Increasing binding density of yeast cells by control of surface charge with allylamine grafting to ion modified polymer surfaces

•Allylamine reacts with free radicals on plasma implanted polymer surfaces.•The reactions increase the surface roughness and alter surface chemistry.•Surface charge is less negative after allylamine treatment.•Yeast cells attach with higher density on allylamine treated surface at pH 7.4. Plasma immersion ion implantation (PIII) treatment of polymers creates a biointerface capable of direct covalent immobilization of biomolecules. The immobilization of protein molecules is achieved by covalent bonds formed between embedded radicals on the treated surface and amino acid side chains and cells can be immobilized through cell-wall proteins. The attachment density of negatively charged entities on a PIII treated surface is inhibited by its negative surface charge at neutral pH. To reduce the negative charge of PIII treated surfaces in phosphate buffer (pH 7.4, 11mM), we develop an effective approach of grafting allylamine monomers onto the treated surface. The results reveal reactions between allylamine and radicals on the PIII treated surface. One of these triggers polymerization, increasing the number of amine groups grafted. As a consequence, the PIII treated polystyrene surface after allylamine exposure becomes more hydrophobic and less negatively charged in phosphate buffer. Using yeast cells as an example, we have shown a significant improvement (6–15 times) of cell density immobilized on the PIII treated surface after exposure to allylamine.