ABSTRACT
Magnetic micro/nanoparticles with biofunctional coatings are nding increasing use in elds such as microbiology, biomedicine, and biotechnology, where they are used to label, transport, and separate biomaterials, and to deliver therapeutic drugs to a target tissue (Safarik and Safarikova 2002; Berry and Curtis 2003; Pankhurst et al. 2003; Pedro et al. 2003; Arrueboa et al. 2007; Majewski and ierry 2007). ese particles, as shown in Figure 10.1, are well suited for bioapplications for several reasons. First, they are nontoxic and are well tolerated by living organisms. Indeed, magnetic (magnetite) nanoparticles occur naturally in a diverse number of species and organisms including humans, dolphins, homing pigeons, bees, and magnetotactic bacteria (Safarik and Safarikova 2002). Second, they can be synthesized in sizes that range from a few nanometers to tens of nanometers with a narrow size distribution, which makes them ideal for probing and manipulating micro/nanoscale bioparticles and biosystems. ird, magnetic nanoparticles can be custom tailored with appropriate surface treatments to enhance biocompatibility and enable biofunctional coating with a nity biomolecules for highly speci c binding with a desired biomaterial. Fourth, magnetic nanoparticles exhibit superparamagnetic behavior, i.e., they are easily magnetized by an applied magnetic eld, but revert to an unmagnetized state once the eld is removed. us, they experience a magnetic force when subjected to a local eld gradient, and they can be used to separate or immobilize magnetically labeled biomaterials from a carrier uid using an external magnetic eld. Signi cantly, the
relatively low permeability of an aqueous carrier uid enables e cient coupling between an applied eld and magnetically labeled biomaterial. Furthermore, the low intrinsic magnetic susceptibility of most biomaterials provides substantial contrast between labeled and unlabeled material, which enables a high degree of selectivity and detection. Magnetic labeling has advantages over conventional uorescence and chemiluminescence-based biolabels. For example, small samples of magnetically labeled material can be detected using ultrasensitive ferromagnetic “spin valve” sensors, which can be integrated into micro uidic-based diagnostic systems.
