Dual-Shell Fluorescent Nanoparticles for Self-Monitoring of pH-Responsive Molecule-Releasing in a Visualized Way.

The rational design and controlled synthesis of a smart device with flexibly tailored response ability is all along desirable for bioapplication but long remains a considerable challenge. Here, a pH-stimulated valve system with a visualized “on–off” mode is constructed through a dual-shell fluorescence resonance energy transfer (FRET) strategy. The dual shells refer to carbon dots and fluorescent molecules embedded polymethacrylic acid (F-PMAA) layers successively coating around a SiO2 core (ca. 120 nm), which play the roles as energy donor and acceptor, respectively. The total thickness of the dual-shell in the solid composite is ca. 10 nm. The priorities of this dual-shell FRET nanovalve stem from three facts: (1) the thin shell allows the formation of efficient FRET system without chemical bonding between energy donor and acceptor; (2) the maximum emission wavelength of CD layer is tunable in the range of 400–600 nm, thus providing a flexible energy donor for a wide variety of energy acceptors; (3) the...