Liposome dimensions at a glance by bright-field microscopy and fractal analysis

Patterns from evaporated micro-droplets of complex fluids represent an emerging method for biological analysis. Although the driving forces behind the interactions in droplet evaporation of liquids have been vastly explored, an analytical technique derived from this knowledge needs to be well-established. In this work, we take advantage of the knowledge of the patterns found after the evaporation of microdroplets of lipid vesicles with potassium chloride to introduce a reliable method to differentiate the micro- and nano-size of liposomes composed of zwitterionic and anionic phospholipids. We use a statistical index of complexity, fractal dimension, to correlate the liposome size with the pattern index. We conclude that the values of fractal dimensions of 1.7 ( ± 0.1) that describe a monofractal can be related to the nanoscale range of unilamellar vesicles; otherwise, the vesicle sizes range the microscale. This suggests that our method could be a practical reference to reveal the nanoscale dimension of several systems in biophysics, bioengineering, and nanotechnology.