The K+-induced formation of G-quadruplexes provides a versatile motif to lock or unlock substrates trapped in the pores of mesoporous SiO2 nanoparticles, MP-SiO2 NPs. In one system, the substrate is locked in the MP-SiO2 NPs by K+-ion-stabilized G-quadruplex units, and the pores are unlocked by the elimination of K+ ions using Kryptofix [2.2.2] (KP) or 18-crown-6-ether (CE) from the G-quadruplexes. In the second system, the substrate is locked in the pores by means of K+-stabilized aptameric G-quadruplex/thrombin units. Unlocking of the pores is triggered by the dissociation of the aptamer/thrombin complexes through the KP- or CE-mediated elimination of the stabilizing K+ ions. In the third system, duplex DNA units lock the pores of MP-SiO2 NPs, and the release of the entrapped substrate is stimulated by the K+-ion-induced dissociation of the duplex caps through the formation of the K+-stabilized G-quadruplexes. The latter system is further implemented to release the anti-cancer drug, doxorubicin, in the presence of K+ ions, from the MP-SiO2 NPs. Preliminary intracellular experiments reveal that doxorubicin-loaded MP-SiO2 NPs lead to effective death of breast cancer cells.