Dielectrophoresis of functionalized lipid unilamellar vesicles (liposomes) with contrasting surface constructs

Dielectrophoresis (DEP) has been exceedingly exploited recently as an effective technique for rapid manipulation, separation, and assembly of biological particles including cells, proteins, and DNAs. However, optimizing of the DEP process with biocolloidal suspensions remains challenging, mainly due to inadequate understanding of AC polarization of complex biological structures. In this paper, we examine the DEP behavior of model functionalized lipid unilamellar vesicles (liposomes) with distinct exterior surface properties and compare the measured crossover frequency, omegac, with the theoretical prediction based on the Maxwell-Wagner interfacial polarization mechanism for a shell structure. With a uniform shell coating of calcium phosphate, we observe a drastic decrease in omegac compared to the measured value for plain liposome particles. In sharp contrast, with the patchy surface created by the adsorption of oppositely charged nanoparticles on liposome outer surfaces, we observe that omegac is independent of nanoparticle surface coverage, despite the considerable change in liposome surface conductivity by increasing adsorbed nanoparticles. Our results indicate the particle construct, rather than surface conductivity, plays a critical role in the DEP behavior of a shell particle, which is remarkably different from a solid dielectric particle.