A highly water-soluble triblock conjugated polymer for in vivo NIR-II imaging and photothermal therapy of cancer
Applications of the second near infrared (NIR) optical window (NIR-II, 1000–1700 nm) have received increasing attention with respect to reduced scattering and negligible auto-fluorescence, thus achieving a high signal-to-background ratio for pinpointing tumors compared with NIR-I imaging. Conjugated polymers have been applied in NIR-II imaging for their advantages, such as high molar extinction coefficient, wide emission wavelength, and ease of preparation. However, currently available conjugated polymer NIR-II agents suffer from a lack of water solubility. Hence, a highly water-soluble triblock conjugated polymer (POEGMA-b-PDPP-b-POEGMA) based on diketopyrrolopyrrole was successfully prepared with a high yield. The NIR-II imaging depth of the conjugated polymer was ∼7 mm, which is far beyond conventional NIR-I agents. Furthermore, the fluorescence quantum yield (QY) of POEGMA-b-PDPP-b-POEGMA reached up to 1.0%, which is higher than most reported NIR-II probes. This novel NIR-II conjugated polymer shows improved solubility (>10 mg mL−1) and greater dispersion in aqueous solution compared to those conventional conjugated polymers, due to the introduction of the water-soluble polymer POEGMA. With the help of high emission (>1000 nm), POEGMA-b-PDPP-b-POEGMA could efficiently realize the highly penetrable NIR-II imaging of tumors. In addition, POEGMA-b-PDPP-b-POEGMA could be a promising photothermal therapy agent to ablate tumors due to its high photothermal conversion efficiency (52%).