The selection of the appropriate assay plate type is important and mainly depends on the assay
detection method. The light reflecting properties of the assay plate surfaces profoundly affect the
final signal intensities, background noise levels and well-to-well crosstalk. Black, solid bottom,
opaque-walled plates are recommended for fluorescence-based reading technologies to achieve lower
background signal and minimal crosstalk, while white plates are good for luminescence signal
detection to enhance light output. On the other hand, clear-bottom plates are needed for
colorimetric assays, as well as for cell-based assays, where the cells need to be monitored by
microscopy throughout the course of the experiment.
Despite these general selection guidelines, a suitable assay plate type should be carefully chosen
in compliant with the overall project goals. For instance, in a luminescence assay with low signal
window and relatively high assay volume/well, where the "hit" compound is defined as the test sample
that causes a drop in the signal intensity in comparison to the negative control, detection of the
"hits" may be impaired if white plates are used. That is because a well containing the active
compound with low signal intensity would be surrounded by several inactive wells with high signal
intensities, and the crosstalk from the surrounding wells would greatly alter the original signal
magnitude in the active well leading to increased false negative rates. In such luminescence assays,
where the scientist is aiming to detect a signal decrease, black plates would be more appropriate to
conduct the experiment.
High content assays commonly require specially designed microtiter plates to attain the maximal scan
performances, when high content imagers are used. These plates are generally intended to have
optically clear, very thin and uniform well bottoms to ensure high quality images. Additionally, the
assays that require fixation and staining processes, and involve multiple washing steps may
necessitate plates that enhance cell retention. For this purpose, plates with poly-D-lysine,
poly-L-lysine and collagen-coated surfaces are available to promote cell adhesion and growth.
Many more types of plates are offered for different assay methodologies, such as low attachment
plates for cell-based assays using cells in suspension, and non-specific binding surface plates for
protein-binding experiments. Besides, selection of the correct plate type for multiplex assays may
require extra effort and testing process, especially if luminescence and fluorescence signals are
being measured within the same plate. Performing a detailed search of the available plate options
for the assay of interest is a time worthy practice, which would eventually save the scientist from
developing and validating the assay repeatedly.