simplify the removal of toxic metals, like mercury and boron, during desalination to produce clean water, while at the same time potentially capturing valuable metals, such as gold.

Desalination — the removal of salt — is only one step in the process of producing drinkable water, or water for agriculture or industry, from ocean or waste water. Either before or after the removal of salt, the water often has to be treated to remove boron, which is toxic to plants, and heavy metals like arsenic and mercury, which are toxic to humans. Often, the process leaves behind a toxic brine that can be difficult to dispose of.

The new technique, which can easily be added to current membrane-based electrodialysis desalination processes, removes nearly 100% of these toxic metals, producing a pure brine along with pure water and isolating the valuable metals for later use or disposal.

A flexible polymer membrane incorporating nanoparticles of PAF selectively absorbs nearly 100% of metals such mercury, copper or iron during desalination, more efficiently producing clean, safe water

Desalination or water treatment plants typically require a long series of high-cost, pre- and post-treatment systems that all the water has to go through, one by one,” said Adam Uliana, a UC Berkeley graduate student who is first author of a paper describing the technology. “But here, we have the ability to do several of these steps all in one, which is a more efficient process. Basically, you could implement it in existing setups.”

The UC Berkeley chemists synthesized flexible polymer membranes, like those currently used in membrane separation processes, but embedded nanoparticles that can be tuned to absorb specific metal ionsgold or uranium ions, for example. The membrane can incorporate a single type of tuned nanoparticle, if the metal is to be recovered, or several different types, each tuned to absorb a different metal or ionic compound, if multiple contaminants need to be removed in one step.

The polymer membrane laced with nanoparticles is very stable in water and at high heat, which is not true of many other types of absorbers, including most metal-organic frameworks (MOFs), when embedded in membranes.

Source: https://news.berkeley.edu/

How To Bring Fresh Water To Remote Communities

Researchers at the University of Bath (UK) have developed a revolutionary desalination process that has the potential to be operated in mobile, solar-powered units. The process is low cost, low energy and low maintenance, and has the potential to provide safe water to communities in remote and disaster-struck areas where fresh water is in short supply.

Developed by the university’s Water Innovation and Research Centre in partnership with Indonesia’s Bogor Agricultural University and the University of Johannesburg, the prototype desalination unit is a 3D-printed system with two internal chambers designed to extract and/or accumulate salt. When power is applied, salt cations (positively charged ions) and salt anions (negatively charged ions) flow between chambers through arrays of micro-holes in a thin synthetic membrane. The flow can only happen in one direction thanks to a mechanism that has parallels in mobile-phone technology. As a result of this one-way flow, salt is pumped out of seawater. This contrasts with the classical desalination process, where water rather than salt is pumped through a membrane.

Desalination, which turns seawater into fresh water, has become an essential process for providing drinking and irrigation water where freshwater is scarce. Traditionally, it has been an energy-intensive process carried out in large industrial plants.

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There are times when it would be enormously beneficial to install small, solar-powered desalination units to service a small number of households. Large industrial water plants are essential to 21st Century living, but they are of no help when you’re living in a remote location where drinking water is scarce, or where there is a coastal catastrophe that wipes out the fresh water supply,” said Professor Frank Marken from the Department of Chemistry

The Bath desalination system is based on ‘ionics’, where a cationic diode (a negatively charged, semi-permeable membrane studded with microscopic pores) is combined with an anionic resistor (a device that only allows the flow of negative ions when power is applied).

This amounts to a whole new process for removing salt from water,”explained Prof Marken. “We are the first people to use tiny micron-sized diodes in a desalination prototype.

He added: “This is a low-energy system with no moving parts. Other systems use enormous pressures to push the water through nano-pores, but we only remove the salts. Most intriguingly, the external pumps and switches can be replaced by microscopic processes inside the membrane – a little bit like biological membranes work.”

Source: https://www.bath.ac.uk/

A Pinch Of Salt Improves Drastically Battery Performance

Researchers at Queen Mary University of London, University of Cambridge and Max Planck Institute for Solid State Research have discovered how a pinch of salt can be used to drastically improve the performance of batteries. Surprisingly, the salt reacted with the sponge in special ways and turned it from a homogeneous mass to an intricate structure with fibres, struts, pillars and webs. This kind of 3D hierarchically organised carbon structure has proven very difficult to grow in a laboratory but is crucial in providing unimpeded ion transport to active sites in a battery. In the study, published in JACS (Journal of the American Chemical Society), the researchers demonstrate that the use of these materials in Lithium-ion batteries not only enables the batteries to be charged-up rapidly, but also at one of the highest capacities.

Due to their intricate architecture the researchers have termed these structures ‘nano-diatoms’, and believe they could also be used in energy storage and conversion, for example as electrocatalysts for hydrogen production.

This metamorphosis only happens when we heat the compounds to 800 degrees centigrade and was as unexpected as hatching fire-born dragons instead of getting baked eggs in the Game of Thrones. It is very satisfying that after the initial surprise, we have also discovered how to control the transformations with chemical composition,” said lead author Dr Stoyan Smoukov, from Queen Mary’s School of Engineering and Materials Science.

Source: https://www.qmul.ac.uk/