Large-Pore Mesoporous-Silica-Assisted synthesis of high-performance ZnGa₂O₄:Cr³⁺/Sn⁴⁺@MSNs multifunctional nanoplatform with optimized optical probe mass ratio and superior residual pore volume for improved bioimaging and drug delivery

Featured with excellent biocompatibility and background-free biomedical imaging, near infrared persistent luminescence (NIR-PersL) nanomaterials synthesized by mesoporous silica nanoparticles (MSNs) template have captured increasing attentions to be as a tumor theranostic nanoplatform. Unfortunately, many researches in the past decades have mainly focused on bioimaging performance of NIR-PersL nanomaterials themselves but not synergistically on tailoring the pore volume of the MSNs to optimize the drug loading/releasing performance, which greatly limits their potential application in tumor theranostics. In this work, we propose a tailorable large-pore mesoporous-silica-assisted synthesis strategy to synthesize a series of ZnGa₂O₄:Cr³⁺/Sn⁴⁺@MSNs (ZGOCS@MSNs) NIR-PersL nanospheres as nanoplatform. The ZGOCS@MSNs possess average diameters of ~ 80 nm. More interestingly, the mass ratio of ZGOCS to MSNs (MRZM) increases with the increasing of pore sizes of MSNs and the NIR-PersL performances of ZGOCS@MSNs enhance with the increase of MRZM, suggesting that MRZM plays an important role in optimizing NIR-PersL performance of the nanospheres. In vitro and in vivo NIR-PersL imaging further confirm the MRZM-dependent performance enhancement in NIR-PersL nanospheres. More importantly, the employment of large pore MSNs maintains the mesoporous structure of NIR-PersL nanospheres and the residual pore volume of ZnGa₂O₄:Cr³⁺/Sn⁴⁺@MSNs is high enough and available for efficient drug loading/releasing. Benefited from excellent rechargeable tumor NIR-PersL imaging ability and large residual cavities, ZGOCS@MSNs show high dose (~53%) of loading DOX and exhibit outstanding cancer cell killing efficiency, implying the MRZM also plays an important role in optimizing the drug loading/releasing performance of the nanospheres. In summary, the as-synthesized high performance ZnGa₂O₄:Cr³⁺/Sn⁴⁺@MSNs bi-functional nanoplatform showcases its great potential for imaging-guided cancer chemotherapy. We expect our work could take the development of NIR-PersL-based theranostic nanoplatforms a step forward.