Red emitting conjugated polymer based nanophotosensitizers for selectively targeted two-photon excitation imaging guided photodynamic therapy.

Two-photon excitation (2PE) photodynamic therapy (PDT) is a non-invasive technique for the treatment of cancer. However, its clinical applications are limited by small two-photon absorption cross section values of conventional photosensitizers. Here we designed multifunctional conjugated polymer based nanoparticles consisting of a conjugated polymer, a photosensitizer and a red-emitting dye, which can realize simultaneous 2PE red emission imaging and 2PE-PDT activities. The working principle is based on a 2PE fluorescence resonance energy transfer strategy from the conjugated polymer to photosensitizing and imaging agents. In these nanoparticles (NPs), the conjugated polymer, PPBF, was chosen as a two-photon light-harvesting material while the photosensitizer (tetraphenylporphyrin, TPP) and the red-emitting dye (TPD) were chosen as energy acceptors. The 2PE emission of TPP and TPD was enhanced by up to ∼161 and ∼23 times, respectively. The 2PE-PDT activity of these NPs was significantly improved compared with those NPs without PPBF by up to ∼149 times. Further surface-functionalization with folic acid (FA) groups allows these nanoparticles to exhibit selective affinity toward KB cancer cells. These NPs could act as novel 2PE conjugated polymer based nanoparticles combined with the advantages of low dark cytotoxicity, selective targeting and imaging-guided 2PE-PDT activities.