Interfacial approach to fabricate covalently and noncovalently attached inverse-phosphocholine supported lipid bilayers on TiO₂ and SiO₂ surfaces

Inverse-phosphocholine lipids such as DOCP are intriguing biomolecules for surface functionalization because they can form supported lipid bilayers (SLBs) on titania surfaces but adsorb weakly on silica surfaces. Interestingly, these trends are nearly opposite to those of conventional phosphocholine lipids, motivating deeper investigation of how environmental parameters affect DOCP lipid vesicle adsorption phenomena. Herein, we systematically investigated how solution pH (4, 6, 8, 10) and ionic strength (50, 150, 250 mM NaCl) influence DOCP lipid vesicle adsorption behavior on titania and silica surfaces. On titania, DOCP lipid vesicles either adsorbed and ruptured to form a covalently attached SLB (acidic pH), adsorbed but did not rupture (basic pH with high salt), or did not adsorb (basic pH with low salt). Conversely, on silica, a narrow range of acidic pH, high-salt conditions triggered DOCP lipid vesicle adsorption and rupture to form a noncovalently attached SLB whereas negligible adsorption occurred in other conditions. The corresponding energetics of the vesicle-surface interaction and lipid attachment properties were analyzed and clarify how the interplay of solution pH and ionic strength modulates DOCP lipid vesicle adsorption behavior. Based on these insights, we identified suitable strategies to fabricate covalently and noncovalently stabilized inverse-phosphocholine lipid bilayers on oxide surfaces.