February 4, 2013
Although the patent for PCR expired back in 2006 and promised to herald in a new wave of low-cost thermal cyclers, the legal debate over Taq polymerase enzymes continues to make some manufactures nervous about the North American market. Still, the number of new thermal cyclers to hit the market over the last several years has increased dramatically. As the prices for these work horse devices drops accordingly, the justification for service contracts starts to wane. When opting for a low-cost unit with no local service support, some users may be okay with depot repair or flat-out replacement. When opting for higher quality units, many labs are going with periodic maintenance and routine performance rectification (OQ/PQ). Printed reports or recalibrations by the service tech can be incorporated into your lab’s SOP’s but if you are self maintaining, don’t forget to have the data signed off by more than one person, especially if you are doing forensic or clinical work.
Now, let me put my spin on centrifuge support (wouldn’t be a blog without the occasional pun, now would it?). Seriously, it doesn’t matter whether you have a floor mount, bench top or robot-loaded centrifuge, these devices get a lot of use and it is not uncommon to see units that ten or more years old. Motors and bearings don’t last forever so routine maintenance is critical. Additionally, you folks that leave your rotors in the centrifuge and never take them out should have big scarlet letters painted on your lab coats so you can be publicly ridiculed by the service community! Seriously, many a lab tech has pulled a muscle or two trying to loosen and remove a rotor that has permanently bonded with the spindle.
Last on the docket for this posting is microplate reader upkeep and maintenance. Truly, a wide-ranging topic (may have to post separately on this one to do it justice). The three main readers types (modes) are absorbance, fluorescence and luminescence and while some are limited to one mode, others can do more than one (multimode). Of course there are also fluorescence polarization (FP), time resolved fluorescence (HTRF), high content imagers and microfludic analyzers, but for today we will stick with the big three. All three types work on the basic principle of light measurement to detect samples within the wells of a plate. Absorbance readers use a light source, filters and a detector to measure what percentage of the source light is transmitted through the sample. Fluorescence readers are more sensitive and measure the amount of light emitted from the sample, while Luminescent readers have no light source and instead detect a chemical or biological reaction from the sample. Depending upon the specific reader, any number of factors can result in bad data but generally most failures are a combination of optical alignments (emitter, detector, filters…etc) or light source age. Just about every plate manufacturer provides N.I.S.T. traceable “test plates” that can be used to calibrate the device and a number of third-party companies also have more generic standards that can also be used. It seems patently obvious to say, but what is the point of conducting an assay if you cannot say with a high degree of certainty that your detection results are accurate? At a minimum, plate readers should be PM’d once per calendar year and that procedure should include a test report against a known standard. If your lab only has one reader and it is critical to your research, an annual service contract that includes analytical data would be a wise choice.