Each piezoelectric head can deliver picoliter volumes of reagents or solutions.
The diameter of each capillary is only 55um.
The volume of each droplet is less than 100pL.
4 piezoelectric heads can deliver 4 different solutions to specific locations on a target surface. This can also ensure that incompatible reagents for different applications will not come into contact.
For example, proteins bound to a PVDF membrane after blotting are probed with primary then secondary antibodies by western blotting.