Alzheimer’s disease (AD), an amyloid-related disease, seriously endangers the health of elderly individuals. According to current research, its main pathogenic factor is the amyloid protein, which is a kind of fibrillar aggregate formed by noncovalent self-assembly of proteins. Based on the characteristics of aggregation-induced emission (AIE), a bislactosyl-decorated tetraphenylethylene (TPE) moleculeTMNL(TPE + malononitrile + lactose), bearing two malononitrile substituents, was designed and synthesized in this work. The amphiphilicTMNLcould self-assemble into fluorescent organic nanoparticles (FONs) with near-infrared (NIR) fluorescence emission in physiological PBS (phosphate buffered saline), achieving excellent fluorescent enhancement (47-fold) upon its combination with Aβ1–42fibrils.TMNLwas successfully applied to image Aβ1–42plaques in the brain tissue of AD transgenic mice, and due to the AIE properties ofTMNL, no additional rinsing process was necessary. It is believed that the probe reported in this work should be useful for the sensitive detection and accurate localization mapping of Aβ1–42aggregates related to Alzheimer’s disease.