Figure 2.

A graphical representation of the pH-responsive MSNP nanovalve.

Notes: (A) Synthesis of the stalk, loading of the cargo, capping of the pore, and release of the cap under acidic conditions. The average nanopore diameter of the MSNP is ~2.2 nm and the periphery diameter of the secondary side of β-cyclodextrin is ~1.5 nm. Thus, for a cargo with a diameter >0.7 nm, a single nanovalve should be adequate to achieve effective pH-modulated release. (B) Details of the protonation of the stalk and release of the β-cyclodextrin. (C) TEM image of capped MSNP. The scale bar is 10 nm. Reprinted with permission from Meng H, Xue M, Xia T, et al. Autonomous in vitro anticancer drug release from mesoporous silica nanoparticles by pH-sensitive nanovalves. J Am Chem Soc. 2010;132(36):12690–12697. Copyright 2010 American Chemical Society.⁵⁹

Abbreviations: TEM, transmission emission tomography; β-CD, β-cyclodextrin; MSNP, Mesoporous silica nanoparticle, MBI, 1-Methyl-1H-benzimidazole.