After 1h of self-assembly, sample aliquots (~20 μL) were deposited on top of a copper grid for 30 s. Next, water was drawn from the sample and the grid was placed for 30 s in contact onto a drop of 2% aqueous potassium phosphotungstate at pH 7.2. Finally, the grid was dried first at room temperature, and then in vacuo. Image analysis was performed using ImageJ software.