a method for linking strongly negatively charged biological macromolecules like deoxyribonucleic acid , ribonucleic acid and glycosaminoglycans to plastic substrates , comprising contacting the macromolecules and the plastics with a non chaotropic solution containing a salt in an amount of at least 20 % of its saturation concentration , or having a ph below the pka of the charged groups of the macromolecules to be linked . also disclosed are the products of the method , in particular a microtiter plate with plastic wells coated with the negatively charged non - proteinaceous macrobiomolecules .