A photosensitizer formulation can be disposed on or in a mesh; net; netting; screen; curtain of strands, fibers, or monofilaments; substrate, personal protective gear, mask, or any other suitable object. The photosensitizer formulation, when in contact with molecular oxygen and activated by light or ultrasound, produces microbicidal singlet oxygen. A variety of different arrangements and applications are described. For example, an air flow device may also be included to generate a flow of air through or over the photosensitizer formulation. A fluorescent formulation may be included to monitor photobleaching. The photosensitizer formulation may be disposed in a concentration gradient to generate antigenic particles by damaging or destroying microbes.