A team of scientists at the University of Bath in the U.K. has developed a carbon-based sensor for detecting lactic acid levels in saliva, thereby avoiding the need for an electrical power source.

Working jointly with industrial partner Integrated Graphene, the researchers developed a new type of chemosensor — for lactic acid sensing — that reportedly functions with electricity but without reference electrodes or battery power, thereby offering lower cost, improved shelf-life and ease of miniaturization when measured against enzyme-based sensors.

The Gii-Sens Electrode. Source: Integrated Graphene

The researchers explained that in the lab, the sensor successfully detected lactic acid — which is a by-product produced by the body when it metabolizes carbohydrates or glucose for fuel, for instance, during exercise. According to experts, high levels of lactic acid are associated with the increased risk of becoming unconscious or falling into a coma and major organ failure.

The team explained that their new sensor could potentially be used in remote locations without the need for electricity-powered sensing equipment, unlike current lactic acid measurements, which involve enzyme tests that rely on battery powered sensing equipment.

Instead, the new chemosensor measures lactic acid with a chemical method using a so-called graphene foam electrode surface.

Dubbed "graphene foam" by the researchers, Gii-Sens, which is the technology creating the foundation for the chemosensor, is an electrode manufactured by Integrated Graphene. Gii-Sens incorporates Gii, which is a pure and porous, 3D carbon nanostructure that avoids the use of unsustainable noble metals like gold.

When lactate binds to the sensor, it produces a change in the electrical signal (or quantum capacitance) of the carbon foam. The foam then detects low levels of lactic acid without consuming it by measuring changes in the electrical charging of Gii, thereby enabling the monitoring of changes in levels.

"Just as your contactless credit card doesn't need an external power source to work because the proximity of the card reader is enough to power it — in a similar way, this sensor could create a small, measurable electrical current when lactate binds to it. This sensor, using Gii-Sens technology, addresses some of the main limitations with non-wireless current lactic acid enzyme tests. It will allow for a more simply operated sensor — opening up the potential for more regular, less invasive and more reliable tracking of lactic acid, even during athlete performance," the researchers added.

An article detailing the technology, “Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate,” appears in the journal ACS Sensors.