Charge and Coordination Directed Liposome Fusion onto SiO₂ and TiO₂ Nanoparticles

Abstract

TiO2 and SiO2 are very useful materials for building biointerfaces. A particularly interesting aspect is their interaction with lipid bilayers. Many past research efforts focused on phosphocholine (PC) lipids, which form supported lipid bilayers (SLB) on SiO2 at physiological conditions but are adsorbed as intact liposomes on TiO2. Low pH was required to form PC SLBs on TiO2. This work intends to understand the surface forces and chemistry responsible for such differences. Two charge neutral lipids: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 2-((2,3-bis­(oleoyloxy)­propyl)­dimethylammonio)­ethyl ethyl phosphate (DOCPe) and two negatively charged lipids: 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) and 2-((2,3-bis­(oleoyloxy)­propyl)­dimethylammonio)­ethyl hydrogen phosphate (DOCP) were used. Using calcein leakage assays, adsorption measurement, cryo-TEM, and washing, we concluded that charge is the dominating factor on SiO2. The two neutral lipids form SLB on SiO2 at pH 3 and 7, but the two negatively charged ones cannot form. On TiO2, both charge and coordination chemistry are important. The two anionic lipids formed SLB from pH 3 to 10. DOCP had stronger affinity than DOPS likely due to the tighter terminal phosphate binding of the former. The two neutral liposomes formed SLB only at pH 3, where phosphate interaction and van der Waals force are deemed important. The pH 3 prepared TiO2 DOPC SLBs are destabilized at neutral pH, indicating the reversible nature of the interaction. This work has provided new insights into two important materials interacting with common liposomes, which are important for reproducible biosensing, device fabrication, and drug delivery applications.

Human Platelet Membrane Functionalized Microchips with Plasmonic Codes for Cancer Detection

“…Furthermore, maximal signal intensity was obtained at pH 5 (Figure S5, Supporting Information). The above findings agreed with previous studies, in which acidic conditions were shown to favor the adsorption and spontaneous rupture of phospholipid vesicles to form supported lipid bilayers on silica surfaces . The protein profile of PMS was examined by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), and the obtained results confirmed the successful translocation of platelet membrane proteins to the glass substrate (Figure f) and their stability concerning multiple washing steps (Figure S6, Supporting Information).…”

Modulating Noncovalent and Covalent Forces to Control Inverse Phosphocholine Lipid Self-Assembly on Inorganic Surfaces

“…30 The distinct interaction behavior of DOCP lipid vesicles has been attributed to coordinate covalent bond formation between phosphate groups and titanol (Ti-O) groups, which enhances vesiclesurface interactions on TiO2 surfaces, whereas DOCP lipid vesicles are generally repelled from SiO2 surfaces. 32 It has also been shown that DOCP lipid vesicles can fuse with TiO2 nanoparticles across a wide range of pH conditions, reinforcing the importance of coordinate bond formation while the inability of DOCP lipid vesicles to fuse with SiO2 nanoparticles has been attributed to charge repulsion. 32 As such, existing efforts have viewed covalent and noncovalent forces as discrete factors in driving DOCP lipid vesicle interactions with TiO2 and SiO2 surfaces, respectively.…”

“…32 It has also been shown that DOCP lipid vesicles can fuse with TiO2 nanoparticles across a wide range of pH conditions, reinforcing the importance of coordinate bond formation while the inability of DOCP lipid vesicles to fuse with SiO2 nanoparticles has been attributed to charge repulsion. 32 As such, existing efforts have viewed covalent and noncovalent forces as discrete factors in driving DOCP lipid vesicle interactions with TiO2 and SiO2 surfaces, respectively. However, this mechanistic picture is likely incomplete, especially in the TiO2 case, as it is known that noncovalent forces play a universally important role in vesicle-surface adhesion processes.…”

Nanoparticles and photochemistry for native-like transmembrane protein footprinting

“…Furthermore, the coordination chemistry between TiO 2 and the phosphate group allows TiO 2 to bind reversibly with liposomes with high specificity 28 , imparting stabilizing properties not found for other NPs. For example, the interaction of TiO 2 NP with DOPC/DOCPe/DOPS liposomes via coordination is found to be more important than charge 38 . Other research showed that TiO 2 NPs stabilize a DPPC liposome even under the lengthy conditions needed to reach adsorption equilibrium of TiO 2 with the vesicles 39 .…”