Monomer zinc phthalocyanine/upconversion nanoparticle coated with hyaluronic acid crosslinked gel as NIR light-activated drug for in vitro photodynamic therapy.

Carboxyl group modified zinc phthalocyanines (ZnPc) are classic and widely used photosensitizers (PSs) in upconversion nanoparticles (UCNPs) mediated photodynamic therapy (PDT) for tumor treatment. To improve the PDT activity of the complex system of ZnPc and UCNPs, many UCNPs with high red emission intensity were design and prepared. ZnPc-(COOH)4 tends to aggregate both in water and under physiological conditions, which can sharply decrease its PDT activity. Therefore, choosing monomeric COOH groups modified ZnPc as PSs is an alternative way to improve their activity. In this manuscript, three zinc(ii) phthalocyanines, substituted with 4 (ZnPc-(COOH)4), 8 (ZnPc-(COOH)8) and 16 (ZnPc-(COOH)16) COOH groups, were synthesized. A comparison of the results indicated that ZnPc-(COOH)16 existed in its monomeric form under physiological conditions because of its large substituents. Moreover, ZnPc-(COOH)16 showed superior singlet oxygen (1O2) generation ability when compared to ZnPc-(COOH)4 and ZnPc-(COOH)8. Therefore, we chose ZnPc-(COOH)16 as PSs for absorption on the surface of the UCNPs. Then, they were encapsulated by crosslinked methacrylated hyaluronic acid (m-HA), which provides active tumor accumulation ability by binding its overexpressed receptors on the surface of cancer cells. The resulting nanoparticles can be effectively taken up by cancer cells and shows strong near-infrared (NIR) light triggered PDT in vitro.