Msnl cantilever

Atomic force microscopy (AFM) images were taken with Asylum Research MFP-3D AFM (Oxford instrument, Santa Barbara, California, U.S.A.). All images of proteins immobilized on mica(0001) were acquired using an MSNL cantilever (k = 0.6 N/m, Olympus, U.S.A.) in tapping mode in air. The driving frequency of the cantilever was typically 109 kHz, the free amplitude was 0.25-0.40 V, and the damping amplitude ranged 22 to 50%. AFM images of COMP immobilized on aldehyde-terminated SAM were taken with an MSNL cantilever (k = 0.6 N/m, Olympus, U.S.A.) in buffer solution. The driving frequency was in resonance with the fundamental vibration of the cantilever, typically 37 kHz in water. All images were taken with a 0.5 x 0.5 μm² scan area. Images were acquired at speeds of 1-10 μm s⁻¹, with 1024 x 512 pixels per frame. Data acquisition were carried out using MFP-3D software developed based on Igor Pro 6.12 platform. Typically, at least 5 images were acquired for each experiment. Using tapping mode and soft cantilevers (e.g. k = 0.6 N/m) under ambient conditions, and especially in buffer media were known to exhibit little perturbation to immobilized protein molecules on surfaces.^{18 (link)–22 (link)} For imaging display and analysis, MFP-3D software were utilized, in conjunction with WSXM and ImageJ.