Mica Substrate Functionalization for AFM

1-(3-Aminopropyl)silatrane (APS) functionalized mica was used as the AFM substrate for all experiments. Briefly, freshly cleaved mica was incubated in 4 ml APS (167 μM) in a cuvette for 30 min and then rinsed with ddH₂O thoroughly, as described in ref. 14 (link). Ten microliters of the sample were deposited onto APS mica for 2 min, cleaned with ddH₂O, and dried with a gentle argon gas flow. Images were acquired using tapping mode in air on a MultiMode 8, Nanoscope V system (Bruker, Santa Barbara, CA) using TESPA probes (320 kHz nominal frequency and a 42 N m⁻¹ spring constant) from the same vendor.