Laser Scribing Builds Molecular Biosensor

Graphene electrodes that act as effective biosensors have been created using a laser to burn patterns into a polymer sheet.

This chemical sensor contains graphene-based electrodes that were inscribed into the underlying polymer using a laser. Courtesy of KAUST/H. Alshareef.

King Abdullah University of Science & Technology (KAUST) researchers used a technique called laser scribing which locally heats parts of a flexible polyimide polymer to 2500 °C or more to form carbonized patterns of patches on the surface that act as electrodes.

These black patches are about 33-μm thick, and their highly porous nature allows molecules to permeate the material.

Lead researcher Pranati Nayak said the graphene sheets inside the patches have exposed edges that are very effective at exchanging 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 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, this electrode could exchange electrons hundreds of times faster than other carbon-based electrodes and showed no loss in performance over 20 cycles of testing.

The team used this graphene-based electrode to build a sensor for three biologically important molecules: ascorbic acid, dopamine and uric acid. Upon hitting the electrode surface, the molecules released electrons, generating a current proportional to their concentration. Crucially, each molecule’s electrochemical response was seen at a different voltage, meaning the device could measure their concentrations simultaneously and without interference.

The electrode accurately detected very small (micromolar) concentrations of the molecules, beating several rival electrodes on both sensitivity and the lower limits of detection.

The researchers now hope to add traces of other atoms, such as nitrogen, to graphene to improve its sensing performance and to augment the electrodes with aptamers — short strands of DNA, RNA, or peptides that bind to specific target molecules — to create new biosensors.