Preventing Edge Effect In Microplates
Microplates are essential tools for the assay biologist, whether performing biochemical or cell-based assays. Biochemical and cell-based assays share the issue of edge effect. The primary cause for the “edge effect” phenomenon is evaporation and is commonly associated with 96-well microplates. “Edge effect” is an issue attributed to the increased evaporation rate of circumferential wells compared to the centrally-located wells.
Evaporation results in a change in the concentration of salts and reagents in the assay buffer or media in the circumferential wells compared to the wells located in the center of the microplate. This phenomenon results in an increase in CV values, directly impacting assay robustness or the z-factor. The change in osmolarity or concentration of the reagent can cause assay failure or in cell-based assays a drop in overall cell viability.
- Reduce assay time, when possible, reduce the amount of time fluids are stored in the well, resulting an overall reduction of evaporation.
- Utilize a low evaporation lid to reduce fluid loss, to protect samples from evaporation and contamination consider using a lid with condensation rings. The chimney well design of the 96-well standard plates in combination with the condensation rings substantially reduce the risk of contamination and evaporation.
- Use a clear or foil sealing tape for biochemical assays or a breathable sterile tape for cell based assays. Heat sealing microplates using rolls of film has been an effective method for significantly reducing the impact of edge effect in biochemical assays (most efficient way to prevent microplate “edge effect”). Breathable sterile tape for cell-based assays allows for gas exchange.
Microplate Edge Effect
The “edge effect” is a discrepancy between the center and outer wells (local environment), where each well has it’s own unique environment. This effect is not exclusive to 96-well microplates but is seen in all microplate formats, commonly in 96-, 384-, and 1536-well formats. “Edge effect” caused by evaporation is a very real phenomenon and can greatly impact your assay results. The 384- and 1536-well microplates may experience a more pronounced “edge effect” due to the extremely low volumes of the microplates.
Since microplate “edge effects” are related to the design of the plate it is difficult issue to solve. The three helpful tips above have been used to successfully reduce “edge effect” but there are a couple of other tips to consider. As previously discussed, the outer edges aren’t insulated like the inner wells of the microplates. Although this is not al ideal solution it can work, place a fluid such as water or media and simply disregard the data from these well. By following this method you will sacrifice data points. Transparent bottom microplates have an outer wall along the outer edges which can provide better insulating qualities than traditional solid microplates and as a result may be better suited for assays.
Preventing Microplate “Edge Effect”
To briefly recap, there are three ways to manage and reduce the “edge effect” caused by evaporation.
- Reduce assay time
- Use a low evaporation lid
- Use a sealing or breathable tape
The phenomenon of “Edge effect” is dependent on assays generally associated with a longer runtime and assays with with a runtime of several hours will not be affected the same way. If you have experienced issues with “edge effect” and would like to share your experience please feel free to leave a comment below. When selecting a microplate ensure that you pick the correct color and correct micoplate format since the microplates with transparent bottoms may provide better results compared to the solid 96-well microplates. Please feel free to contact us to request a free consultation to assist you in selecting the appropriate microplate for your assay.