Gold nanoclusters and nanoparticles are promising materials for applications in nanomedicine, and therefore, understanding their interaction with cell membranes is of particular importance. A series of neutral and anionic Au25(SCnH2n+1)18 monolayer protected clusters (MPCs) (briefly, Cn0 and Cn– clusters), was embedded into two types of biomimetic membranes supported by mercury electrodes. The first was a dioleoylphosphatidylcholine (DOPC) self-assembled monolayer (SAM), whereas the second was a tethered bilayer lipid membrane (tBLM) obtained by first anchoring a thiolipid monolayer to the mercury surface and then self-assembling a DOPC monolayer on top of it. The diameter of these clusters, from 1.7 to 2.7 nm depending on the thiolate ligand, is smaller than the thickness of biomembranes and biomimetic membranes. Both neutral and anionic Au25(SCnH2n+1)18 MPCs can penetrate the lipid bilayer moiety of the tBLM, without disrupting it; in particular, anionic Au25 clusters require positive transmembrane pote...