Analysis of chemical dynamics in microenvironments Original Research Article

A variety of techniques exist that provide chemical information in the form of a spatially resolved image. For example, magnetic resonance imaging has significant advantages for biological applications because it allows measurements in intact tissues. However, it is restricted at the present time to species of high concentration. The most common approach for chemically selective imaging is to use optical microscopy coupled with fluorescence measurements. A variety of fluorophores with high selectivity for specific ions are commercially available and are readily used in such applications. While imaging techniques provide an overall view of the microenvironment, probes that give a high fidelity view of a specific species and its concentration at a single location are also useful. Thus, there is particular interest in developing local sampling techniques. Electrochemical techniques, both potentiometric and amperometric, are particularly useful in this regard. For example, neurotransmitters, compounds secreted from nerve terminals to relay information from one neuron to another, can readily be examined with electrodes of micrometer dimensions. In this way, the mechanisms that control the secretion and the regulation of these compounds in the extracellular space can be evaluated. These tools can also be used at the level of single cells, and when placed at different locations, can be used to provide a chemical image. This approach essentially represents a marriage of electrochemical techniques with those of the scanning microscopies, an area that will see considerable growth in the new millennium.