Multimode picoforce system with ns 5 controller

A commercial AFM instrument (Multimode/PicoForce system with NS-V controller, Bruker Nano-surfaces, Inc. Santa Barbara, CA) was used to image air-dried nanoparticles on freshly cleaved mica surface. Silicon Cantilevers (OMCL, ~300kHz, 42N/m by Olympus, Japan) were used to acquire height, amplitude error, and phase images of the nanoparticles. The phase and amplitude images produced the clearest 3D visualization of the nanoparticle surface. AFM images were analyzed using the particle-analysis toolbox of the NIH ImageJ software (available at http://rsb.info.nih.gov/ij, National Institutes of Health, Bethesda, MD) to measure the area footprint (A) and volume (V) of the surface-adsorbed nanoparticles. Particle diameters < 5 nm were not included in the image analysis. Two kinds of particle diameters were calculated from the measured A and V. The ‘area-equivalent’ diameter was calculated as the diameter of a circle having the same area footprint as the nanoparticle on the imaging surface, D_A= (4A/π)^½. The ‘volume-equivalent’ diameter was calculated as the diameter of a sphere having the same volume as the nanoparticle on the imaging surface, D_V = (6V/π)^1/3. (see Supplementary information S2).

A commercial AFM instrument (Multimode/PicoForce system with NS-V controller, Bruker Nano-surface, Inc. Santa Barbara, CA) was used to image air-dried samples on freshly cleaved mica surface. A drop of peptide solution (≈ 5 μL) was allowed to stay on a mica surface for 5 min before being washed with 3 × 1 mL of milliQ water and dried in a nitrogen stream. Silicon cantilevers by Bruker (FESP, ≈ 75 kHz, 2.8 N m⁻¹) were used to acquire images of the supramolecular assemblies.