Size distribution of particles formed in the absence (panels A-C) or presence (panels D-F) of 0.01 % (w/v) Tween 20. Particles were imaged in the frozen-hydrated state and sized at three different magnifications: 6,500×, 21,000× and 52,000×. The number of particles measured at each magnification is indicated in the respective panel. Mean particle AED values in the absence of Tween 20 were of 64.3 nm (52,000×), 96.1 nm (21,000×) and 386 nm (6,500). The mean AED values in the presence of Tween 20 were 84.3 nm (52,000×), 131 nm (21,000×) and 502 nm (6,500×).