Polypyrrole-methylene blue nanoparticles as a single multifunctional nanoplatform for near-infrared photo-induced therapy and photoacoustic imaging

The combination of photothermal therapy (PTT) and photodynamic therapy (PDT) has recently gained much attention due to its selective and localized therapeutic effects by light irradiation. The reagents for phototherapy should have a large absorption coefficient in the near infrared region (NIR) (700 to 2500 nm) to maximize the depth of light penetration in tissues. In this study, we designed multifunctional nanoparticles that can provide strong NIR absorbing capability for the combined treatment of PTT and PDT. For the first time, FDA-approved photosensitizer methylene blue (MB) was conjugated with photothermal material polypyrrole (PPy) to form a novel NIR photo-absorber. The obtained PPy-MB NPs with an average size of 48.5 nm showed excellent biocompatibility, photothermal stability, and high NIR absorbance for the combined PTT and PDT. Under a NIR laser (e.g., 808 nm laser) at 0.5W cm(-2), the temperature of the aqueous solution containing 50 mg ml(-1) PPy-MB NPs reached up to 50 degrees C within a very short time and reactive oxygen species (ROS) were also generated. In vitro investigation confirmed the effectiveness of the PPy-MB NPs in killing the cancer cells under the NIR laser. Further, the phantom test of photoacoustic microscopy (PAM) used in conjunction with PPy-MB NPs showed a strong photoacoustic signal. Therefore, the novel PPy-MB NPs could be considered as promising single multifunctional nanoplatforms for further applications of photo-induced therapy and biomedical imaging.