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Photo‐Induced Charge‐Variable Conjugated Polyelectrolyte Brushes Encapsulating Upconversion Nanoparticles for Promoted siRNA Release and Collaborative Photodynamic Therapy under NIR Light Irradiation

Combination of photodynamic therapy (PDT) with small interfering RNA (siRNA) therapy has become a major strategy in cancer treatment for enhancing anticancer efficacy. However, developing nanoplatform that can promote siRNA release and collaborate with efficient PDT under NIR light irradiation is still a big challenge. Photo‐induced charge‐variable conjugated polyelectrolyte brushes encapsulating upconversion nanoparticles (UCNP@CCPEB) as an efficient nanoplatform are reported. Cationic conjugated polyelectrolyte brush (CCPEB) is synthesized through quaternary ammoniation of N‐functionalized polyfluorene brush by photodegradable 2‐nitrobenzyl‐2‐bromoacetate. CCPEB with abundant positive charges and intrinsic photosensitizer (PS) performance is good for integrating siRNA carrier and PS into one molecule. The obtained CCPEB next encapsulates upconversion nanoparticle for realizing its NIR light excitation. Agarose gel electrophoresis experiments show that UCNP@CCPEB present good stability and excellent siRNA‐loading capacity (1 mol UCNP@CCPEB to at least 32.5 mol siRNA). Under 980 nm light irradiation, UCNP@CCPEB exhibit efficient single oxygen production for PDT. Concurrently, the photoresponsive cationic side‐chain of CCPEB turns into zwitterionic chain and thus accelerates its siRNA release to 80%. In vitro and in vivo experiments show that the successful A549 tumor suppression is achieved by UCNP@CCPEB/siPlk1 complex under 980 irradiation. It is envisioned that UCNP@CCPEB can serve as an efficient platform for combining various phototherapies together.