We demonstrate the optical manipulation of cells and dielectric particles on the surface of silicon nitride waveguides. Glass particles with 2microm diameter are propelled at velocities of 15microm/s with a guided power of 20mW. This is approximately 20 times more efficient than previously reported, and permits to use this device on low refractive index objects such as cells. Red blood cells and yeast cells can be trapped on the waveguide and pushed along it by the action of optical forces. This kind of system can easily be combined with various integrated optical structures and opens the way to the development of new microsystems for cell sorting applications.
We present a new family of microfluidic chips hot embossed from a commercial fluorinated thermoplastic polymer (Dyneon THV). This material shares most of the properties of fluoro polymers (very low surface energy and resistance to chemicals), but is easier to process due to its relatively low melting point. Finally, as an elastic material it also allows easy world to chip connections. Fluoropolymer films can be imprinted by hot embossing from PDMS molds prepared by soft lithography. Chips are then sealed by an original technique (termed Monolithic-Adhesive-Bonding), using two different grades of fluoropolymer to obtain uniform mechanical, chemical and surface properties. This fabrication process is well adapted to rapid prototyping, but it also has potential for low cost industrial production, since it does not require any curing or etching step. We prepared microfluidic devices with micrometre resolution features, that are optically transparent, and that provide good resistance to pressure (up to 50 kPa). We demonstrated the transport of water droplets in fluorinated oil, and fluorescence detection of DNA within the droplets. No measurable interaction of the droplets with the channels wall was observed, alleviating the need for surface treatment previously necessary for droplet applications in microfluidic chips. These chips can also handle harsh organic solvents. For instance, we demonstrated the formation of chloroform droplets in fluorinated oil, expanding the potential for on chip microchemistry.
In this work, the effect of humidity and water intercalation on the friction and wear behavior of few-layers of graphene and graphene oxide (GO) was studied using friction force microscopy. Thickness measurements demonstrated significant water intercalation within GO affecting its surface topography (roughness and protrusions), whereas negligible water intercalation of graphene was observed. It was found that water intercalation in GO contributed to wearing of layers at a relative humidity as low as ∼30%. The influence of surface wettability and water adsorption was also studied by comparing the sliding behavior of SiO/GO, SiO/Graphene, and SiO/SiO interfaces. Friction for the SiO/GO interface increased with relative humidity due to water intercalation and condensation of water. In contrast, it was observed that adsorption of water molecules lubricated the SiOSiO interface due to easy shearing of water on the hydrophobic surface, particularly once the adsorbed water layers had transitioned from "ice-like water" to "liquid-like water" structures. Lastly, an opposite friction trend was observed for the graphene/SiO interface with water molecules failing to lubricate the interface as compared to the dry graphene/SiO contact.
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