TABLE OF CONTENTS In many biotechnological applications, the use of a carrier fluid to transport biological objects lacks specificity: For example, it is not always possible to bring by microfluidics transport a biological target to a specific location inside the biochip. A second complementary carrier is often needed. To this extent, magnetic beads are one of the most important categories of microparticles. Between 1990 and 2002, they were developed mostly for in vitro applications, principally for biodiagnostics and biorecognition, but also for purification and separation operations. More recently, their use has reached the domain of in vivo applications, such as cancer treatment.
In this chapter, we present first the nature of magnetic beads, their magnetic characteristics, and the force that can be applied on these beads. We then give examples of trajectory calculation for applications such as separation columns and magnetic field flow fractionation (MFFF). Finally, we show how assembly of magnetic beads has been used to build new biological tools, and we focus on chains of magnetic beads, ferrofluids, and magnetic membranes.
At first sight it might seem strange to consider magnetic actuation of biological microsystems because DNA, proteins, antibodies, cells, and bacteria (except just one kind, but that is just anecdotic) [1] are not magnetic. However, the principle of functionalization has totally changed the approach: as soon as it became possible to bind DNA strands or other biological or biochemical macromolecules onto magnetic microparticles, these microparticles could be used to displace and manipulate...
