Liraglutide-Conjugated Poly(methyl vinyl ether-alt-maleic acid)-Coated Core-Shell Upconversion Nanoparticles for...

In the diagnostics of diabetes, specific targeting of drugs (e.g., liraglutide) to insulin-deficient β-cells with their simultaneous noninvasive imaging is currently needed. In this report, liraglutide (LGL)-conjugated poly(methyl vinyl ether-alt-maleic acid) (PMVEMA)-coated core-shell NaYF₄:Yb,Er,Fe@NaYF₄:Nd upconversion nanoparticles (CS-UCNPs) have been developed, thoroughly physicochemically characterized, and evaluated in vivo. Novel codoping of Fe²⁺, Yb³⁺, and Er³⁺ ions in the host NaYF₄ induced upconversion emission in the red region at both 980 and 808 nm excitation, making the particles suitable for deep-tissue imaging. Surface functionalization with PMVEMA provided colloidal stability and facilitated covalent conjugation with LGL, enabling targeted binding to GLP-1 receptors on pancreatic β-cells, increasing glucose-stimulated insulin secretion from isolated Langerhans islets. Biocompatibility of CS-UCNP@PMVEMA-LGL nanoparticles was confirmed by the trypan blue dye exclusion assay. When the fluorescent dye Flamma was conjugated to the nanoparticles, in vivo fluorescence imaging revealed significantly enhanced accumulation of CS-UCNP@PMVEMA-LGL-Flamma nanoparticles in the pancreas 24 h after intramuscular injection compared with intravenous administration, with luminescence intensity approximately doubled. The improved pancreatic targeting efficiency was attributed to enhanced binding to GLP-1 receptors. Confocal microscopy and elemental analysis confirmed receptor-mediated uptake of the nanoparticles by internalization and their localization within pancreatic β-cells. These findings highlight the potential of CS-UCNP@PMVEMA-LGL nanoparticles as biocompatible targetable imaging agents with future applications in pancreatic diagnostics.