A facile in situ hydrophobic layer protected selective etching strategy for the synchronous synthesis/modification of hollow or rattle-type silica nanoconstructs

A novel and general in situ hydrophobic shell-protected selective etching strategy has been developed to synchronously synthesize and modify hollow mesoporous silica nanoparticles (HMSNs) and rattle-type mesoporous silica nanoparticles (RMSNs) with well-defined morphology, effectively avoiding the drawbacks of post-modification. The key point of the strategy lies in the hydrophilicity differences between the pure silica inner core and the organic hybrid silica shell, which results in the preferential etching of the pure silica inner core. Except that amino group functionalized HMSNs (amino-HMSNs) can be synthesized via this strategy, it can be readily applied for the synthesis of HMSNs and RMSNs synchronously grafted with different kinds of functional groups by employing other silane coupling agents, directly indicating the generality of this strategy. Furthermore, adding no additional reduction agents, the amino-HMSNs can be regarded as nanoreactors, and a distinctively heterogeneous rattle-type structure, Au@HMSN/Au, with an entrapped size-tunable Au nanoparticle and some small Au nanocrystals embedded in the hollow cavity and shell of each nanoparticle, respectively, is obtained. As hybrid ultrasound contrast agents (UCAs), unlike micro-sized organic UCAs merely confined to blood pool imaging, the as-synthesized nano-sized amino-HMSNs can achieve excellent in vitro ultrasound imaging, and potentially be applied in cell-level imaging. More importantly, relying on the process merits of our strategy, such as the doping of silane coupling agents and no calcination treatment, amino-HMSNs exhibit enhanced ultrasound imaging to some certain extent compared to the calcined ones.