Fast scan afm instrument

A volume of 5 μL sample solution via different times of incubation was deposited onto a freshly cleaved mica surface for 15 minutes. Then, the sample on mica was washed twice with either Milli-Q water (for all oligomer samples) or phosphate buffer (for all hIAPP samples) and baked for 5 minutes at 65 °C in an oven to flat the lipid film. Atomic force microscopy (AFM) measurements were performed at room temperature on a Fast Scan AFM instrument (Bruker Instruments Inc., German) using tapping mode. Images were collected at a scan rate of 1 Hz and a scan angle of 0°.

All peptides were purchased from Genscript (http://www.genscript.com/) at >98% purity (HPLC purified), and all buffers were prepared in ultrapure deionized water (Millipore, Billerica, MA). For pH study, a tricomponent buffer composed of citrate, HEPES, and CHES was used (broad-range buffer CHC; Molecular Dimensions, Altamonte Springs, FL). Highly oriented pyrolytic graphite (HOPG) slabs for imaging on graphite were purchased from SPI Supplies (Structure Probe, West Chester, PA). Atomic force microscopy (AFM) imaging was performed with a FastScan AFM instrument (Bruker Instruments, Billerica, MA) using soft triangular-shaped silicon nitride cantilevers (FastScan C, Bruker Instruments) characterized by a nominal spring constant of k ∼ 0.8 N/m and a nominal resonant frequency of 300 kHz. Imaging was performed using the FastScan device’s ScanAsyst Mode at speeds of ∼4 lines/s for optimal topographic quality. For AFM imaging under fluid, we used a home-made perfusion cell that allowed the fluid medium to be refreshed.