Abstract

We propose an original approach to handle submicrometer-sized biological or inorganic materials in microfabricated devices for micro total analysis applications. Cell-sized liposomes were utilized as containers for nanoparticles, green fluorescent proteins, or DNA and handled within a microfluidic chip. Due to the micrometer size of these liposomes, their detection could be achieved by conventional optical systems. Moreover, liposomes are hardly sensitive to Brownian motion; their trapping or transportation is thereby made easy with electrostatic-based techniques, for instance, developed the past few years for cells and particles. Encapsulated materials were confined for long durations with respect to the diffusive scale time, and the liposome membrane provided excellent protection from the outside environment, inhibiting undesirable interactions. A microfluidic device consisting of a flow cell covering an array of asymmetric electrodes allowed us to convey readily liposomes by the AC electroosmosis effect. We also assessed the electrofusion of liposomes between micromachined electrodes, opening up controlled initiation of reaction inside these containers; it was exemplified by fusing differently colored liposomes. We observed that a large fraction of the liposomes fused for electric field intensity around 6 kV/cm. Applications ranging from ultrasmall biomimetic reactors to large-scale drug delivery or cell labeling can be envisaged.