Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

<jats:title>Abstract</jats:title><jats:p>Multifunctional nanocarriers based on the up‐conversion luminescent nanoparticles of NaYF<jats:sub>4</jats:sub>:Yb<jats:sup>3+</jats:sup>/Er<jats:sup>3+</jats:sup> core (UCNPs) and thermo/pH‐coupling sensitive polymer poly[(<jats:italic>N</jats:italic>‐isopropylacrylamide)‐<jats:italic>co</jats:italic>‐(methacrylic acid)] (P(NIPAm‐<jats:italic>co</jats:italic>‐MAA)) gated mesoporous silica shell are reported for cancer theranostics, including fluorescence imaging, and for controlled drug release for therapy. The as‐synthesized hybrid nanospheres UCNPs@mSiO<jats:sub>2</jats:sub>‐P(NIPAm‐<jats:italic>co</jats:italic>‐MAA) show bright green up‐conversion fluorescence under 980 nm laser excitation and the thermo/pH‐sensitive polymer is active as a “valve” to moderate the diffusion of the embedded drugs in‐and‐out of the pore channels of the silica container. The anticancer drug doxorubicin hydrochloride (DOX) can be absorbed into UCNPs@mSiO<jats:sub>2</jats:sub>‐P(NIPAm‐<jats:italic>co</jats:italic>‐MAA) nanospheres and the composite drug delivery system (DDS) shows a low level of leakage at low temperature/high pH values but significantly enhanced release at higher temperature/lower pH values, exhibiting an apparent thermo/pH controlled “on‐off” drug release pattern. The as‐prepared UCNPs@mSiO<jats:sub>2</jats:sub>‐P(NIPAm‐<jats:italic>co</jats:italic>‐MAA) hybrid nanospheres can be used as bioimaging agents and biomonitors to track the extent of drug release. The reported multifunctional nanocarriers represent a novel and versatile class of platform for simultaneous imaging and stimuli‐responsive controlled drug delivery.</jats:p>