Cell membranes composed of phospholipid bilayers are important components that regulate vital cellular activities such as substance transportation, signal transduction, and cell adhesion by forming the interface between the intracellular and extracellular environments. To mimic such functions of the cellular membrane, phospholipid assemblies, as represented by liposomes and micelles, have long been used as versatile biomaterials. Of them, phospholipid nanosheets, sometimes called bicelles, have recently attracted particular attention as a material motif to design a drug delivery carrier, because disk-shaped carriers tend to show longer circulation times 49 and stronger adhesion to microvascular networks 50,51 than spherical carriers. However, bicelles composed of mixtures of surfactants and phospholipids are essentially unstable and tend to undergo phase transitions and morphological changes upon alterations in the external environments. Phospholipid nanosheets that can be used for blood administration are prepared by designing surfactants incorporating self-assembling peptides. 52 Cholic acid is known to localize at the edge of the phospholipid membrane to afford phospholipid nanosheets. 53 A cholic acid derivative conjugating a metal-binding peptide sequence PHGGGPHGG (Chol-MBP; Fig. ) is designed as a surfactant. DPPC/Chol-MBP nanosheets are formed by mixing dipalmitoylphosphatidylcholine with Chol-MBP (DPPC) ([DPPC]/[Chol-MBP] = 5/1, 5.0 wt% in total). PHGGG is a naturally occurring Cu 2+ -binding motif because of the metal-coordination ability of the imidazole group of the histidine residue. 54 Since Chol-MBP can bind to two Cu 2+ ions, Chol-MBP can selfassemble at the edge of the DPPC/Chol-MBP membrane to inhibit its dissociation (Fig. ), thereby enhancing the stability of the phospholipid nanosheets against dilution.