We present here environmental factors including pH shifts, temperature, and metal ions surrounding Aβ40 monomer to precede the oligomers. We also suggest a new idea to detect Aβ40 oligomers with anti-Aβ40 monoclonal antibody using enzyme-linked immunosorbent assay. This method involves the different sensitivity of the thermal shifts between Aβ40 monomer and the oligomers. The idea is useful for the diagnostics of Alzheimer's disease to detect Aβ40 oligomers in the serum from the patients.