Enantiomeric carbon dots (C-dots) synthesized from l-lysine or d-lysine, modulate aggregation and cytotoxicity of amyloid beta-42 (Aβ42), the primary constituent of the amyloid plaques associated with Alzheimer's disease. In particular, l-Lys-C-dots dramatically remodeled Aβ42 secondary structure and fibril morphologies, as well as inhibited Aβ42 cytotoxicity and membrane interactions. © The Royal Society of Chemistry.