Successfully miniaturizing assays for high-throughput screening (HTS) often calls for unconventional thinking. Greiner Bio-One is a pioneer in the development of tools for smarter, more efficient high-throughput screening. In particular, our first-in-class microtiter plate designs, materials and high-density formats are trusted throughout the industry for a wide range of biochemical and cell-based applications. In this article, we explore some of the innovative tools and formats that can help you significantly reduce assay volumes and reagent costs, without compromising on assay quality.
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- Jeff Duntemann
Deciding on the best microtiter plate well density – is it time to change your thinking?
The classic “knee-jerk” approach to reducing sample volume is to move to a higher-density assay plate, such as a 384 well or 1536 well plate format. While this may be the obvious choice, that doesn’t necessarily mean it’s the right one.
For a number of reasons, it may be advantageous to stick with a conventional 96 well plate format if that is what is already being used. For instance, workflows to prepare cell-based assays and ELISAs for automated readers often involve manual or semi-automated steps that are relatively easy to carry out in a 96 well plate layout. In many cases, labs shy away from transitioning to higher well densities because these manual steps would become too laborious, and to fully automate them would be too expensive or time-consuming. Additionally, not all laboratory equipment can handle both 96 well and higher-density plate layouts without significant modification.
In these scenarios, Greiner Bio-One’s 96 well Half Area microplates offer an attractive alternative. They are easy to process with multichannel pipettes and standard lab equipment, but at the same time allow a reduction of the sample volume by up to 50%. The reduction in growth area from 32 mm2 to 15 mm2 also provides potential for significant cost savings on applications involving monolayer cell cultures. (Table 1). The range of 96 well Half Area plates includes options suitable for a wide variety of biochemical and cell-based assays involving fluorescence, luminescence or transmission measurements.
Miniaturizing to 384 and 1536 well microtiter plate formats
As we saw in the previous article of this series, moving to higher microtiter plate well densities is a wise choice to get more mileage out of costly reagents and limited samples.
One of the earliest higher format microplates on the market was Greiner Bio-One’ s 384 well microplate, launched in mid 1990s. Compared with a standard 96 well format, the number of wells on the 384 well plate is quadrupled, and the working volume is reduced by about two-thirds.
Being able to fit four times as many wells into the same footprint as a standard 96 well plate was a big step forward for high-throughput screening. However, on a per-well basis, the cost reduction opportunity of a 384 well plate compared to the 96 well Half Area format is modest (Table 1). Transition to a 1536 well microplate is an option, but would require considerable optimization.
Table 1: Comparison of 96 well, 384 well and 1536 well microplate working volumes and growth areas.
To improve the savings potential of 384 well formats, Greiner Bio-One developed the 384 well Small Volume microplate. With a working volume of 4-25 µl and a growth area of 2.7 mm2, the potential reagent savings per well in this format approaches that of 1536 well plates. The 384 well Small Volume microplate is perfect for top and bottom reading, even at low working volumes. These plates are suitable for transmission, fluorescence and luminescence applications, and are available with cell culture and non-binding treatments.
Through close collaboration with Bayer, Greiner Bio-One pioneered the 1536 well microplate format in 1997, demonstrating a commitment to innovation. Further cooperation with numerous users has driven the evolution of a broad product range, with continual quality improvements, such as reduction of plate curvature to less than 100 µm.
Figure 1: Cost comparison of assays in microtiter plates with different well formats
Don’t forget about compound storage
Compound management may be the last thing on your mind when miniaturizing high-throughput screening assays, but it can significantly influence cost and technical implementation of various screening strategies.
For example, the use of direct compound transfer (Figure 2) is a growing trend in high-throughput screening labs because it saves on labor and reagent costs, while reducing the risk of compound precipitation.
Figure 2: Direct compound transfer into “assay ready” plates eliminates intermediate dilution steps used in classical compound management schemes.
In this approach, very low volumes of compound are transferred from the source plate directly into the assay plate, without any intermediate dilution steps. When using this strategy with classical F- and V-bottom well designs, however, it can be difficult to precisely position pin tools or pipette tips for reliable compound retrieval. As a result, valuable sample material is wasted, and there is the risk of incorrect dosing.
To overcome this limitation, Greiner Bio-One developed a completely new well geometry that helps maximize compound retrieval. The 384 Deep Well Small Volume microplate, developed in collaboration with the Compound Management and high-throughput screening groups of Boehringer Ingelheim (Biberach, Germany), is designed to allow perfected positioning of pin tools or pipette tips (Figure 3). This means labs can implement direct transfer protocols without the need for expensive acoustic liquid handling systems. With a working volume of 1-90 µl, these plates are suitable for both direct compound transfer and conventional pre-dilution methods, which are often necessary for cell-based applications. For full details about how this novel design was developed and optimized to support assay miniaturization, read our technical note.
Figure 3: Well geometry of a standard V-bottom microtiter plate (left) and of the 384 Deep Well Small Volume microtiter plate (right).
For direct transfer of volumes in the low nanoliter to picoliter range, acoustic handling systems are often preferred. In this case, Greiner Bio-One's cycloolefin storage plates are popular options. Cycloolefin polymer (COP) and copolymer (COC) materials demonstrate excellent acoustic liquid handling properties. With low water absorption, exceptional chemical resistance to polar solvents like DMSO, and high transparency, cycloolefin plates are ideally suited for compound management and optical density measurements in drug discovery.
To reduce dead volume in liquid handling systems, the wells of the 1536 well COC storage plate are more tapered than classic 1536 microwells (Figure 4). With a working volume of 1-10 µl, this plate is ideal for working with minimal sample volumes, and is also suitable for use with pin tool liquid handling systems.
Figure 4: Well geometry of the 1536 Well COC Storage Plate
There’s so much more
The tools and compound storage solutions featured here only scratch the surface of what Greiner Bio-One has to offer for high-throughput screening and assay miniaturization. You can explore the wealth of available options in our extensive catalog.
With a comprehensive range of microplates designed to meet the demanding requirements of diverse applications in high-throughput screening, we have your needs covered. Still wondering which solutions are best for your application? Let one of our experts show you the way.