S 4500 instrument

Sodium borohydride (NaBH₄), ascorbic acid, silver nitrate (AgNO₃), tetrachloroauric acid (HAuCl₄), Thioflavin-S (ThS) and Aβ15-20 were purchased from Sigma-Aldrich. N-cetyltrimethylammonium bromide (CTAB) was obtained from Alfa Aesar. 2-aminoethanethiol was purchased from Aladdin. Aβ1-40 was obtained from American peptide. POMs were gifts from Prof. Wang. All the chemicals were used as received without further purification. Distilled water (18.2 MΩ; Millpore Co., USA) was used in all experiments and to prepare all buffers. Ultraviolet-visible spectroscopy (UV-vis) measurements were recorded on a Jasco-V550 UV-Vis spectrophotometer. To determine the composition of the as-prepared samples, in situ energy-dispersive X-ray spectroscopy (EDS) analysis were performed using a HITACHI S-4500 instrument. X-ray photoelectron spectra (XPS) were acquired on an ESCALab220i-XL electron spectrometer from VG Scientific using 300W Al Kα as the excitation source. The binding energies obtained in the XPS spectral analysis were corrected for specimen charging by referencing C1s to 284.8 eV. TEM images were recorded using a FEI TECNAI G2 20 high-resolution transmission electron microscope operating at 200 kV. The zeta potential of the nanoparticles in water was measured in a Zetasizer 3000HS analyzer.