Graphene patch could help patients manage diabetes

A wearable, graphene-based patch could one day maintain healthy blood glucose levels in people by measuring the sugar in sweat and then delivering the necessary dose of a diabetes drug through the skin (Nat. Nanotech. 2016, DOI:10.1038/nnano.2016.38).

The device takes scientists a step closer to the “coveted prize” in diabetes care: a noninvasive method to monitor and control blood glucose levels, writes Richard Guyof the University of Bath in a commentary about the new work.

Currently, most diabetic patients keep track of their blood glucose levels by pricking their fingers and testing a resulting droplet of blood. For people who must monitor their levels regularly, this can be a literal pain. “There are a lot of people who don’t like sticking things in their skin,” Guy says.

About 15 years ago, the Food & Drug Administration approved a noninvasive glucose-monitoring device called the GlucoWatch Biographer. Patients wore it on their wrists, and it extracted glucose from interstitial fluid in the skin using a small current. It didn’t catch on, in part because it wasn’t user friendly, Guy tells C&EN.

For the new patch, the researchers, led by Dae-Hyeong Kim of Seoul National University, decided to detect glucose in sweat because previous studies had shown that levels of the sugar in perspiration match those in blood. Other groups have also developed devices that can analyze biomolecules in sweat (C&EN, Feb. 1, 2016, page 11).

The new device uses layers of the fluoropolymer Nafion to absorb sweat and carry it toward the device’s sensors, which are built on modified graphene. The team doped the graphene with gold atoms and functionalized it with electrochemically active materials to enable reactions needed to detect glucose.

In the patch’s glucose sensors, the enzyme glucose oxidase reacts with the sugar and produces hydrogen peroxide, which, through an electrochemical reaction, extracts current from the doped graphene. This produces an electrical signal proportional to the amount of glucose present. The patch also contains pH and temperature sensors that help ensure that the glucose sensor’s signals accurately reflect the sugar’s concentration in sweat.

When two healthy volunteers wore the patch, the measured glucose levels—including spikes after meals—matched those from a commercial glucose meter. To monitor the levels, the patch sent its sensor signals to a device that analyzed them and then wirelessly relayed the data to a smartphone.

The drug delivery half of the patch consists of an array of 1-mm-tall polymer microneedles that pierce the skin. Each needle is made from a mixture of the diabetes drug metformin and a dissolvable polymer, polyvinyl pyrrolidone. And the needles are coated with a layer of tridecanoic acid. A gold and graphene mesh sits on top of the needle array and serves as a heater that can melt the coatings.

Once the tridecanoic acid melts, the needle dissolves in the skin and releases its drug payload.

When researchers applied just the drug-delivery component to the stomachs of diabetic mice, they could deliver enough metformin to lower the animal’s elevated blood glucose levels by more than 50% in 6 hours.

Guy thinks the sensor portion of the patch is closer to real-world use than the drug-delivery component. To make the drug-delivery system practical, he says, the researchers must make the microneedle array as small as possible. That means they must find a drug that’s effective at low doses.

As for the glucose-detection half of the device, Guy wonders how often a user would have to calibrate the sensors to ensure accurate readings.

Still, he calls the patch an impressive proof of concept.

University of Bath

Researchers gauge quantum properties of nanotubes, essential for next-gen electronics

How do you get to know a material that you cannot see?

That is a question that researchers studying nanomaterials--objects with features at the sub-micrometer scales such as quantum dots, nanoparticles and nanotubes--are seeking to answer.

Though recent discoveries--including a super-resolution microscopy which won the Nobel Prize in 2014--have greatly enhanced scientists' capacity to use light to learn about these small-scale objects, the wavelength of the inspecting radiation is always much larger than the scale of the nano-objects being studied. For example, nanotubes and nanowires-the building blocks of next-generation electronic devices-have diameters that are hundreds of times smaller than the light could resolve. Researchers must find ways to circumvent this physical limitation in order to achieve sub-wavelength spatial resolution and explore the nature of these materials for future computers.

Today, a group of scientists--John A. Rogers, Eric Seabron, Scott MacLaren and Xu Xie from the University of Illinois at Urbana-Champaign; Slava V. Rotkin from Lehigh University; and,William L. Wilson from Harvard University--are reporting on the discovery of an important method for measuring the properties of nanotube materials using a microwave probe. Theirfindings have been published in ACS Nano in an article called: "Scanning Probe Microwave Reflectivity of Aligned Single-Walled Carbon Nanotubes: Imaging of Electronic Structure and Quantum Behavior at the Nanoscale."

The researchers studied single-walled carbon nanotubes. These are 1-dimensional, wire-like nanomaterials that have electronic properties that make them excellent candidates for next generation electronics technologies. In fact, the first prototype of a nanotube computer has already been built by researchers at Stanford University. The IBM T.J. Watson Research Center is currently developing nanotube transistors for commercial use.

For this study, scientists grew a series of parallel nanotube lines, similar to the way nanotubes will be used in computer chips. Each nanotube was about 1 nanometer wide--ten times smaller than expected for use in the next generation of electronics. To explore the material's properties, they then used microwave impedance microscopy (MIM) to image individual nanotubes.

"Although microwave near-field imaging offers an extremely versatile 'nondestructive' tool for characterizing materials, it is not an immediately obvious choice," explained Rotkin, a professor with a dual appointment in Lehigh's Department of Physics and Department of Materials Science and Engineering. "Indeed, the wavelength of the radiation used in the experiment was even longer than what is typically used in optical microscopy-about 12 inches, which is approximately 100,000,000 times larger than the nanotubes we measured."

He added: "The nanotube, in this case, is like a very bright needle in a very large haystack."

The imaging method they developed shows exactly where the nanotubes are on the silicon chip. More importantly, the information delivered by the microwave signal from individual nanotubes revealed which nanotubes were and were not able to conduct electric current. Unexpectedly, they were finally able to measure the nanotube quantum capacitance-a very unique property of an object from the nano-world-under these experimental conditions.

"We began our collaboration seeking to understand the images taken by the microwave microscopy and ended by unveiling the nanotube's quantum behavior, which can now be measured with atomistic resolution," said Rotkin.

As an inspection tool or metrology technique, this approach could have a tremendous impact on future technologies, allowing optimization of processing strategies including scalable enriched nanotube growth, post-growth purification, and fabrication of better device contacts. One can now distinguish, in one simple step, between semiconductor nanotubes that are useful for electronics and metallic ones that can cause a computer to failure. Moreover this set of imaging modes sheds light on the quantum properties of these 1D structures.

Lehigh University