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Near infrared (NIR) light-activated supersensitive drug release via photothermal conversion is of particular interest due to its advantages in spatial and temporal control. However, such supersensitive drug release is rarely reported for polymeric nanoparticles. In this study, polymeric nanoparticles observed with flowable core can achieve NIR-activated supersensitive drug release under the assistance of photothermal agent. It is demonstrated that only 5 s NIR irradiation (808 nm, 0.3 W cm−2) leads to 17.8% of doxorubicin (DOX) release, while its release is almost completely stopped when the NIR laser is switched off. In contrast, the control, poly( d, l-lactide) nanoparticles with rigid cores, do not exhibit such supersensitive effect. It is demonstrated that intraparticle temperature is notably increased during photothermal conversion by detecting fluorescein lifetime using a time-correlated single photon counting (TCSPC) technique, which is the main driving force for such supersensitive drug release from hydrophobic flow core. In contrast, rigid chain of nanoparticular core hinders drug diffusion. Furthermore, such NIR light-activated supersensitive drug release is demonstrated, which significantly enhances its anticancer efficacy, resulting in overcoming of the resistance of cancer cells against DOX treatment in vitro and in vivo. This simple and highly universal strategy provides a new approach to fabricate NIR light-activated supersensitive drug delivery systems. [ABSTRACT FROM AUTHOR]