Multifunctional NaGdF₄:Nd,Yb,Ho Nanoparticles for Multimodal Bioimaging and Cellular Internalization Studies: Toward Theranostic Applications

This work developed multifunctional NaGdF₄:Nd,Yb,Ho nanoparticles for biomedical applications. Synthesized via thermal decomposition and functionalized with poly(acrylic acid) (PAA), the nanoparticles presented an average diameter of 16 nm (TEM), hexagonal crystalline structure (XRD/SAED), hydrodynamic diameter of 104 nm, and zeta potential of −36.8 mV, confirming good colloidal stability. NIR and visible luminescence arising from energy transfer processes among Nd³⁺, Yb³⁺, and Ho³⁺ enabled ratiometric luminescent nanothermometry with thermal sensitivities of 0.9% °C⁻¹ (NIR, downshifting) and 0.3% °C⁻¹ (visible, upconversion). The nanoparticles were validated as fluorescent tracers via fluorescence molecular tomography (FMT) and as positive MRI contrast agents with longitudinal relaxivity of 2.2 mM⁻¹s⁻¹. MTT cytotoxicity assays across three cell lines showed no significant cell death. Confocal fluorescence microscopy confirmed cellular internalization into GL261 cells, exploiting Ho³⁺ and Nd³⁺ visible emissions as label-free imaging signals without exogenous dyes.