Near-infrared (NIR) light triggered photodynamic therapy (PDT), based on upconversion nanoparticles (UCNPs), has attracted great attention because of its high tissue penetration and low photodamage to living organisms. However, most UCNPs cannot be stably dispersed in aqueous solution and cannot carry photosensitive drugs directly. Besides, UCNP mediated PDT is a fluorescence resonance energy transfer (FRET) process from the UCNPs to the attached photosensitive drugs. So the drug and UCNPs must be stably connected and close enough. In this manuscript, carboxymethyl-β-cyclodextrin (COOH-β-CD) was used to connect UCNPs and adamantine modified phthalocyanine (Ad-ZnPc) through a self-assembly process followed by a host-guest interaction. COOH-β-CD can provide good water solubility of the system and short-distance linking between the UCNPs and Ad-ZnPc. Most importantly, the system has a strong NIR light triggered PDT activity toward cancer cells.

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) 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)), 8 (ZnPc-(COOH)) and 16 (ZnPc-(COOH)) COOH groups, were synthesized. A comparison of the results indicated that ZnPc-(COOH) existed in its monomeric form under physiological conditions because of its large substituents. Moreover, ZnPc-(COOH) showed superior singlet oxygen (O) generation ability when compared to ZnPc-(COOH) and ZnPc-(COOH). Therefore, we chose ZnPc-(COOH) 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.

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