Silicon nitride scanasyst air probe

The morphology of the A-L liposomes was examined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). For TEM analysis, 10 μL of the liposomal formulation was uniformly loaded on a carbon-coated copper grid for 1 min, after which the films were negatively stained with 10 μL of 1% phosphotungstic acid solution for 1 min. Excess sample and stain were blotted with filter paper, and the copper grid was dried for imaging using a HITACHI H-7500 transmission electron microscope (Hitachi, Tokyo, Japan) at 50,000× magnification. To acquire AFM topographic images, the A-L sample solution was dropped on to the surface of mica and dried under nitrogen gas for 2 h. The samples were observed with a Bioscope Resolve atomic force microscope (Bruker Nano Surfaces, Santa Barbara, CA, USA) in PeakForce quantitative nanomechanical imaging mode. The A-L suspension was imaged with a scan rate of 1 Hz. A Bruker silicon-nitride ScanAsyst Air probe with a spring constant of 0.4 N/m was used. All images were processed with the NanoScope Analysis software (Nanoscope Analysis, Bruker-AXS, Santa Barbara, CA, USA) and the Young’s modulus of A-L was calculated by fitting the retract curve using the Derjaguin–Muller–Toropov model.31