In situ mapping of community-level cellular response with catalytic microbiosensors.

Chemotaxis, the migration of cells in the direction of a spatial chemical gradient, is important in disease progression, microbial ecology, and bioremediation. The ability to map chemoattractant gradients and the corresponding cellular growth and motility patterns is essential to the study of chemotaxis. Microelectrodes and microbiosensors have the potential to measure chemoattractant gradients with high spatial resolution. In this study, Clark-type amperometric microelectrodes and microbiosensors were used to measure solute concentrations gradients generated by a chemotactic band of Escherichia coli in a semi-solid gel. A computerized image analysis system was used to simultaneously measure the cellular concentration profile across the chemotactic band. The experimental results compared favorably with a mathematical model of solute and cell transport in the gel. Scanning electron micrographs (SEM) of micro(bio)sensor tips taken after 6 months of use showed evidence of degradation, including adhesion of foreign particles to the glass body, the adhesion of a small gel capsule to the sensor tip, and separation of the bio-interface from the tip. A needle-type microbiosensor was constructed to better protect the tip and hence increase the ruggedness of the microbiosensors.