Non-contact dispensing

Various microarrayers deposit the probes in an ordered grid with columns and rows. Two methods are contact printing and non-contact dispensing. 

Piracci AF. Advantages of non-contact dispensing in SMT assembly processes. Chicago, IL Surface Mount Technology Assoc./ATE Sep. 2000. 

In contrast to high density arrays low density arrays are made by deposition of pre-synthesized oligonucleotides or proteins on activated surfaces. There are several printing techniques for fabricating microarrays Non-contact biochip arrayers, commonly based on the piezoelectric effect, can apply controlled sub-nanoliter probe volumes to pre-specified locations on the chip surface. Due to the fact that the dispenser does not touch the surface, a non-contact arrayer provides low risk of contamination and is most suitable for printing on soft materials such as hydrogels. 

Fig. 3 Spotting tools for non-contact printing a Bubble ink-jet A heating coil locally heats the loaded sample, resulting in a changed viscosity and expansion of fluids. The generated droplet can be easily expelled from delivery nozzles, b Microsolenoid A microsolenoid valve, fitted with the ink-jet nozzle is actuated by an electric pulse transiently opening the channel and dispenses a defined volume of the pressurized sample, c Piezo ink-jet A piezoelectric transducer that is fitted around a flexible capillary confers the piezoelectric effect based on deformation of a ceramic crystal by an electric pulse. An electric pulse to the transducer generates a transient pressure wave inside the capillary, resulting in expulsion of a small volume of sample...

The immobilized spots used in protein microarrays may contain protein molecules or smaller molecules such as inhibitors or ligands with which a protein in solution may interact. Very small spots are advantageous in that higher detection throughput can be achieved with minimal amounts of printed material and sample. Spots are typically deposited either by contact methods, such as printing arrayers that use needles to deposit droplets directly on the surface, or by non-contact methods, including the use of capillaries or ink jet dispensers to deposit droplets with nanoliter-picoliter volumes. 

Inkjet and other non-contact droplet formation technologies are able to dispense nanoliter-sized drops onto surfaces, but they offer no control once the liquid has left the confinement of the ejection nozzle and, consequently, suffer from problematic drying and spreading of the ink on... 

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