Graphene-Based Tattoo Functions as Wearable Electronic Device

Researchers have designed a graphene-based tattoo that can be directly laminated onto the skin with water, similar to a temporary tattoo. But instead of featuring artistic or colorful designs, the new tattoo is nearly transparent.

The graphene tattoos retain their full function for about two days, but can be peeled off by a piece of adhesive tape if desired. (Credit: Shideh Kabiri Ameri et al. 2017 American Chemical Society)

Its main attraction is that graphene’s unique electronic properties enable the tattoo to function as a wearable electronic device, with potential applications including biometric uses (such as measuring the electrical activity of the heart, brain, and muscles), as well as human-machine interactions.

The researchers, led by Deji Akinwande and Nanshu Lu at the University of Texas at Austin, have published a paper on the new graphene electronic  in a recent issue of ACS Nano.

In some ways, the graphene electronic tattoo is similar to commercially available electronic devices for health and fitness tracking: both kinds of devices are capable of heart rate monitoring and bioimpedence (a measure of the body’s response to an electric current). But because the ultrathin graphene tattoos can fully conform to the , they offer medical-grade data quality, in contrast with the lower performance of the rigid electrode sensors mounted on bands and strapped to the wrist or chest. Due to the high-quality sensing, the researchers expect that the graphene tattoos may offer promising replacements for existing medical sensors, which are typically taped to the skin and require gel or paste to enable the electrodes to function.

“The graphene tattoo is a dry physiological sensor which, because of its thinness, forms an ultra-conformal contact to skin, resulting in increased signal fidelity,” coauthor Shideh Kabiri Ameri at the University of Texas at Austin told “Conformability results in less susceptibility to motion artifacts, which is one the biggest drawbacks of conventional dry sensors and electrodes for physiological measurements.”

The new tattoos are made of graphene that is coated with an ultrathin backing layer of transparent polymer poly(methyl methacrylate) (PMMA). During fabrication, the graphene/PMMA bilayer is transferred to a piece of ordinary tattoo paper, and the bilayer is then carved into different patterns of serpentine ribbons to make different types of sensors. The finished tattoo is then transferred to any part of the body by bringing the graphene side in contact with the skin and applying water to the back of the tattoo paper to release the tattoo. The tattoos retain their full function for around two days or more, but can be peeled off by a piece of adhesive tape if desired.

Since the researchers previously showed that, theoretically, a graphene tattoo must be less than 510 nm thick to fully conform to human skin and exhibit optimal performance, the tattoo they fabricated here is just 460 nm thick. Combined with graphene/PMMA bilayer optical transparency of approximately 85%, and the fact that the tattoos are more stretchable than human skin, the resulting graphene tattoos are barely perceptible, both mechanically and optically.

Tests showed that the graphene electronic tattoos can be successfully used to measure a variety of electrophysiological signals, including skin temperature and skin hydration, and can function as an electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG) for measuring the electrical activity of the heart, muscles, and brain, respectively.

“Graphene electronic tattoos are most promising for potential applications in mobile health care, assisted technologies, and ,” Kabiri Ameri said. “In the area of human machine interfaces, electrophysiological signals recorded from the brain and muscles can be classified and assigned for specific action in a machine. This area of research can have applications for the internet of things, smart houses and cities, human computer interaction, smart wheelchairs, speech assistance technology, monitoring of distracted driving, and human-robot control. Recently we have demonstrated the application of  tattoos for sensing human signals to wirelessly control flying objects. That demonstration will be reported in the near future.”

Graphene Nanocomposite to Improve Desalination Processes

The use of reverse osmosis desalination technology has gathered more and more usage and interest over the last few years. It is responsible for producing a large amount of fresh water for the growing populations around the world.

Despite their widespread usage, there are still fundamental issues that need to be addressed, and in an effort to expand this technology to more desalination plants worldwide, a team of Researchers from Australia and Egypt have created a new thin film nano-composite (TFNC) membrane to address the issues surrounding water flux, salt rejection and biofouling in these processes.

Currently, reverse osmosis (RO) desalination technology is used in more than 50% of the world’s desalination plants for the production of fresh water. Within these technologies, thin-film composite (TFC) membranes are the most common material utilized for nanofiltration processes.

However, even though this technology is used across most of our drinking water purification processes, they are still privy to some drawbacks, namely a trade-off between both water flux and salt rejection, chlorine degradation and biofouling- all of which lead to the loss of membrane flux and salt rejection performance.

Biofouling is currently the biggest challenge facing desalination plants. Biofouling in these desalination processes has been linked to microorganisms that attach themselves to the filter membrane, where the membrane(ligand)-organism(receptor) interactions cause the formation of extracellular polymeric substances which increase the adherence of bacteria to the membrane.

To combat this, the Researchers required a material with a large (and smooth) surface area for filtering processes, which also possessed biocidal properties.

Naturally, a derivative of graphene is the obvious choice and the Researchers decided upon graphene oxide (GO) nanosheets that help improve the flux, selectivity and antibacterial properties of TFNC membranes.

The Researchers created the composite by incorporating the graphene oxide nanosheets into a thin polyamide (PA) active layer, in the form of poly tannic acid-functionalized graphene oxide nanosheets (pTA-f-GO).

The layers were produced through interfacial polymerization. The graphene oxide was first functionalized with tannic acid (TA) followed by polyethyleneimine (PEI). The tannic acid groups were found to bind tightly to the graphene oxide surface whilst the PEI groups provided free amine groups which helped to facilitate crosslinking to both the tannic acid groups and the polyamide active layer.

The crosslinking chains were found to interact very strongly with the graphene oxide sheets and tightly integrate them into the nanocomposite matrix.

The Researchers characterized the new TNFC using Transmission electron microscopy (TEM, FEI Tecnai G2 Spirit), atomic force microscopy (AFM, NT-MDT NTEGRA SPM), Fourier-transform infrared spectroscopy (FTIR, Nicolet Nexus 8700 FTIR Spectrophotometer, Thermo Electron Corporation) with a smart orbit attenuated total reflectance probe, X-ray photoelectron spectroscopy (XPS, Kratos Axis-Ultra DLD, Kratos Analytical) with CasaXPS software (Neal Fairly), electrokinetic analysis methods (Anton Paar) and captive bubble techniques.

By incorporating the pTA-f-GO layer into the TFNC membranes, the Researchers achieved a filtration material with a thinner PA layer, lower surface roughness and a higher hydrophobicity. The presence of such properties increased both the membrane water flux by up to 40% and the salt rejection by 8%.

In addition, the biocidal properties of the graphene sheet within the active layer improved the antibacterial properties of the membrane by 80% compared to standard non-composite membranes.

The process of fabrication was also found to be practical, scalable, versatile, of lower energy consumption, have an improved performance and possess an increased cost-efficiency against current methods. Such production benefits lend the nanocomposite membranes to be implemented across a wide range of applications.

Couple this with the TFNC’s excellent separation and anti-biofouling properties, and the material is one that could easily see itself become a commercially used membrane in the near future, and will perhaps help to increase the number of desalination plants around the world which use of reverse osmosis desalination methods.

Human pheromones

The existence of human pheromones remains controversial. It’s clear that many plants and animals species use hormonal secretions to communicate information relating to reproduction. For example, in 1959 researchers discovered that female silkworms secreted a powerful aphrodisiac, called bombykol, that can attract male silkworms from miles away. To date, however, ironclad evidence that human behavior is governed by pheromones remains elusive.

Nevertheless, there are a number of intriguing studies, which suggest the surprising ways that scents, secretions and body odors containing pheromones may influence human behavior unconsciously.

Unconscious communicationAccording to Bettina Pause, a psychologist, “We’ve just started to understand that there is communication below the level of consciousness. My guess is that a lot of our communication is influenced by chemosignals.”

Scientists explain that pheromones in animals are released in sweat, urine and saliva. These chemical messengers appear to have both an emotional and physical effect on other members of their species.

In mammals, for instance, pheromones are detected by a structure in the nose called the vomeronasal organ, which relays signals to the hypothalamus a region of the brain that controls emotional states, hormonal regulation and sexual arousal.

Some of the most important evidence for the existence of human pheromones comes from a 1998 study by Dr. Martha McClintock, who found that women who live in close proximity (the same dorm, for example) tend to have synchronized menstrual cycles. Scientists believe that chemical messages in sweat are responsible for this harmonization of periods.

Pheromones and brain imagingResearchers have found that certain smells activate the part of the brain related to sexuality.

One powerful form of evidence that pheromones exist comes from PET scanning technology, which can examine the effect of chemical odors on male and female brains. In one study, researchers found that certain hormone-like smells activated specific areas in the hypothalamus related to sexuality, which are not triggered by other odors.

In the words of Dr. David Berliner, “These findings corroborate that human pheromones do exist, and that women can communicate chemically with men and vice versa. This is a very important finding because it shows specific areas of the brain that are activated by these chemicals.”

As you might expect, the brains of heterosexual men and women respond very differently to specific chemical messengers. For example, the brain regions in the female hypothalamus are highly active when women are exposed to testosterone-like chemicals (while exposure to estrogen-like messengers has no effect). Conversely, the brain areas in the male hypothalami light up like a Christmas tree when men are exposed to estrogen-like hormones.

Scientists believe this gender-specific response to chemical secretions shapes the way men and women to perceive each other on an unconscious level.

Can pheromones make you more attractive?

If pheromones govern sexual arousal, then can they be harnessed to make people more attractive? More specifically, could pheromones be added to perfumes, which could be used to lure desired mates?

One study from the University of Chicago found that pheromone-type chemical can heighten the heart rate, increase body temperature and change mood. As of yet, however, scientists have been unable to isolate the specific chemicals that trigger attraction and sexual desire.

Of course, many perfume manufacturers claim that their fragrances can spark desire. In fact, most of these products contain pheromones from animals. However, most scientists insist that pheromones are species specific. In other words, until researchers can isolate specific human pheromones or develop synthetic analogs, then a true love potion of love will remain elusive.

Nevertheless, scientists are continuing to investigate pheromones for their scientific, commercial and therapeutic potential. For example, a company called Pherin Pharmaceuticals is looking into ways to use pheromones messengers to alleviate stress, anxiety and menstrual cramps.

How pheromones may influence human behavior

  • The odors breastfeeding women emit from their nipples attracts infants and primes women without children to be more sexually aroused.
  • A compound derived from testosterone (called androstadienone) has been shown to make women feel more relaxed.
  • Scientists are investigating something called the histocompatibility complex. This refers to a genetically-based “odor print,” which involves scents that reflect certain characteristics found in the genes and the immune system.
  • According to the olfactory neuroscientist Charles Wysocki, “With the exception of identical twins, no two individuals are likely to have the same odor print.”

Research by Wysocki and others indicates that women prefer the musky scent of men who happen to have gene characteristics that match up well with their own DNA. In other words, the nose knows. That is, odor prints may be a huge driver of attractiveness in so far as they help people pick mates with DNA that complements their own. This unconscious form of selection benefits offspring.

Love is in the air

Scientists are still a long way off from unraveling the mysteries of attraction and the role that pheromones may play in influencing sexual behavior. For centuries, people have used expressions like “love is in the air” and “love is a matter of chemistry.” The emerging science of pheromones suggests that these proverbial adages may be far truer than anyone imagined.