adapted to a multiwell plate in which each well has a relatively large number of posts it is possible in one embodiment for the ligand spots to be smaller than the dimensions of the posts in this embodiment one may print ligand arrays on the side walls of the posts since typical ligand spots are on the order of 100 microns this would be more practical with posts having at least one dimension greater than three times the diameter of a spot or greater than 300 microns in this case for example for 2d arrays on sidewalls posts could be 1 cubic millimeter with each side wall containing 25 ligand spots for 1d arrays the posts can be made 100 microns high 100 microns thick and 1 mm wide to accommodate five spots on the longer side wall minimizing the height of the posts is advantageous for allowing one to use very small sample volumes in another embodiment of the type shown in fig5 and 6 the post dimensions are smaller than the dimensions of microarray spots ligand spots may be introduced to subsets of the posts in a well where they completely cover multiple posts e g see spots 37 in fig2 and 5 the surface of plate 30 is treated with a surface chemistry which binds target ligands the ligand spots dry on the posts leaving the post top and.