Spending an afternoon washing out microplate wells by hand is no one’s idea of fun. Happily, microplate washers exist to do the job for us.
Washers generally are used in assay workflows to dispense and aspirate wash buffer from microplate wells, removing unbound material and leaving samples ready for the next step in the process. They serve a different, though overlapping, function than a liquid-handling robot, which is commonly used in automated environments to add samples to microplate wells, perform dilutions and dispense reagents throughout a workflow, with washing steps interspersed throughout.
Many models of washer are available, and it’s important to focus on your specific requirements to ensure you end up with the most appropriate instrument for your application.
“There are a variety of washers available to meet scientists’ needs, from the most basic strip washer to those that dispense and integrate with automation,“ says Celeste Glazer, product manager at Molecular Devices. ”As the complexity of the application increases, so does the need for a more sophisticated washer.”
Factors to consider
So what factors should you be considering to ensure that you pick the instrument that’s right for you?
First, think about the plates you use in your lab’s assays. Number of wells per plate, well depth (standard or deep) and your throughput requirements may all impact your decision. “If only a few samples are processed at a time, a strip washer may be of interest,” says Jason Greene, senior product marketing manager at BioTek Instruments. (Strip washers work like a multichannel pipette, washing rows in multiples of eight, 12 or 16 in a stepwise fashion across the plate.) A full plate-style washer is more appropriate for busy screening labs, he adds, but keep in mind that machines with higher throughput come with heftier price tags.
Next, think about the kinds of procedures you’ll be doing. More complicated assays may require more wash lines to dispense different solutions. (Washers generally have one to four lines). And if biomagnetic separation or vacuum-filtration processes are required, look for microplate washers that supports those capabilities as well, Greene says.
You’ll also have some options in terms of the number of channel heads—a variable that impacts system speed. ”Systems with a strip head, usually an eight-well strip, will take longer to wash because they must wash the wells row by row,” explains Glazer. ”Systems that have a 96- or 384-well head can wash a 96- or 384-well plate in one round, and for larger plates they can cover more wells faster.” If you opt for a washer with more than one type of head, it’s important to assess the labor required to change manifolds, Glazer adds. Some can be changed by simply moving a lever, but others require tools and calibration.
Not all washers can dispense reagents, but models that can wash and dispense will save you time. Researchers performing ELISAs may want to consider a model that has this function, as ensuring an even plate coating and optimizing subsequent wash conditions are important for success. Using a washer improves consistency and accuracy vs. manual methods using pipettes and shaking off excess solutions, and is also also much faster. Molecular Devices’ MultiWash™+ washer can accurately dispense the coating solution and then be programmed to shake the plate to ensure even coverage.
Another key feature is automation, and in particular, the ease with which your system can be integrated into an automated workflow. ”Depending on the number of plates that you want to run and how quickly you need to read the plates after washing, automation integration is important,” says Glazer. ”Many washers have been integrated from pre-plate processing to post-read processing using robotic integration.“
Finally, consider durability and maintenance, says Kamni Vijay, marketing manager at Bio-Rad Laboratories. ”Microplate washers should last five to 10 years—most of the maintenance is in cleaning and flushing lines and pins,“ he explains. A properly maintained washer could serve you well for up to 20 years, as long as all the internal plumbing is kept clean (which involves flushing the lines every day, avoiding corrosive substances like bleach and annual checks of the instrument’s tubes for cracks). BioTek’s patented Ultrasonic Advantage™ system, which is incorporated into most of that company’s microplate washers, uses ultrasonic vibrations to clear the manifold tubes of protein and salt-crystal buildup.
Pricing
Microplate washers vary from a few thousand dollars to as much as $65,000, depending on the features and automation they offer. “More costly instruments will support a broader range of applications, accommodate a range of plate types, integrate multiple-wash buffer switching and often have abilities to dispense reagents to microplates along with washing for a fully integrated washer/dispenser solution, entirely automating a lab’s conventional ELISAs,” explains Greene.
Lower-end models are generally strip washers that can handle one or two solutions. Mid-range options usually have 96- or 384-well heads plus a dispense function and can accommodate several solutions. BioTek’s ELx50™ strip washer is particularly popular in lower-throughput labs, says Greene; it is often sold by reagent partners together with various specialty kits as a complete solution. The firm’s ELx405™ washers are its most popular automated microplate washers, offering a variety of models within the 405 family. Other options include Molecular Devices’ MultiWash+ and Brooks Life Science Systems’ SQUIRT™.
More costly machines boast similar features to the mid-range models, but they offer greater speed. These instruments tend to be most popular in high-throughput settings like drug-discovery labs. Molecular Devices’ AquaMax® washers, for example, can reportedly wash an entire 96-well plate in 11 seconds and a 384-well plate in 12 seconds. “Imagine doing that manually with a multichannel pipette,“ says Glazer. ”It could take 10 to 15 minutes per plate for ELISA washing, if done by hand.”