Assay Type
The first factor to consider is whether you'll be performing a biochemical assay or a cell-based assay, which narrows down the type of surface needed. Biochemical assays often have fewer surface requirements, while adherent cell culture may have specific requirements for surface treatments, such as tissue culture treated, Corning® CellBIND®, BioCoat®, or Matrigel® Matrix. An ultra-low attachment surface is available for spheroid formation.
Detection Type
The second factor to weigh is the type of detection, which will determine the microplate color. Clear microplates are typically used for absorbance assays. White microplates are recommended for luminescence and time-resolved fluorescence; the white surface reflects and amplifies the potentially weak signal and reduces well-to-well crosstalk. Black microplates are appropriate for most other fluorescence assays because the signal intensity is higher. The black surface also reduces well-to-well crosstalk and background autofluorescence.
Reader Type
The third factor to consider is the type of reader that will be used, which will help determine whether the bottom of the microplate should be solid or clear. When reading from the top of the microplate, a solid black or solid white bottom may be appropriate. When reading from the bottom of the microplate, a clear bottom is essential, which can be paired with solid black or solid white sides. When using a spectrophotometer, an ultraviolet-transparent bottom may be required.
Using microplates for microscopy presents unique challenges, especially for high content screening (HCS) with automated microscopy, image acquisition, and analysis.
"For imaging applications, throughput time for microplate read is impacted by plate flatness," Brown explains. "If it is taking a very long time to scan a microplate due to the need to refocus, select a microplate designed for high content imaging that has more uniform flatness."
Corning offers microplates with a variety of clear bottom substrates for high content screening microscopy. For low magnification 2X-10X microscopy, a clear polystyrene bottom is typically sufficient. For 10X-32X microscopy, a 96-well microplate with a glass or COC bottom is recommended. The scratch-resistant Willow® Glass bottom delivers high optical quality that reduces autofocus time, while a COC bottom offers the clarity of glass without the glass. For microscopy at 40X and higher, Corning offers 96-well, 384-well, and 1536-well microplates with a COC low base. Unlike the standard base, the low base is designed for imaging with high magnification objectives. The exceptional flatness of the COC base allows for unobstructed reading to the edge of the microplate.
Throughput Needs
The fourth factor to consider for microplate selection is the throughput needed. For low throughput screening or assay development, 96-well microplates are often appropriate. Moderate and high throughput might require 384-well or 1536-well microplates, respectively. Within these formats, additional options are available.
"Half area 96-well microplates and low volume 384-well formats are nice for customers that aren't quite ready to move to the next well size, as they maintain the same number of wells but can provide cost savings on reagents," Brown notes. Stripwell™ 96-well plates may also be useful in the development phase, as you can use less than 96 wells at a time.
According to Brown, you should start exploring 384- and 1536-well formats when throughput needs outstrip the feasibility of running the assay in 96-well plates. For example, testing 1 million compounds would require over 10,000 plates with 96 wells but only 2,600 plates with 384 wells and just 650 plates with 1536 wells. Miniaturization can be especially attractive when using expensive reagents.
When choosing between 96-well, 384-well, and 1536-well microplate formats, one important consideration is access to the appropriate equipment for liquid handling and automation.
"Make sure the equipment being used is designed for the microplate type, otherwise you could introduce unwanted variability in the test results" Brown emphasizes. "For example, you shouldn't use a manual multichannel pipette designed for a 96-well microplate for a 1536-well microplate." There is a trade-off between ease of use and throughput, with automation being absolutely essential for 1536-well microplates.
Taking the time to make well-informed choices about plate selection and automation can help reduce variability and improve results, ultimately accelerating the pace of scientific discovery.
