A microplate, often referred to as a microtiter plate, is a standardized, flat tray containing an array of small cavities called wells, which act as miniature test tubes. This equipment has become fundamental to modern biological and chemical laboratories since its invention in 1951. The plate’s design allows scientists to manage a high volume of samples in a small space, streamlining processes that were once performed in individual glassware. Its introduction enabled the parallel processing of experiments, significantly increasing the speed and efficiency of research.
Physical Structure and Standardization
Microplates are typically manufactured from robust plastics like polystyrene or polypropylene, with the material choice depending on the specific experiment. Polystyrene is selected for assays requiring optical clarity, such as measuring light absorption. Polypropylene offers superior chemical resistance and temperature stability for applications involving organic solvents or temperature cycling. The plates adhere to a strict standardized footprint set by organizations like the American National Standards Institute (ANSI) and the Society for Laboratory Automation and Screening (SLAS). This common outer dimension ensures seamless integration into automated laboratory equipment.
The internal structure is defined by the number of wells, which commonly come in formats of 96, 384, or 1536, arranged in a precise rectangular grid. The volume of liquid each well can hold decreases as the number of wells increases, ranging from milliliters in low-density plates to nanoliters in ultra-high-density formats.
The shape of the well bottom is customized for different experimental needs. A flat-bottom (F-bottom) is preferred for optical measurements and for growing adherent cells, as it maximizes light transmission. A V-bottom (conical) well maximizes the recovery of small liquid volumes and is useful for precipitation-based assays or sample storage. A U-bottom (round) facilitates efficient mixing and washing of samples, often used in immunological tests.
Operational Purpose: Miniaturization and High-Throughput Screening
The microplate’s primary functional advantage is the dramatic miniaturization of assays, allowing scientists to conduct experiments using small volumes of costly reagents and precious samples. By reducing the necessary volume per test point, the microplate significantly cuts down on overall research costs and conserves rare biological materials. This reduction in volume also facilitates parallelism, meaning multiple tests can be performed simultaneously on a single plate.
This combination of small-volume testing and parallel processing is the foundation of High-Throughput Screening (HTS), a methodology central to modern drug discovery. HTS allows researchers to rapidly screen massive libraries of chemical compounds against a biological target, such as a disease-related protein. Automated systems process thousands of data points per day using microplates, drastically accelerating the pace of scientific investigation.
Common Scientific Applications
Microplates are utilized across a broad spectrum of life science and health applications. One of the most widespread uses is in immunoassays, particularly the Enzyme-Linked Immunosorbent Assay (ELISA). ELISA is a technique used to detect and quantify substances like antibodies, proteins, and hormones in a sample, often used in clinical diagnostics. The microplate’s surface is specially treated to allow the binding of biomolecules, making it ideal for the sequential steps of an immunoassay.
Microplates are also extensively used in cell culture, where small batches of cells are grown and maintained in the wells for experimental testing. This allows researchers to study the effects of various drugs or environmental conditions on cells in a controlled environment. In genomics, microplates are used to prepare and process samples for techniques like Polymerase Chain Reaction (PCR). Using microplates, the preparation of hundreds of DNA samples for sequencing or genetic analysis can be automated efficiently.
Associated Instrumentation
The power of the microplate is fully realized when it is integrated with an ecosystem of specialized laboratory instruments. The most important piece of associated equipment is the microplate reader, a sophisticated device that measures the results of the experiments within the wells. These readers utilize different detection modes, such as spectrophotometry (measuring light absorption), fluorometry (measuring light emission), and luminometry (measuring light from chemical reactions). The type of reader used depends entirely on the signal generated by the assay.
To manage the high volume of samples and reagents, liquid handling robots dispense precise, small volumes into the microplate wells. These automated systems eliminate human error and ensure the accuracy required for miniaturized assays. Other instruments, such as plate washers, are necessary for cleaning the wells between steps in multi-step assays like ELISA. This interconnected system enables the fully automated, high-speed execution of scientific experiments.