One-pot template-free synthesis of NaYF₄ upconversion hollow nanospheres for bioimaging and drug delivery

Hollow-structured nanomaterials with fluorescent properties are extremely attractive for image-guided cancer therapy. In this paper, sub-100 nm and hydrophilic NaYF₄ upconversion (UC) hollow nanospheres (HNSs) with multicolor UC luminescence and drug-delivery properties were successfully prepared by a facile one-pot template-free hydrothermal route using polyetherimide (PEI) polymer as the stabilizing agent. XRD, SEM, TEM, and N ₂-adsorption/desorption were used to characterize the as-obtained products. The growth mechanism of the HNSs has been systematically investigated on the basis of the Ostwald ripening. Under 980 nm excitation, UC emissions of HNSs can be tuned by a simple change of the concentration or combination of various upconverters. As a result, the PEI-coated HNSs could be used as efficient probes for in vitro upconversion luminescence (UCL) cell imaging. Furthermore, a doxorubicin storage/release behavior and cancer-cell-killing ability investigation reveal that the product has the potential to be a drug carrier for cancer therapy. One pot, zero template: Sub-100 nm NaYF₄ upconversion (UC) hollow nanospheres (HNSs) were successfully fabricated by a facile one-pot template-free synthesis route by undergoing a gas-bubble-assisted Ostwald ripening mechanism. These UC HNSs with good water solubility have low toxicity to living cells. The UC HNSs could potentially be applied for image-guided drug delivery.