Micelle morphology observation method of lipopeptide by negative-staining-based transmission electron microscopy

Lipopeptides, novel biosurfactants showing versatile promising applications in enhanced oil recovery, textile industry, agriculture and daily chemical products, etc., are profoundly highlighted recently. Surfactin is one of the most typical representatives of lipopetide family. The critical micelle concentration (CMC) of surfactin is as low as 10–20 mg/L. When its concentration reaches above the CMC, different micelle structure will be formed and the surface-active performances might be changed with varied micelle morphologies. Thus, observation of the changes of surfactin micellar form at different concentrations is of great significance for its new applications. But so far, the micelle structure of surfactin (and also other lipopeptide molecules) is not reported yet, and the method for effectively observing the micelle morphology is limited as well. Here, we developed a method based on transmission electron microscopy combined with negative staining to observe the morphology of surfactin micelles, with which we can clearly observe the changes of micelle morphology of surfactin (or other lipopeptides) at different concentrations. Spherical micelles only form when the concentration of surfactin is low. With the increase in concentration, rod-shaped micelles of surfactin can form. Furthermore, complex rod-shaped-micelle-layer and big ring structure will form when the concentration of surfactin is very high.