Lanthanide-doped nanoparticles (LnNPs) can harvest the near-infrared (NIR) light to emit higher energy photons (upconversion) or lower energy photons (downshifting). In a recent study published in ACS Nano, a team led by Prof. CHANG Yulei from Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences developed a novel photoswitchable nanoparticle based on LnNPs for antitumor application, which had UV-blue and NIR-IIb (1525 nm) emission upon 980 nm laser, and 1525 nm emission upon 800 nm laser. The above nanoparticles were further used for achieving real-time NIR-IIb (800 nm) imaging-guided photodynamic therapy (PDT) (980 nm).

Photoswitchable materials have important application prospects in the fields such as high-density optical data storage, optoelectronic devices, sensing, and biomedicine. In 2018, Prof. CHANG's team developed a photoswitchable upconversion nanoparticle which carried out the upconversion emission-based decoupling phototheranostics. This nanoparticle can emit red fluorescence for imaging upon 800 nm laser and emit UV-blue fluorescence for PDT upon 980 nm laser and this study confirmed the ability of the imaging-guided “off-on” therapy based on the photoswitchable nanoparticle.

Compared with the previous use of upconversion red light for real-time imaging, NIR-IIb (1525 nm) imaging can provide deeper tissue penetration depth, lower scattering, etc., which further improves the clarity of imaging.

To obtain more comprehensive tumor information, magnetic resonance imaging (MRI) was introduced into the nanoplatform through coating pH-sensitive calcium phosphate (CaP) doped with Mn2+. This structure could enhance the T1-MRI signal because Mn2+ ions would be released from CaP in tumor microenvironment (TME) which could establish the enhanced-MRI nanoplatform with a strong optical signal.

In addition, PDT combined with doxorubicin (a chemotherapeutic drug) could improve the tumor therapeutic effect, especially immunogenic cell death (ICD). The results showed significant antitumor and metastasis inhibition effects in vitro and in vivo.

This study provides a new strategy of precise tumor phototheranostics.