Several factors are known to increase the noise and variability of cell-based assays used for high-throughput screening. In particular, edge effects can result in an unacceptably high plate rejection rate in screening runs. In an effort to minimize these variations, the authors analyzed a number of factors that could contribute to edge effects in cell-based assays. They found that pre-incubation of newly seeded plates in ambient conditions (air at room temperature) resulted in even distribution of the cells in each well. In contrast, when newly seeded plates were placed directly in the CO2 incubator, an uneven distribution of cells occurred in wells around the plate periphery, resulting in increased edge effect. Here, the authors show that the simple, inexpensive approach of incubating newly seeded plates at room temperature before placing them in a 37°C CO2 incubator yields a significant reduction in edge effect.
While this article does not speak specifically to chemotaxis assays, it does speak generally to cell-based assays, of which chemotaxis assays are certainly part. We are not necessarily recommending this practice, but offer it for your consideration.
Available online at: http://jbx.sagepub.com/content/8/5/566