Abstract: Methods of reducing or inhibiting growth of microbes (viruses, fungi and/or bacteria, including multi-drug resistant bacteria) can be carried out by applying a formulation including porphyrin nanoparticles to a surface to impart a residue of the porphyrin nanoparticles on the surface. The applied porphyrin nanoparticles residue can reduce or inhibit growth of infectious microbes on the surface for an extended period of time such as for at least 24 hours, 2 days, one week, etc. The applied porphyrin nanoparticles have high antimicrobial activity under visible light and without visible light.