Keywords: real-time interaction, AFM, lipid bilayers, solubilisation, non-ionic detergents, striated domains, biomembranes, nanoscale, atomic force microscopy, detergent molecules, lipid-detergent interactions, nanotechnology
Interaction of non-ionic detergents with biomembranes at the nanoscale observed by atomic force microscopy
The interaction of two non-ionic detergents Triton X-100 (TX-100) and Tween 20 (Tw20) with lipid bilayers was studied at the nanoscale with atomic force microscopy (AFM). The real-time interaction of these two detergents with biomembranes was followed by using a mixed dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC) 1 : 1 (mol/mol) bilayer. For the two detergents, the solubilising activity was tested both below and above their critical micelle concentration (CMC) on the DOPC/DPPC bilayers. Below the CMC, Tw20 was able to solubilise the fluid DOPC leaving the gel phase unaltered on the mica while TX-100 had almost no effect on the bilayer. Above the CMC, the two detergents fully solubilised the DOPC fluid phase within the first minutes. These different behaviours were interpreted on the basis of their Hydrophile-Lipophile Balance (HLB). Another type of model membrane was also prepared to image the organisation of detergent-enriched domains at high resolution. To this end, liposomes of pre-mixed DPPC-detergent were fused on the mica substrate. It was shown that both detergents produced ordered patterns very similar to the striated domains described with helical peptides. Indeed, line-type depressions and elevated lines were observed. The depressions seemed to be provoked by the insertion of detergent molecules within the gel DPPC. This work highlights the uniqueness of AFM to evidence yet unexpected lipid-detergent interactions at the nanoscale.