Hollow structured SrMoO4:Yb3+, Ln3+ (Ln = Tm, Ho, Tm/Ho) microspheres: tunable up-conversion emissions and application as drug carriers

Abstract

In this study, a facile and mild one-pot approach was employed to prepare hollow-structured SrMoO₄ spheres using soluble sodium poly(4-styrenesulfonate) (PSS) as a soft template. It is found that the as-prepared product exhibits hollow spherical morphology, good dispersity, and narrow size distribution. The formation mechanism has also been proposed. Tunable multicolor and bright white up-conversion (UC) emissions were successfully realized by precisely adjusting the doping sensitizer (Yb³⁺) and activator (Tm³⁺, Ho³⁺, and Tm³⁺/Ho³⁺) concentration in the host matrix. MTT assay shows the good biocompatibility of SrMoO₄:Yb³⁺/Tm³⁺ hollow spheres, which were used as an anti-cancer drug carrier to evaluate the loading and controlled release behavior by selecting doxorubicin hydrochloride (DOX) as a model drug. Drug release tests reveal a sustained drug release behavior and especially the UC emission intensities of the drug loaded system increase with the released amount of DOX, indicating that the extent of drug release can be monitored or tracked by the change in emission intensity. Moreover, the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carrier was investigated and the endocytosis process of drug-loaded microspheres was studied using confocal laser scanning microscopy (CLSM) and flow cytometry. Considering the good biocompatibility, high drug loading amount and obvious sustained drug release properties, the hollow microspheres are highly promising in biological areas.