This article presents the development and characterization of nanoparticles loaded with methylene blue (MB), which are designed to be administered to tumor cells externally and deliver singlet oxygen (¹O₂) for photodynamic therapy (PDT), i.e. cell kill via oxidative stress to the membrane. We demonstrated the encapsulation of MB, a photosensitizer (PS), in three types of sub-200 nm nanoparticles, composed of polyacrylamide, sol–gel silica and organically modified silicate (ORMOSIL), respectively. Induced by light irradiation, the entrapped MB generated ¹O₂, and the produced ¹O₂ was measured quantitatively with anthracene-9,10-dipropionic acid, disodium salt, to compare the effects of different matrices on ¹O₂ delivery. Among these three different kinds of nanoparticles, the polyacrylamide nanoparticles showed the most efficient delivery of ¹O₂, but its loading of MB was low. In contrast, the sol–gel nanoparticles had the best MB loading but the least efficient ¹O₂ delivery. In addition to investigating the matrix effects, a preliminary in vitro PDT study using the MB-loaded polyacrylamide nanoparticles was conducted on rat C6 glioma tumor cells with positive photodynamic results. The encapsulation of MB in nanoparticles should diminish the interaction of this PS with the biological milieu, thus facilitating its systemic administration. Furthermore, the concept of the drug-delivering nanoparticles has been extended to a new type of dynamic nanoplatform (DNP) that only delivers ¹O₂. This DNP could also be used as a targeted multifunctional platform for combined diagnostics and therapy of cancer.