Donor-acceptor conjugated polymer nanoparticles and nanofibers, based on Poly[4,4-bis(2-ethylhexyl)-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe), were synthesized using Pluronic F127 as a template. The nanomaterials were compared to previously reported PCPDTBSe nanoparticles, which were synthesized without the use of a template. Our goal was to improve on the aqueous stability and photothermal heating efficiency of the previously synthesized PCPDTBSe nanoparticles by decreasing their size and coating them with a biocompatible surfactant. The pluronic wrapped PCPDTBSe (PW-PCPDTBSe) nanoparticles (40-60 nm) showed excellent aqueous stability compared to the PW-PCPDTBSe nanofibers (d=20-60 nm, l=200-1000 nm) and previously synthesized PCPDTBSe nanoparticles (150 nm). Under stimulation from 800 nm near infrared light (3 W, 1 min), the PW-PCPDTBSe nanoparticles showed greater heat generation (T=47 degrees C) compared to bare PCPDTBSe nanoparticles and PW-PCPDTBSe nanofibers (T=35 degrees C for both). Cytotoxicity studies determined that both the PW-PCPDTBSe nanoparticles and PW-PCPDTBSe nanofibers displayed no significant toxicity toward either noncancerous small intestinal cells (FHs 74 Int) or colorectal cancer cells (CT26). Photothermal ablation studies confirmed that both the PW-PCPDTBSe nanoparticles and the PW-PCPDTBSe nanofibers can be used as localized photothermal agents to eradicate colorectal cancer cells due to their excellent ablation efficiency (>95% cell death at 15 mu g/mL concentration). (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1622-1632