Printing of microarrays into micro well plates
Authored by: Biofluidix GMBH
Reprinted with permission by Biofluidix GMBH
An unique feature of the PipeJetTM technology is the dispensing pipe, acting as nozzle and providing an adjustable free length combined with a very small outer diameter. This enables its use for applications, which need a highly precise sample positioning also for non-planar substrates. One of these applications is the printing of microarrays into micro well plates.
A microarray consists of a multitude of small sample spots, arranged in a regular order. To enable a defined reaction of all samples in one array with one common reagent, micro well plates are particularly suitable because they offer a well-known and essential reaction platform in the field of life sciences. The challenge is the accurate positioning of all spots of the array into the up to 11 mm deep wells of standard SBS micro well plate. Many currently available low volume dispensers would have to eject the sample from top of the well because they have too large dimensions for immersing the nozzles into the wells. This results in very irregular array patterns because the droplets are strongly deflected during their flight from the top to bottom of the well. Other available dispensers do allow the immersion into the wells but they provide too large diameters of the nozzles what prevents printing of arrays with many features.
The currently recommended and available PipeJetTM configuration for applications with non-planar substrates is a free pipe length of 13 mm and an outer pipe diameter of only 600 μm (see top picture). The maximum feature density of the microarray depends on dispense volume as well as on sample and surface properties. Typical material properties and a dispense volume in the range of 10-20nl allow up to 6x6 microarrays in the 11 mm deep wells of standard flat bottomed 96 micro well plates.
The bottom picture in the figure shows results of a microarray spotting run. Arrays with a 3x3 pattern were printed into all wells of a 96 well plate. Overall only about 10% of the wells showed a slightly distorted array due to mostly only one or two misaligned spots. Rarely one of the wells showed at least one completely missing spot or a spot positioned at the well wall.
The main issue responsible for misalignment of droplets are the strong electrostatic charges of the micro well plates after delivery. Though the PipeJetTM system allows the sample deposition with distances below 1mm between nozzle and bottom of the well, arrays might show an irregular pattern if the electrostatic charge was not reduced before microarray deposition. Insufficient charge minimization is also expected to be the reason for the found misaligned arrays in the shown experiment. Therefore proper discharging and grounding of well plates is essential for spotting into micro well plates!
The presented experiment was conducted with a single channel BioSpot® workstation. Due to the movement time needed for positioning the dispenser from well to well and the times needed for cleaning and reloading the dispenser with the next sample it takes at least one hour to process one 96 micro well plate with a 4x4 array. Because the BioSpot® workstation supports the parallel use of up to eight PipeJetTM dispensers, the handling time can be reduced to some tens of minutes if all eight PipeJetTM dispensers are operated in parallel.
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