A reversible molecule-gated system using mesoporous silica nanoparticles functionalized with K+-stabilized G-rich quadruplex DNA

This paper proposed a novel and reversible molecule-gated system consisting of mesoporous silica nanoparticles (MSN) functionalized on the pore outlets with a G-rich quadruplex DNA (GQDNA). In this system, K+-stabilized GQDNA as a molecular switch was grafted onto the MSN surface through the covalent cross-linking approach. In the absence of silver ion (Ag+), GQDNA could fold into a quadruplex structure through π–π stacking between G–G pairs mediated by potassium ions (K+), thus blocking the pore outlets and inhibiting the release of entrapped guest molecules. In the presence of Ag+, the Ag+ can interact with G bases, leading to the unfolded GQDNA and subsequently opened pores. Interestingly, the opened pore mouths can be closed again by introducing glutathione (GSH) molecules, which can bind competitively with Ag+ ions by the thiols to result in the conformation transition of DNA from unfolded structures to quadruplex structures. By the simple conformational changes of GQDNA gatekeepers, the molecular gate can switch reversibly by the alternate addition of Ag+ ions and GSH molecules. As a proof-of-concept, Ru(bipy)32+, a strong fluorescence dye molecule, was loaded into GQDNA grafted MSN (MSN-Ru-GQDNA). The result showed that the MSN-Ru-GQDNA has a highly reversible ability to open/close pores which was proved by the released percentage of Ru(bipy)32+. With these excellent features, the release of Ru(bipy)32+ can be easily controlled at will. We believed that further developments of this reversible molecule-gated system will provide a promising nanodevice for on-demand molecular transport.