Certain molecules can trigger an electrical response when they interact with graphene, making it potentially useful as an electrochemical sensor. One way to enhance its sensitivity is to create a large, accessible surface area of graphene by coating it inside 3D porous materials.
However, this usually requires expensive manufacturing techniques or involves chemical binders that interfere with sensing. Graphene sheets often aggregate, reducing their overall surface area.
To solve these issues, the researchers used a technique called laser scribing. This technique locally heats parts of a flexible polyimide polymer to 2500°C or more to form carbonised patterns of patches on the surface that act as electrodes.
These black patches are 33µm thick and their porous nature allows molecules to permeate the material. Inside the patches, the graphene sheets have exposed edges that exchange electrons with other molecules.
“Graphene-based electrodes with more edge-plane sites are effectively better than those relying on carbon or carbon-oxygen sites in the plane of the material,” said postdoc Pranati Nayak.
The researchers added platinum nanoparticle catalysts to one of the electrodes to speed up the electrochemical reactions with other molecules. In experiments with two different test molecules, the team claims the electrode could exchange electrons hundreds of times faster than other carbon-based electrodes and showed no loss in performance after 20 testing cycles.
The team used the electrode to build a sensor for three molecules: ascorbic acid, dopamine and uric acid. When the molecules hit the electrode surface, they release electrons, generating a current proportional to their concentration.
Each molecule’s electrochemical response was seen at a different voltage, meaning the device could measure micromolar concentrations simultaneously and without interference.