Significant progress has been made in the synthesis of particles with controllable shape, structure and size. Such particles can provide diverse properties that make them potential building blocks or functionalized carriers in novel integrated systems. One of the main challenges in the development of devices that utilize micro- and nanoparticles is to provide an accurate control of particle organization on surfaces or in confined geometries. In such context self-assembly is an intriguing approach to organize large numbers of small particles efficiently.
We will first focus our attention on an example of versatile and reliable process that uses the self-assembly concept to order and immobilise particles on surfaces. This method was developed for colloidal suspensions and relies on capillary forces or convective flows as directing forces. It has been designed for accurate particle placement at arbitrary positions over large areas and is compatible with a large range of particle materials and sizes (20nm – 10µm). The process is also suitable for particle integration through micro-contact printing that allows the transfer of particles on un-patterned substrates. This approach has a broad range of applications such as the creation of resist patterns for surface patterning or the assembly of electronically and optically active nano-objects. We will show how this process can be extended to biological applications for introducing labelled beads into bioassays or patterning living cells on surfaces.
In the second part of this presentation, we will show how magnetic forces can be advantageously tuned and combined with hydrodynamic concepts to create functional assemblies of particles in microfluidic devices. We investigated several methods to create local confinement forces in microchannels to trap and manipulate magnetic microparticles. We will describe three examples of biological applications that we recently developed for i) the integration of 3D functionalized structures for protein detection or cancerous cell capture ii) the generation of a miniaturized fluidized bed for molecular preconcentration iii) the combination of droplet microfluidics and magnetic tweezers for multiplexed heterogeneous immuno-assays.