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Direct spotting of microarrays

Researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) have developed a method that enables the direct spotting of samples from common microtitre plates without further processing. It also avoids the use of different vials and hence minimises sample contamination and false results.

"Stand-alone" i-doT device (Photo: Fraunhofer IPA)
Biotechnology is heading towards processing technologies that involve continuously decreasing amounts of liquid. There are many reasons for this: The substances to be investigated can be very expensive, since many production steps are required; they might also bear biological risks, which will decrease with the smaller amounts of liquids used.

Specific methods and supplies have become standard in scientific investigations. Disposables that are made from injection-moulded polypropylene or polystyrene are frequently used in order to make the expensive process of cleaning and disinfecting sample containers unnecessary. Such microtitre plates (MTP) are available in different forms and sizes.

The development of the new method (I-doT - immediate drop-on-demand technology) mainly focused on improving the possibility of placing the reagents contained in the MTP wells onto microarrays, which is a process that is rather time-consuming and inaccurate when performed with pipettes or manually. Cross-contaminations can only be prevented by exchanging the pipette tips after use.

The new technology is cheap

The researchers had the goal of developing a method that enabled them to remove as small as possible volumes from standard MTPs and to prevent the cross-contamination of the samples. This meant that the dose volumes had to be removed separately from each individual well.

The new technology directly transfers the medium from MTP wells onto a glass slide by way of a very short compressed air impulse. The well bottoms of the slightly modified multiwell plates have fine boreholes to make the capillary pressure in the borehole higher than the pressure exerted by the fluid level in the well. This prevents unintentional leakage. The pressure impulse enables the withdrawal of specific dose units from the well, the volume of which can be controlled by the number of droplets and the length of the impulse.

This method enables the direct printing of samples from multiwell plates and is, therefore, very cheap. The production costs for this type of multiwell plate amount to a few cents, provided that suitable injection moulding tools are used and high enough quantities are produced.

The technology thus allows for the use of disposable multiwell plates. No cleaning steps are necessary after printing. The researchers can simply use a new multiwell plate. Cross-contaminations do not occur because the stamp does not come into contact with the fluid in the well. More sophisticated applications foresee the use of a different stamp for each well since these stamps can also be produced cheaply. The microtitre plate can also be covered with a membrane that is permeable to air, which only transfers the pressure impulse. There are no dead volumes because the multiwell plate can be emptied completely. No expensive and valuable reagents become lost.
i-doT integrated into m:Pal (Photo: Fraunhofer IPA)
i-doT integrated into m:Pal (Photo: Fraunhofer IPA)

Compatible with nearly all the established filling and processing systems

This method is extremely quick; the printing process depends on the volume to be printed and usually takes only a few milliseconds. The traversing units are very quick.

The reactions to be investigated (for example cell growth, purification, etc.) can take place directly in the multiwell plate from which the droplets are subsequently withdrawn. The processing and transfer of the samples into a new vial become redundant and thereby reduce the risk of contaminating the samples. The use of standard multiwell plates makes the system compatible with nearly all the established filling and processing systems.

All kinds of combinations and patterns can be printed onto the slide. It is not necessary to choose a fixed array pattern; mixtures of different patterns are also possible. It is also possible to use a second multi-well plate of any format as a sample carrier, into which variable volumes of the mixtures can be transferred. These can then be spotted onto a suitable carrier with the same system for analysis.

Website address: https://www.biooekonomie-bw.de/en/articles/pm/direct-spotting-of-microarrays