Enhancing optical functionality by co-loading NaYF4:Yb,Er and CdSe QDs in a single core-shell nanocapsule

Colloidal, oil-core polymer-shell nanocapsules (NCs), loaded with both upconversion NaYF4:Yb,Er nanoparticles (NPs) and CdSe quantum dots (QDs), were prepared via nanoemulsification/solvent-evaporation methods. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques were used to comprehensively determine the structure, phase composition, and morphology of the NCs. Furthermore, we demonstrated that by simultaneously loading the hybrid fluorophores into the multimodal NCs, it is possible to combine their mechanistically distinct one- and two-photon luminescence properties. The two-photon absorption cross-section obtained at 850 nm for a single capsule was equal to 2.5 × 104 GM (Goeppert-Mayer units). Importantly, cytotoxicity studies indicated the potential of the co-encapsulated NPs and QDs for fluorescence imaging in biological specimens. We conclude that such non-toxic water-dispersible multifunctional nanohybrids represent a promising platform for advanced one- and two-photon induced fluorescence bioimaging and photonic sensing technologies.