Synthesis of nanoporous silica nanoparticles encapsulating porphyrin derivatives by non-surface-protected hot water etching for their fluorescent sensing of metal ions in water

Abstract

Nanoporous silica nanoparticles (SiO₂ NPs) encapsulating porphyrin derivatives were synthesized by non-surface-protected hot water etching and their metal ion detection by fluorescence quenching was examined in water. First, an alkoxysilyl group was introduced to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) by its reaction with 3-(triethoxysilyl)propyl isocyanate, then the porphyrin was used in a modified Stöber method to yield SiO₂ NPs incorporating TAPP chemically bound within the particles. The porphyrin-modified SiO₂ NPs (TAPP@SiO₂ NPs) dispersed well in water despite the high hydrophobicity of TAPP. The amount of TAPP incorporated in the SiO₂ NPs was influenced by the reaction temperature of the modified Stöber method used. Finally, TAPP@SiO₂ NPs were converted to nanoporous porphyrin-modified SiO₂ NPs (TAPP@E-SiO₂ NPs) by non-surface-protected hot water etching. The TAPP fluorescence was enhanced by the silica layer porosification, suggesting greater penetration of excitation light into the TAPP@E-SiO₂ NPs. Evaluation of TAPP@E-SiO₂ NPs fluorescence sensitivity towards metal ions in water demonstrated high Cu²⁺ selectivity with a limit of detection of 27 μM.