The unique capability of fullerene (C-60) to absorb light and generate reactive oxygen species (ROS) has been extensively studied for photosensitized water treatment and cancer therapy. Various material synthesis strategies have been proposed in parallel to overcome its intrinsic hydrophobicity and to enhance availability in water and physiological media. We present here a strikingly simple approach to make C-60 available to these applications by hand-grinding dry C-60 powder with nanodiamond (ND) using a mortar and pestle. The resulting ND-C-60 composite was found to form a stable aqueous colloidal suspension and efficiently drive photosensitized production of ROS under visible light illumination. ND-C-60 rapidly adsorbed and oxidized organic contaminants by photogenerated ROS. In the experiments for photodynamic cancer therapy, ND-C-60 was internalized by cancer cells and induced cell apoptosis without noticeable toxicity. Treatment of tumor-bearing mice with ND-C-60 and light irradiation resulted in tumor shrinkage and prolonged survival time. (c) 2020 Elsevier Inc. All rights reserved.