SCN–IgG functionalized NaYF₄:Yb³⁺/(Er³⁺,Tm³⁺) upconversion nanoparticles for targeted fluorescence imaging of liver cancer cells

Lanthanide-doped upconversion nanoparticles (UCNPs) offer significant potential for bioimaging due to their ability to convert near-infrared (NIR) excitation into visible emission. In this study, NaYF₄:Yb³⁺/(Er³⁺,Tm³⁺) UCNPs were synthesized <i>via</i> a hydrothermal method and sequentially functionalized with a silica shell, amine, thiocyanate (SCN), and immunoglobulin G (IgG) to enhance their biocompatibility and targeting capabilities. Structural characterization confirmed the formation of highly crystalline β-NaYF₄ cores with uniform morphology and successful surface modification. The functionalized nanoparticles exhibited strong upconversion luminescence under 980 nm excitation, with multicolor emission dominated by red light (∼660 nm). Fluorescence microscopy and flow cytometry demonstrated selective labeling of HepG2 liver cancer cells, achieving a labeling efficiency of 18.10% for SCN-IgG-conjugated nanoparticles-significantly higher than in unmodified controls. These findings demonstrate that SCN-IgG-functionalized UCNPs are effective and selective nanoprobes for targeted fluorescence imaging and hold promise for the early diagnosis of liver cancer.