pH-Responsive porphyrin-silica nanoparticles conjugate via ionic self-assembly

Ionic self-assembly (ISA) is a powerful tool that has been exploited to create various functional nanomaterials through the electrostatic interactions of different building blocks. Herein, we disclose for the first time the synthesis and characterization of benzoic acid functionalized silica nanoparticles (MSNs-Bn) and its subsequent ISA with meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) to form a pH responsive hybrid material. The resulting pH responsive conjugate is an attractive candidate as a drug delivery vehicle in which the MSNs-Bn act as a drug carrier and the TMPyP act as a capping agent for the silica nanopores. The application of these pH-responsive interactions between the negatively charged carboxylate groups on the surface of mesoporous silica nanoparticles and the positively charged porphyrin as a drug delivery system was investigated by studying the loading and release of Hoechst 33342 dye (a water-soluble biological stain with similar size to those of therapeutic drugs) in response to a pH change. The reported approach enables the delivery of a chemotherapeutic drug in addition to the TMPyP, which is also well-known as a photodynamic therapy (PDT) agent, thus paving the way for synergistic chemo-photodynamic cancer therapy. The study shows that the resulting conjugate demonstrate the drug delivery mechanism which is responsive to changing the pH values from 7.5 to 4.5, and can deliver about 2 wt% of the chemotherapeutic drug tested.