Power/Performance Bits: Sept. 24

Textiles for energy storage
Scientists at RMIT University developed a way to laser print waterproof textiles with graphene supercapacitors for embedded energy storage. The process takes three minutes to create a 10x10cm patch.

The electronic textile is based on nylon coated with PDMS on one side for waterproofing. The other side was paint coated with graphene oxide and a binder to form thin films 3 µm thick, which was used as the base for the laser-printed graphene supercapacitors. The binder also acted as waterproofing.

The material is flexible, stretchable up to 200%, and machine washable. The team says it would be a less cumbersome alternative to coin-cell or pouch cell lithium-ion batteries and higher storage capacity than fibers incorporating electrode, separator, and electrolyte.

Laser printing also would provide benefits over other printing methods such as inkjet and screen printing by lowering the number of additional steps in manufacturing and overall reducing fabrication times.

The new technology can produce a 10×10 cm smart textile patch in just 3 minutes. (Credit: RMIT University)

“Current approaches to smart textile energy storage, like stitching batteries into garments or using e-fibres, can be cumbersome and heavy, and can also have capacity issues,” said Litty Thekkakara, a researcher in RMIT’s School of Science. “These electronic components can also suffer short-circuits and mechanical failure when they come into contact with sweat or with moisture from the environment.

“Our graphene-based supercapacitor is not only fully washable, it can store the energy needed to power an intelligent garment – and it can be made in minutes at large scale. By solving the energy storage-related challenges of e-textiles, we hope to power the next generation of wearable technology and intelligent clothing.”

In a proof of concept, the fabric supercapacitor was charged by a washable solar cell, with stable performance for 20 days. It also remained stable and efficient in mechanical, temperature and washability tests.

The technology could enable real-time storage of renewable energies for e-textiles, said Min Gu, RMIT Honorary Professor and Distinguished Professor at the University of Shanghai for Science and Technology. “It also opens the possibility for faster roll-to-roll fabrication, with the use of advanced laser printing based on multifocal fabrication and machine learning techniques.” The researchers have applied for a patent on the technology.

Insulating chips
Researchers at KU Leuven and Imec proposed a new technique to insulate microchips using metal-organic frameworks in an effort to support smaller, lower power chips.

“We’re using metal-organic frameworks (MOFs) as the insulating substance. These are materials that consist of metal ions and organic molecules. Together, they form a crystal that is porous yet sturdy,” said Rob Ameloot, a KU Leuven professor.

To apply the MOF insulation to electronic material, the team used chemical vapor deposition.

“First, we place an oxide film on the surface. Then, we let it react with vapour of the organic material. This reaction causes the material to expand, forming the nanoporous crystals,” explained Mikhail Krishtab, a postdoctoral researcher at KU Leuven.

“The main advantage of this method is that it’s bottom-up,” said Krishtab. “We first deposit an oxide film, which then swells up to a very porous MOF material. You can compare it to a soufflé; that puffs up in the oven and becomes very light. The MOF material forms a porous structure that fills all the gaps between the conductors. That’s how we know the insulation is complete and homogeneous. With other, top-down methods, there’s always still the risk of small gaps in the insulation.”

The team received an ERC Proof of Concept grant to continue developing the technique. At Imec, they will be working on scaling up for use in fabs. “We’ve shown that the MOF material has the right properties,” Ameloot said. “Now, we just have to refine the finishing. The surface of the crystals is still irregular at the moment. We have to smoothen this to integrate the material in a chip.”

Norovirus detection
Researchers at the University of Arizona developed a paper microfluidic chip that can be used with a smartphone to detect norovirus in water samples.

Ingesting even small amounts of norovirus is enough to cause illness, making it important to be able to detect even small quantities. It can spread rapidly through a community’s water supply. Each year, it causes about 200,000 deaths globally and about 20 million cases of food poisoning in the U.S.

Typically, detecting small quantities of norovirus requires a laboratory setting with an expensive array of microscopes, lasers and spectrometers, making it infeasible for cases such as cruise ships and rural areas. For this kind of field detection, the team turned to paper microfluidic chips.

“Paper substrate is very cheap and easy to store, and we can fabricate these chips easily,” said Soo Chung, a biosystems engineering doctoral student at University of Arizona. “The fibrous structure of paper also allows liquid to flow spontaneously without using the pumping systems other chips, such as silicon chips, usually require.”

A sensitive new device can detect tiny amounts of norovirus in water. (Credit: University of Arizona)

The process starts with adding potentially contaminated water to one end of a paper microfluidic chip. To the other end, a tester adds tiny, fluorescent polystyrene beads. Each bead is attached to an antibody against norovirus. If norovirus is present, several of the antibodies attach to each virus particle, creating a little clump of fluorescent beads.

“Norovirus particles are too small to be imaged by a smartphone microscope, and so are antibodies,” said Jeong-Yeol Yoon, a researcher in the Department of Biomedical Engineering at UA. “But when you have two or three or more of these beads joined together, that indicates that the norovirus is there, causing the beads to aggregate.”

The clumps of beads are large enough to detect and photograph with a smartphone microscope. The microscope, at around $50, is the most expensive component of the device. An app created by the researchers counts the number of illuminated pixels in the image to identify the number of aggregated beads, and thus the number of norovirus particles in the sample.

“You don’t have to be a scientist or an engineer to run the device,” Yoon said. “Analysis will be done automatically by the smartphone app, so all you have to worry about is loading a sample of water onto the chip.”

The team hopes to create ways to detect norovirus in patients as well as other hazardous viruses or chemicals.