Poly(Acrylic Acid) Modification of Nd3+-Sensitized Upconversion Nanophosphors for Highly Efficient UCL Imaging and pH-Responsive Drug Delivery

In this work, a simple method is demonstrated for the synthesis of multifunctional core-shell nanoparticles NaYF4:Yb,Er@NaYF4:Yb@NaNdF4:Yb@NaYF4:Yb@PAA (labeled as Er@Y@Nd@Y@PAA or UCNP@PAA), which contain a highly effective 808-nm-to-visible UCNP core and a thin shell of poly(acrylic acid) (PAA) to achieve upconversion bioimaging and pH-sensitive anticancer chemotherapy simultaneously. The core-shell Nd3+-sensitized UCNPs are optimized by varying the shell number, core size, and host lattices. The final optimized Er@Y@Nd@Y nanoparticle composition shows a significantly improved upconversion luminescence intensity, that is, 12.8 times higher than Er@Y@Nd nanoparticles. After coating the nanocomposites with a thin layer of PAA, the resulting UCNP@PAA nanocomposite perform well as a pH-responsive nanocarrier and show clear advantages over UCNP@mSiO(2), which are evidenced by in vitro/in vivo experiments. Histological analysis also reveals that no pathological changes or inflammatory responses occur in the heart, lungs, kidneys, liver, and spleen. In summary, this study presents a major step forward towards a new therapeutic and diagnostic treatment of tumors by using 808-nm excited UCNPs to replace the traditional 980-nm excitation.