Dual NIR-I excitation and emission-based thermometry and pH-responsive drug delivery using NaYF4:Yb,Er@SiO2-folic acid conjugates.

The development of multifunctional host materials capable of simultaneous diagnostics and therapy holds significant promise for biomedical applications. Here, we report the synthesis of NaYF4:Yb,Er particles with cuboidal morphology, designed for optical temperature sensing. To enable controlled drug release, the hydrophobic particles were coated with a mesoporous silica layer to enhance biocompatibility and facilitate dispersion in aqueous solutions and also allowed loading the hybrid material with drug molecules. Surface functionalization with folic acid (FA) further enhanced their potential for targeted delivery applications. Doxorubicin, a chemotherapeutic agent, was successfully loaded into the mesoporous silica shell, allowing for pH-sensitive drug release. Ratiometric upconversion luminescence in both the visible and near-infrared I (NIR-I) region allowed precise temperature monitoring under NIR excitation. The thermometric performance of this system was also evaluated in chicken breast tissue. This work highlights the potential of these hybrid particles as a versatile platform for integrated temperature sensing and drug delivery, with promising applications in theranostics.