Extracellular clustering of amyloid-β (Aβ) and an impaired autophagy lysosomal pathway (ALP) are the hallmark features in the early stages of incurable Alzheimer's disease (AD). There is a pressing need to find or develop new small molecules for diagnostics and therapeutics for the early stages of AD. Herein, we report a small molecule, namely F-SLCOOH, which can bind and detect Aβ1-42, Iowa mutation Aβ, Dutch mutation Aβ fibrils and oligomers exhibiting enhanced emission with high affinity. Importantly, F-SLCOOH can readily pass through the blood-brain barrier and shows highly selective binding toward the extracellular Aβ aggregates in real-time in live animal imaging of a 5XFAD mice model. In addition, a high concentration of F-SLCOOH in both brain and plasma of wildtype mice after intraperitoneal administration was found. The ex vivo confocal imaging of hippocampal brain slices indicated excellent colocalization of F-SLCOOH with Aβ positive NU1, 4G8, 6E10 A11 antibodies and THS staining dye, affirming its excellent Aβ specificity and targetability. The molecular docking studies have provided insight into the unique and specific binding of F-SLCOOH with various Aβ species. Importantly, F-SLCOOH exhibits remarkable anti-fibrillation properties against toxic Aβ aggregate formation of Aβ1-42, Iowa mutation Aβ, and Dutch mutation Aβ. F-SLCOOH treatment also exerts high neuroprotective functions and promotes autophagy lysosomal biogenesis in neuronal AD cell models. In summary, the present results suggest that F-SLCOOH is a highly promising theranostic agent for diagnosis and therapeutics of AD.