In this article, pH-responsive near-infrared emitting conjugated polymer nanoparticles (CPNs) are prepared, characterized, and their stabilities are investigated under various conditions. These nanoparticles have capacity to be loaded with water insoluble, anticancer drug, camptothecin (CPT), with around 10% drug loading efficiency. The in vitro release studies demonstrate that the release of CPTs from CPNs is pH-dependent such that significantly faster drug release at mildly acidic pH of 5.0 compared with physiological pH 7.4 is observed. Time and dose-dependent in vitro cytotoxicity tests of blank and CPT-loaded nanoparticles are performed by real-time cell electronic sensing (RT-CES) assay with hepatocellular carcinoma cells (Huh7). The results indicate that CPNs can be effectively utilized as vehicles for pH-triggered release of anticancer drugs. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 114-122