Simultaneous imaging and photodynamic-enhanced photothermal inhibition of cancer cells using a multifunctional system combining indocyanine green and polydopamine-preloaded upconversion luminescent nanoparticles

This work introduces a novel multifunctional system called UPIPF (upconversion-polydopamine-indocyanine-polyethylene-folic) for upconversion luminescent (UCL) imaging of cancer cells using near-infrared (NIR) illumination. The system demonstrates efficient inhibition of human hepatoma (HepG2) cancer cells through a combination of NIR-triggered photodynamic therapy (PDT) and enhanced photothermal therapy (PTT). Initially, upconversion nanoparticles (UCNP) are synthesized using a simple thermal decomposition method. To improve their biocompatibility and aqueous dispersibility, polydopamine (PDA) is introduced to the UCNP via a ligand exchange technique. Indocyanine green (ICG) molecules are electrostatically attached to the surface of the UCNP-polydopamine (UCNP@PDAs) complex to enhance the PDT and PTT effects. Moreover, polyethylene glycol (PEG)-modified folic acid (FA) is incorporated into the UCNP-polydopamine-indocyanine-green (UCNP@PDA-ICGs) nanoparticles to enhance their targeting capability against cancer cells. The excellent UCL properties of these UCNP enable the final UCNP@PDA-ICG-PEG-FA nanoparticles (referred to as UPIPF) to serve as a potential candidate for efficient anticancer drug delivery, real-time imaging, and early diagnosis of cancer cells. Furthermore, the UPIPF system exhibits PDT-assisted PTT effects, providing a convenient approach for efficient cancer cell inhibition (more than 99% of cells are killed). The prepared UPIPF system shows promise for early diagnosis and simultaneous treatment of malignant cancers.