Nanoshell-mediated color tuning of erbium-sensitized upconversion nanoparticles for advanced phototherapy above 1500 nm

Abstract

Conventional phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), is often limited by the risk of serious photodamage and shallow tissue caused by the excitation light. Lanthanide-doped upconversion nanoparticles (UCNPs) enable to convert long-wavelength light to short-wavelength emission, which, in principle, can address these issues in phototherapy. However, traditional UCNPs are mainly excitable in the near-infrared I region (700–900 nm), which still faces challenges such as strong light absorption/scattering and overheating side effects. Herein, we have developed an Er³⁺-sensitized upconversion nanoparticle (NaErF₄@NaYbF₄@NaYF₄) in response to 1550 nm excitation light in the far NIR-II region. Through a core–shell–shell engineering strategy, the emissive signal of Er³⁺ ion can be finely tailored from red-dominant to green-dominant, offering great flexibility in optical tuning of Er³⁺ sensitized UCNPs under 1550 nm light excitation. Upon surface modification by a mesoporous silica shell and loading of dual photosensitive agents (MC540 (merocyanine 540) and FePc (iron phthalocyanine)), a synergistic PDT/PTT phototherapeutic nanoagent was constructed. Results showed that as-developed nanotherapeutic platform could solve the overheating problem and further enhance tissue penetration upon illumination by 1550 nm light, thus demonstrating great efficiency of combinational PDT/PTT for tumor treatment.