Maynooth scientists build brain sensor

Scientists at NUI Maynooth are building a minute sensor that will measure chemical changes as they take place in the brain. This real-time view of brain function could help us understand illnesses such as epilepsy, explained Dr John Lowry of the university's Department of Chemistry.

Dr Lowry and colleagues are developing a "micro-electro-chemical bio-sensor" designed to be implanted in the brain.

Once in place it can provide information about the chemical processes which allow nerves and brain tissue to fulfil their role as the communications centre of the body. In particular, it responds to a specific neurotransmitter, the specialised chemicals released as nerve cells communicate.

A key to their work is a rare enzyme donated by its manufacturer, Yamasa Corporation of Japan. The company donated 100 5 ml units of the pure enzyme, Lglutamate oxidase, which reacts with the principal neurotransmitter, L-glutamate.

Yamasa Corporation discovered, isolated and then purified glutamate oxidase and was aware of Dr Lowry's work in the development of bio-sensors based on enzymes.

"It is significant because it is a very rare enzyme," he said. Yamasa is the only manufacturer.

Dr Lowry did his PhD at UCD and then went to Oxford where he was part of a group that developed a bio-sensor based on another enzyme, glucose oxidase, which reacts with glucose. The sensor monitored glucose levels in the brain in real time as they fluctuated in relation to different stimuli. "It created a huge stir in the neuro-sciences field," he said.

Bio-sensors have been developed for several things including glucose, oxygen and ascorbic acid, which helps to support many enzyme reactions. "We can now focus on glutamate which is a key neurotransmitter."

The sensors are a combination of platinum, a special polymer and a specific enzyme. The tip of a very fine platinum wire is coated with a polymer that both holds on to the enzyme but also helps suppress other chemical reactions that would interfere with the reactions the bio-sensor was measuring, Dr Lowry said.

This assembly can then be implanted in the brain and is linked to a computer. When the enzyme reacts with the target, such as glutamate, it gives off hydrogen peroxide, and this can be measured by a low voltage applied to the wire. The computer can monitor second-by-second changes in the levels of the target substance, Dr Lowry said, giving the researchers a view into these dynamic chemical processes which are central to the way our brains work.

Very accurate data on glutamate production were not possible before the glutamate oxidase enzyme, he explained, because no other bio-sensor chemical could be as specific to the target. "The beauty of the enzyme is that, once the substrate reacts with the enzyme, it recycles itself. It is a biological catalyst." Sensors had been used for up to six weeks without replacement.

A better understanding of glutamate as a neurotransmitter would provide valuable information about how the brain worked, he said, but might also provide an insight into other roles played by this substance. "There is more and more evidence that glutamate has a metabolic role."

Dr Lowry is building two research groups, one looking at biomedical sensors and one carrying out neuro-chemical research. There will be direct interaction between those developing the sensor devices and those applying them, which should speed up the research process, he said. "We will develop bio-sensors in the first unit and then utilise them in the second."