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Polyvalent nucleic acid/mesoporous silica nanoparticle conjugates: dual stimuli-responsive vehicles for intracellular drug delivery.

The distinctive characteristics of mesoporous silica nanoparticles (MSPs) such as thermal stability, tunable pore sizes, large load capacity, and the ease of surface functionalization make these scaffolds ideal for the design of nanodevices and “on-command” delivery applications. To date, several MSPbased controlled-release systems have been synthesized by using different kinds of capping agents including organic molecules, nanoparticles, and supramolecular assemblies. “On-demand” release systems that respond to a range of stimuli, including redox, 4a,5] pH or temperature, enzymes, competitive binding, and photoirradiation 4b,9] have recently been reported. Despite these burgeoning achievements, many of the existing capping systems have disadvantages such as the use of stimuli that are complicated and/or difficult to apply, poor applicability in aqueous solutions and biocompatibility, and the toxicity of the capping agents used. In particular, regardless of recent reports on capped MSPs that can be uncapped by certain enzymes or carbohydrates, the utility of MSP-based devices involving biomolecules for real delivery systems is still in its infancy. Therefore, the search for effective systems that, in particular, respond to internal biological stimuli still remains a big challenge in this field. Herein we describe the design and construction of a stimuli-responsive vehicle for intracellular drug delivery using a polyvalent nucleic acid/MSP “click” conjugate that responds to both external and endogenous activation. Nucleic acids have been recognized as attractive building blocks for nanotechnology and materials science owing to the remarkable specificity and versatility of these units. The unique structural motif and self-recognition properties of duplex DNA, including temperature-dependent assembly, as well as the enzymatic recognition of specific encoded bases, may be applied as triggers for functional DNA manipulation. As shown in Figure 1, self-complementary duplex DNA was anchored to the openings of the MSPs and was utilized as a cap for trapping the guest molecules within the porous