Parameters Affecting the Variability of Cell Based Assays.

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The following abstract was presented as a poster at the May 1998 Annual Meeting of the American Society for Microbiology in Atlanta, GA.  This presentation focused on the variation associated with animal cell -based assays, but it applies to tissue culture in general.  Since this time, a new device has been designed which focuses on creating a uniform environment for tissue culture.  Animal cells grown in the device have much less variation. If you have any questions, please feel free to contact us at



In vitro cell based assays employing animal cells are extremely sensitive to variations in extrinsic chemical and physical parameters. In order to develop an incubator specifically designed to minimize these variations, we have investigated the effect of temperature, osmolality and pH variations, as controlled by several commercially available carbon dioxide incubators, on cell based assays. Temperature is directly controlled by heating elements while osmolality and pH are indirectly affected by incubator humidity levels (impacting evaporation) and carbon dioxide concentration. Though thermal mapping of incubators suggests a homogeneous chamber temperature, analysis of customized 96 well microtiter plates designed with multiple temperature probes reveal inconsistencies between microtiter plates. This temperature variability could lead to differential cell growth rates. However, a comparison of the pH of microtiter plate wells incubated at room temperature and in an incubator demonstrate that an incubator can lower the pH variation between wells (data not shown). Unfortunately, this effect is not uniform but dependent upon the position of the assay plate within the incubator. It is unknown whether the variability in pH is a result of the microtiter plate, fluctuations in carbon dioxide concentrations, and/or influenced by carbon dioxide solubility as related to temperature variations. Evaporation from plates was examined by measuring changes in conductivity of culture medium. Evaporation occurred unevenly across the microtiter plate and its position within the incubator chamber, with a low of 0% for an interior well to a high of 59% for an outer well. High levels of evaporation occurred despite conventional efforts at humidifying the chamber. To correlate a cell based assay to measured parameters, cell growth rates were used to provide a comparison. Following a two day incubation period, cell growth variations in culture dishes confirms cells are influenced by their location within the incubator. Reducing the effect of these variations on cell based assays is possible by reconfiguring current incubators so to create greater environmental homogeneity.
Related Products:  Microplate Stability Chamber

Tissue culture and animal cell based assays often have high variation
Cultured cells are dramatically affected by the environment created by the incubator.  Animal cell based assays can have CVs of 50% if environmental parameters are not controlled to reduce variation.

See Microplate Stability Chamber