Waste coffee grounds may help detect minute levels of neurotransmitters

Nothing beats a steaming cup of coffee to jumpstart your morning. There is now an additional reason to adore the beverage. The first time used coffee grounds have been used as an environmentally friendly electrode coating for sensitive neurochemistry measurements was reported today by researchers. The material may eventually aid scientists in gaining a better understanding of brain activity and in detecting minute concentrations of neurotransmitters.

The researchers will present their findings at the American Chemical Society’s spring meeting (ACS). ACS Spring 2022 is a hybrid meeting that will take place March 20-24 both virtually and in person, with on-demand access available March 21-April 8. The meeting will feature over 12,000 presentations on a wide variety of scientific subjects.

Previously, spent coffee grounds were used to create porous carbon supercapacitors for energy storage. However, new research led by Ashley Ross, Ph.D., has taken recycled coffee waste in a more biological direction. She and her colleagues have demonstrated in vitro that electrodes coated with carbon derived from this waste are capable of detecting trace levels of biomolecules. This is the first time, according to Ross, that residual coffee grounds have been repurposed for biosensing applications.

I read articles about using spent grounds to create porous carbon for energy storage and wondered if this conductive material could be used in our neurochemistry detection work. Additionally, I figured this would be a good excuse to purchase a large quantity of coffee for the lab!”

Principal investigator: Ashley Ross, Ph.D.

Ross is a student at the University of Cincinnati, and several members of her team self-identify as coffee enthusiasts.

Neuroscientists’ traditional microelectrodes are frequently made of carbon fibre -; fine, solid carbon strands bundled together. They are typically made through a lengthy and costly process involving multiple steps and harsh chemicals. Ross eventually hopes to fabricate entire electrodes from carbon derived from coffee grounds, as this method would be both inexpensive and environmentally friendly. To begin, the researchers adapted the material from the grounds to serve as a coating for conventional electrodes.

Kamya Lapsley, a former summer research assistant in Ross’s lab and current undergraduate student at Kent State University, took on this initial challenge. She and other lab members dried used coffee grounds and heated them to approximately 1,300 degrees Fahrenheit in a tube furnace. The material was then activated with a potassium hydroxide solution to create holes in the structure. The mixture was then heated again in the presence of nitrogen gas to remove any undesirable byproducts. What remained was an inky slurry flecked with porous carbon flecks. Finally, the researchers diluted the sludge with water and dipped the carbon fibre electrodes into it to coat them with a porous carbon layer nearly a hundred times thinner than the diameter of a human hair.

The researchers used fast-scan cyclic voltammetry to compare the performance of coated and uncoated electrodes in sensing small amounts of dopamine, a neurotransmitter. They used this technique to alternately oxidise and reduce dopamine by applying a rapidly varying voltage to the electrode. The technique is fast enough to detect neurotransmitter release in the subsecond range, as occurs in the brain. The researchers discovered that electrodes coated with porous carbon generated more than three times the amount of oxidative current as bare carbon fibres when dopamine was present, indicating that the coated electrode provided a more sensitive surface for dopamine detection. Not only does the porous structure allow for greater participation of dopamine molecules in the reaction due to the coating’s large surface area, but it also temporarily traps dopamine molecules in the electrode’s crevices, according to Ross. These properties increase sensitivity and enable researchers to conduct measurements more quickly. The group is now investigating how these porous coatings affect the technique’s temporal resolution.

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