Modulation of attractive colloidal interactions by lipid membrane-functionalization

Achieving simple, effective control of interactions between microparticles is an important goal of colloidal science, due both to its widespread technological relevance and its potential to illuminate the fundamental mechanisms governing structure and dynamics in complex fluids. Such control has remained elusive, however, especially with respect to attractive forces between microparticles. The studies described here adopt a biomimetic approach, functionalizing inorganic microparticles with biomolecular membranes. We provide the first reported measurements of the pair interaction energy, the key determinant of colloidal behavior, for such particles. The data demonstrate strong, tunable attractive interactions. Moreover, control of lipid composition enables a striking insight into the long-standing paradox of “like-charge attraction” observed in confined colloidal systems: G. M. Kepler and S. Fraden, Phys. Rev. Lett., 1994, 73, 356–359; D. G. Grier, J. Phys.: Condens. Matter, 2000, 12, A85–A94; M. Polin, D. G. Grier and Y. Han, Phys. Rev. E, 2007, 76, 041406–041407. Decomposing the measured interactions into charge-dependent and -independent terms, we find that the charge-dependent term in the interaction is purely repulsive, while the attraction is independent of particle charge.