NIR-responsive upconversion nanoplatforms: an anionic drug carrier for ROS amplification induced by β-amyloid fibrils

Alzheimer's disease (AD), marked by the misfolding/aggregation of β-amyloid (Aβ), is a major global health challenge. Polyoxometalates (POMs), as anionic therapeutic agents, exhibit potential in depolymerizing Aβ fibrils, inhibiting Aβ fibrillation, and acting as a photocatalyst. To achieve targeted reactive oxygen species (ROS) amplification, we developed a chitosan-modified near-infrared (NIR)-responsive upconversion nanoplatform, UCNPs(Tm/Er)@SiO₂@GPS@CH, as a targeted carrier for POMs. The nanoplatform was constructed by sequentially modifying upconversion nanoparticles (UCNPs) with a silica layer, 3-glycidoxypropyltrimethoxysilane (GPS, as a linker), and chitosan (CH, a cationic biomacromolecule). The cationic CH layer enabled efficient loading of anionic POMs through electrostatic interactions with an optimal POM loading capacity of 415.41 μg mg^-1 that positively correlated with CH modification levels. Under NIR irradiation, the nanoplatform triggered a photodynamic effect with abundant ROS. Notably, compared with the control group and Aβ monomer group, the ROS generation in the Aβ fibril group was approximately doubled, which further enhanced the targeted therapeutic efficacy of the system. By integrating NIR responsiveness, cationic chitosan, targeted ROS generation, and low systemic toxicity, the nanoplatform provides a novel strategy for the photooxidative treatment of AD and offers insights into the design of chitosan-modified upconversion nanoparticle-based drug carrier systems.