pH-controlled release of substrates from mesoporous SiO2 nanoparticles gated by metal ion-dependent DNAzymes

The pH-controlled release of substrates from mesoporous SiO2 nanoparticles, MP–SiO2 NPs, is demonstrated by capping the pores with the Mg2+- or UO22+-dependent DNAzyme sequences and unlocking of the pores with Mg2+ ions or UO22+ ions at appropriate pH values. While the Mg2+-dependent DNAzyme reveals high activity at pH = 7.2, moderate activity at pH = 6.0, and it lacks activity at pH = 5.2, the UO22+-dependent DNAzyme reveals high activity at pH = 5.2, moderate activity at pH = 6.0, and it is catalytically inactive at pH = 7.2. Accordingly, the MP–SiO2 NPs were loaded with methylene blue, MB+, or thionine, Th+, and locked in the pores by the Mg2+- and UO22+-dependent DNAzyme sequences, respectively. The pH-programmed release of MB+ or Th+ from the loaded NPs proceeds, in the presence of Mg2+ ions or UO22+ ions, at pH = 7.2 and pH = 5.2, using the Mg2+- and UO22+-dependent DNAzyme as catalysts that cleave the protecting caps and unlock the pores, respectively. At pH = 6.0 the MB+- and Th+-loaded NPs are concomitantly unlocked by the two DNAzymes. The unlocking processes are selective and other metal ions do not stimulate the release processes.