A simple and easily controllable immobilization method for photosensitizer dyes and the resulting photosensitizer dye nanoparticle-coated membranes (PDNMs) that generate singlet oxygen (O-1(2)) under atmospheric conditions were demonstrated. A 100% porphyrin nanoparticles layer that is less than 1 mu m thick on a membrane filter caused quantitative O-1(2) production under illumination. The thin layer promotes effective light absorption as well as significantly slowed deactivation of O-1(2) by supporting materials. Moreover, the PDNMs were highly resistant to photobleaching of dye itself.