The self-assembly of amyloidogenic peptides into -sheet-rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimer's disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid-associated neurotoxicity. This study reports that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimer's -amyloid (A) self-assembly and function as a -sheet breaker disintegrating preformed A aggregates. This study synthesizes CDs using ammonium citrate through one-pot hydrothermal treatment and passivates their surface with branched polyethylenimine (bPEI). The bPEI-coated CDs (bPEI@CDs) exhibit hydrophilic and cationic surface characteristics, which interact with the negatively charged residues of A peptides, suppressing the aggregation of A peptides. Under light illumination, bPEI@CDs display a more pronounced effect on A aggregation and on the dissociation of -sheet-rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. The light-triggered attenuation effect of A aggregation using a series of experiments, including photochemical and microscopic analysis, is verified. Furthermore, the cell viability test confirms the ability of photoactivated bPEI@CDs for the suppression of A-mediated cytotoxicity, indicating bPEI@CDs' potency as an effective anti-A neurotoxin agent.