Selective detection of glutamate in brain tissue using microelectrode arrays has been achieved by scientists in the US.

Glutamate is an amino acid neurotransmitter and plays an important role in the mammalian central nervous system. A number of neurological and psychiatric disorders are thought to be linked to abnormalities in the transmission of glutamate.

Nigel Maidment and his colleagues at the University of California, Los Angeles, therefore developed ceramic-based platinum microelectrode arrays (MEAs) coated with an electropolymerized, overoxidized polypyrrole (OPP) that selectively detects glutamate in brain tissue.

The challenge has been for scientists to develop selective glutamate sensors with sensitive and rapid responses to glutamate. They should also not experience interference from other neurotransmitters, such as dopamine (DA) and ascorbic acid (AA). Interference is usually caused by the direct oxidation of DA or AA at the platinum electrodes.

Current methods use electrodes coated with Nafion, a well-known co-polymer, to overcome this problem. Maidment and his team showed that using their OPP-coated MEAs produced similar glutamate sensitivity and response times to those previously found for Nafion-coated MEAs. Unlike the Nafion-coated MEAs, their system is not affected by DA (at a concentration of 5 µM), which results in a highly selective glutamate detection.

Maidment's future plans 'are to selectively load different enzymes onto individual sites on multi-electrode arrays, thereby permitting detection of several neurotransmitters simultaneously'. But the team's primary challenges are 'improving sensitivity, longevity and further miniaturization [for these systems]', said Maidment.

Emma Shiells