Figure 3.

Principles underlying enymatic, amperometric microelectrode biosensors. (a) A microelectrode biosensor will generally have a rigid insulating body with a pin at one end for connection to the potentiostat and the fine sensing tip at the other. A Pt wire connected to the pin emerges from the tip of the body to give a defined sensing area. The sensing area is then coated with a special layer, which at the very minimum comprises the enzymatic layer. In some designs, there can be inner and outer selectively permeable layers to exclude electroactive interferences and reduce fouling of the sensor. (b) Examples of two enzymatic cascades used to measure signaling by glutamate and acetylcholine in the brain. Note that the analyte is converted into an electrochemically active product – in this case H₂O₂ – that can be detected by the microelectrode. (c) The analyte of interest diffuses into the enzymatic layer and is catalyzed by the enzymes to peroxide; this then diffuses to the electrode surface through any inner selectively permeable layers. However, interferences can be rejected either by an outer layer, such as cellulose acetate, or by an inner layer, such as Nafion. Adapted from reference¹⁷⁶ with permission. Copyright 2005, Elsevier.