Graphene's Prospects in Biosensing Just Got a Boost

Production technique improves graphene's selectivity in biosensing

2 min read
Graphene's Prospects in Biosensing Just Got a Boost
Illustration: Marc Gluba/HZB

In research that may pave the way for graphene to be used as an effective biosensor, scientists at Helmholtz-Zentrum Berlin for Material and Energy in Germany have developed a way to both measure and control the thickness of an organic compound bound to a graphene layer.

Graphene has presented an attractive option for developing biosensors because of its large surface-to-volume ratio and also because its electrical conductivity quickly decreases as soon as molecules begin to bind to it. 

While this change in electrical conductivity should be a strength in biosensors, the problem has been that graphene’s conductivity changes like this for just about any molecule it comes in contact with, so it lacks the ability to differentiate between molecules—poor “selectivity” as it’s called in the biosensor business.

The German researchers have found a way to improve graphene’s selectivity. To achieve this, the team electrochemically treated the graphene with an organic solution that grafted itself to the surface of the graphene. The organic molecules of the solution essentially served as mounting brackets to which the selective detector molecules could attach themselves.

“Thanks to these molecules, the graphene can now be employed for detecting various substances similar to how a key fits a lock,” explained Marc Gluba, one of the researchers, in a press release.

The bracket molecules on the surface of the graphene are highly selective and will only absorb the molecules that are being targeted.

While other research teams have done something similar to this work, those previous approaches always depended on flakes of graphene that were so small that they resulted in edge effects that have a strong influence on the electronic and magnetic properties of the material and can overwhelm the device, reducing its effectiveness.

Instead of depending on flakes only a few microns in diameters, the German researchers were able to make graphene several square centimeters in size, significantly reducing the deleterious edge effects in the material.

Another key development was a first: The ability to accurately detect how many molecules were actually grafted to the surface of the graphene. The researchers were able to move the graphene layers over to a quartz crystal microbalance such that any increase in mass would change the oscillatory frequency of the quartz crystal. Even a small amount, down to the individual molecular layers, could be measured.

The same amount of precision in measurement could also be achieved in the production by adjusting an applied voltage, making it possible to control precisely how many molecules would bind to the graphene.

The researchers believe that this research should open the way for using graphene in lab-on-a-chip devices that could provide medical diagnosis from a single drop of blood.

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This Implant Turns Brain Waves Into Words

A brain-computer interface deciphers commands intended for the vocal tract

10 min read
A man using an interface, looking at a screen with words on it.

A paralyzed man who hasn’t spoken in 15 years uses a brain-computer interface that decodes his intended speech, one word at a time.

University of California, San Francisco

A computer screen shows the question “Would you like some water?” Underneath, three dots blink, followed by words that appear, one at a time: “No I am not thirsty.”

It was brain activity that made those words materialize—the brain of a man who has not spoken for more than 15 years, ever since a stroke damaged the connection between his brain and the rest of his body, leaving him mostly paralyzed. He has used many other technologies to communicate; most recently, he used a pointer attached to his baseball cap to tap out words on a touchscreen, a method that was effective but slow. He volunteered for my research group’s clinical trial at the University of California, San Francisco in hopes of pioneering a faster method. So far, he has used the brain-to-text system only during research sessions, but he wants to help develop the technology into something that people like himself could use in their everyday lives.

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