Understanding Plate Readers and Microplates Quality Control

            Microplate readers are found in most laboratories. They are incorporated as chemistry or immunology instruments in medical facilities or operate as a standalone device used for assay interpretation in university or research facilities.

            Absorption type plate reader performance can be evaluated in an “in-house” QC program. This evaluation is done on the basis of absorption at a specific wavelength, repeatability, and linearity.

            Absorption dyes are an acceptable standard and most useful for plate reader QC at the user's laboratory level. It is best to determine dye absorption values by using prepackaged dyes of known concentrations. Packaged dyes reconstituted at site are a reasonable alternative. These dyes are dispensed into microplates. Once reconstituted a dye plate or strip is useable for several months in multiple testing of a plate reader or several plate readers of different manufacture. Packaged dyes are thereby a very cost-effective control.

             Using pre-dispensed dyes reduces the degree of pipetting precision required to reconstitute these dye strips. Since plate readers read through the samples from top to bottom, volume is proportional to pathlength, and hence, to absorption. If a well is reconstituted with too much water, the decrease in concentration will be corrected by the increase in pathlength. Within reasonable variation this method is self-correcting.

            Using this method in a flat bottom microplate, with a row of: a blank well, a 1:1 dilution, a 1:2 dilution, a 1:4 dilution and a 1:8 dilution of a standard dye, in acidic diluents and a surfactant you can determine absorption at a specific dilution. Repeated readings will result in repeatability and accurate information. Charting of your dilutions will provide the instrument linearity data. Validation and QC programs can be implemented in a lab, several laboratories, a plate reader or several plate readers.

            Problems related to plate reader performance can be ascertained from performance charting. Examples of this are:

All of the above problems are frequent plate reader issues that often go undetected due to lack of a good, cost-effective QC program in the facility.

            Such a low cost kit to test the reliability of a plate reader is available from Caltech Services. This method is able to fully document absorption, repeatability, and linearity to traceable standards. Pre-designed performance documentation is also included to trace instrument performance to NIST standards.

            For help in establishing a plate reader QC program call Caltech Tech Services.