Abstract: The present invention relates to a method of controlling microbial growth on a material or surface. The method includes applying to the material an antimicrobial agent including colloid particles having an ion exchange capacity and having attached a quantity of one or more ligands with antimicrobial properties where the quantity of ligand attached to the colloid particles is in excess of 100% and up to 200% of the ion exchange capacity of the colloid particles. The present invention also relates to a method of controlling mircobial growth in a material. In addition, the present invention relates to an antimicrobial surface, an antimicrobial material, and an antimicrobial agent.