Atomic Force Microscopy Imaging of INBs

AFM was performed with a modified Bruker AXS Multimode NanoScope V at room temperature (23–25 °C). FM (Supplementary Fig. S7a) and PF (Supplementary Fig. S7b) modes were used. FM mode was used here because it achieves high force sensitivity in water and more accurately measures the surface profile of INBs and other fluid structures than other operation modes29 (link)51 (link); however, more time (10–20 min) is required to tune the imaging conditions before imaging can begin. In addition, stable operation in FM mode may not be achieved for certain tips. With PF mode, AFM can begin sooner (5–10 min) after water deposition and stable imaging can be achieved easily. However, care must be taken when interpreting topographic images acquired in PF mode29 (link). We used Si cantilevers (OMCL-AC240TS from Olympus) with a spring constant of 0.7~3.8 N/m, a nominal tip radius of ~10 nm, and a free resonance frequency of ~30 kHz in water. In FM mode, the oscillation amplitude was maintained at 1.0–1.5 nm; the set point was 13–20 Hz.