Lead/cadmium-free near-infrared multifunctional nanoplatform for deep-tissue bimodal imaging and drug delivery

Well-designed multifunctional nanoplatforms integrating diagnosis and therapy capabilities are of significant importance in the emerging research area of theranostics, which is expected to have great impact on future medicine. Herein, we rationally designed and engineered a multifunctional NaGdF4:Nd3+@mSiO2 nanoplatform by loading ultrasmall NaGdF4:Nd3+ nanoparticles (∼4.1 nm in diameter) into relatively large-channel mesoporous SiO2 (mSiO2) nanospheres for the first time. Thanks to the unique combination of paramagnetic property, and the capability of being excited by near infrared (NIR) light in the first biological window (NIR-I: 700–950 nm) and emitting in the second biological window (NIR-II: 1000–1350 nm) in single-type nanoparticles of NaGdF4:Nd3+, the NaGdF4:Nd3+@mSiO2 nanoplatform realizes magnetic resonance and NIR photoluminescence dual-mode tumor imaging of live mice. In particular, this NIR-I excitation and NIR-II emission property enables in vitro NIR porcine tissue photoluminescence imaging up to 12 mm in thickness. Moreover, the unique three-dimensional mesoporous structure of the nanoplatform allows the efficient loading of doxorubicin molecules (DOX, a commonly used drug model) at a high level and demonstrates pH-responsive drug release behavior that is beneficial for cancer-targeted therapy. More importantly, this NIR-II emitting nanoplatform does not contain toxic heavy metals of lead (Pb) and cadmium (Cd) usually found in NIR-emitting nanoparticles and further, comprises a highly biocompatible, protective SiO2 network. As a result, the NaGdF4:Nd3+@mSiO2 nanoplatform demonstrates much less cytotoxicity, as compared to the counterpart containing Pb and/or Cd-based quantum dots. All these features endow the multifunctional NaGdF4:Nd3+@mSiO2 nanoplatform great potential in simultaneous disease imaging diagnostics and therapeutics.