Microbiosensors based on semiconductor fabrication technology are of the order of millimetres in size, but significantly smaller electrodes are required for insertion into the brain or nerve tissue. Now researchers in Japan have constructed an integrated ultra micro enzyme sensor with a 7 μm diameter platinised carbon fibre disc electrode and a platinum thin film counter electrode (E. Tamiya, Y. Sugiura, T. Takeuchi, M. Suzuki, I. Karube and A. Akiyama, Sens. Actuators B, 1993, 10, (3), 179–184).

The surface of the carbon fibre electrode was platinised electrochemically, which increased the electrode activity sufficient for the sensor to be used for the determination of glutamate, an important neurotransmitter.