Near-infrared light activated photodynamic therapy of THP-1 macrophages based on core-shell structured upconversion nanoparticles

Upconversion nanoparticles (UCNPs) with fascinating properties hold great potential as nanotransducers for solving the light penetration problem that traditional photodynamic therapy (PDT) is facing. In this report, the synthesis and utility of UCNPs/silica core-shell structured nanoparticles for upconversion (UC) PDT and imaging of THP-1 macrophages were described. The UCNPs (NaYF₄:Yb, Er) with a uniform diameter of 28 ± 1 nm were synthesized as core and 10 nm thick biocompatible mesoporous silica was coated as shell. Photosensitizer (PS) was covalently grafted inside mesoporous silica shell. Upon excitation, NIR light is converted into visible one by UCNPs for the absorption of PS to generate singlet oxygen for killing THP-1 macrophages and inhibiting the development of atherosclerosis. The fluorescence images showed the resulting nanoparticles are readily taken up by macrophages and TEM results indicated that they are highly phototoxic. The statistical in vitro results revealed PDT could cause the apoptosis of THP-1 macrophages with a remarkable therapeutic efficacy of cell inhibition ratio of 40%.