A novel proton-fueled molecular gate-like delivery system has been constructed for controlled cargo release using i-motif quadruplex DNA as caps onto pore outlets of mesoporous silica nanoparticles. Start from simple conformation changes, the i-motif DNA cap can open and close the pore system in smart response to pH stimulus. Importantly, the opening/closing and delivery protocol is highly reversible and a partial cargo delivery can be easily controlled at will. A pH-switchable nanoreactor has also been developed to validate the potential of our system for on-demand molecular transport. This proof of concept might open the door to a new generation of carrier materials and could also provide a general route to use other functional nucleic acids/peptide nucleic acids as capping agents in the fields of versatile controlled delivery nanodevices.

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.[1] To date, several MSPbased controlled-release systems have been synthesized by using different kinds of capping agents including organic molecules, [2] nanoparticles, [3] and supramolecular assemblies.[4] "On-demand" release systems that respond to a range of stimuli, including redox, [2b, 4a, 5] pH or temperature, [6] enzymes, [7] competitive binding, [8] and photoirradiation [2a, 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 [7] or carbohydrates, [10] 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.[11] 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 channels. The duplex DNA cap could be either denatured by heating or hydrolyzed by endonucleases, thus opening the nanopores and releasing the cargo. As a proof-of-principle experiment, rhodamine B was chosen as model molecule and deoxyribonuclease I (DNase I) was utilized as a representative endonuclease for DNA degradation. The opening of the capped system was tested by measuring the stimuli-triggered dye release from the MSPs. Importantly, we have demonstrated the successful loading of anticancer drugs camptothecin (CPT) and floxuridine (FUDR) into MSPs, and efficient intracellular controlled drug delivery in human cancer cells when endogenous nuclease was used as a stimulus.MCM-41 silica nanoparticles were prepared by following a base-catalyzed sol-gel procedure, [12] and the resulting porous silica nanoparticles (100 nm in diameter) that contain hexagonally arranged...

An enzyme responsive nanoparticle system that uses a DNA-gold nanoparticle (AuNP) assembly as the substrate has been developed for the simple, sensitive, and universal monitoring of restriction endonucleases in real time. This new assay takes advantage of the palindromic recognition sequence of the restriction nucleases and the unique optical properties of AuNPs and is simpler than the procedure previously described by by Xu et al. (Angew. Chem. Int. Ed. Engl. 2007, 46, 3468-3470). Because it involves only one type of ssDNA modified AuNPs, this assay can be directed toward most of the endonucleases by simply changing the recognition sequence found within the linker DNA. In addition, the endonuclease activity could be quantitatively analyzed by the value of the reciprocal of hydrolysis half time (t(1/2)(-1)). Furthermore, our new design could also be applied to the assay of methyltransferase activity since the methylation of DNA inhibits its cleavage by the corresponding restriction endonuclease, and thus, this new methodology can be easily adapted to high-throughput screening of methyltransferase inhibitors.