Scientists at the University of Virginia, US, have developed a sensor able to detect both dopamine and serotonin simultaneously in vivo for the first time.

Dopamine and serotonin are important neurotransmitters. Serotonin is known to regulate sleep and is a common target for depression medication. Dopamine has been linked to locomotion, reward and motivation and is a common target for illicit drugs. The death of dopamine receptors is the cause of Parkinson's disease. However, the two are inherently linked; cocaine is known to act on both dopamine and serotonin transporters, for example. Consequently, the simultaneous, rapid, in vivo detection of these compounds is a requirement if their interactions in the brain are to be understood.

Jill Venton and Kumara Swamy at the University of Virginia developed carbon nanotube modified microelectrodes that allowed them to detect serotonin and dopamine with cyclic voltammetry with increased sensitivity and resistance to fouling. Normally, the detection of both compounds simultaneously with electrochemistry is difficult due to their similar oxidation potentials. Detecting dopamine causes fouling by serotonin, while methods to avoid serotonin fouling prevent dopamine detection.

'We showed that carbon nanotube sensors have increased sensitivity for dopamine and serotonin and are more resistant to fouling by oxidative products of serotonin,' explained Venton. This allowed them to monitor both compounds at the same time. They went on to monitor release of both neurotransmitters in the brains of anaesthetised rats.

Mark Wightman, an expert in neurochemistry and electrochemistry at the University of North Carolina, Chapel Hill, US, appreciated the significance of their new technique. 'In vivo voltammetry at carbon-fibre microelectrodes provides the only way to follow the release and uptake of neurotransmitters in the brain as they control rapid behaviours on a second-to-second time scale.' he said. 'This new approach by Venton that employs carbon nanotubes provides a new approach that has several advantages.'

Although it is still unclear how the carbon nanotubes increase resistance to fouling Venton hopes the microelectrodes will allow further studies of dopamine and serotonin in the brain. 'The next challenge,' she said, 'is to create even smaller, nanotube based electrodes to more closely approach the small size of synapses.'

Edward Morgan