Magnetic nanomaterials have been extensively used for diagnostic and therapeutic applications. In biomedical realm, magnetic nanoparticles are most often used in the form of magnetic beads made by embedding magnetic nanoparticles in a suitable matrix, usually tailor-made to meet the requirements for specific applications.
The magnetic nanomaterials in a majority of biomedical and life science applications are in the form of ferrofluids, which are stable dispersions of magnetic beads in an aqueous or organic carrier medium. Nevertheless, the physical properties of the beads (such as the content of iron oxide which determine its behavior) need to be attentively designed.
Among the largest global providers of magnetic beads are Thermo Fisher Scientific, AMSBIO, IBA, Millipore, Bang Laboratories, BD Sciences, Miltenyi Biotec GmbH and other companies. In addition, many smaller firms are designing platforms specifically for cancer diagnostics by separating and enumerating circulating tumor cells.
The use of magnetic beads in molecular biology
The application of magnetic beads in molecular biology is seeing a rapid increase in both fundamental research and clinical diagnostics. For example, superparamagnetic beads are shown to be a of great use in the identification, isolation and genetic analysis of certain cells, for isolation of nucleic acids, for protein purification, as well as for the detection of bacteria and viruses.
These monosized superparamagnetic particles are known under a brand name Dynabeads, and offered by Thermo Fisher Scientific. They are produced by a method that differs from other types of magnetic particle production, which gives them favorable characteristics in molecular biology applications. They are also well suited for automated applications.
The increased use of magnetic beads in life sciences stems from the simplification they bring and the possibility to avoid centrifugation steps. The manipulation of magnetic beads in lab-on-a-chip systems is also a rapidly growing endeavor since it is possible to manipulate them at distance, without disrupting biochemical reactions.
Various applications exist for the use of DNA or RNA bound to the magnetic beads via either oligo(dT)-sequences or streptavidin attached to the surface. For example, Streptavidin Dynabeads M-280 are currently the gold standard for the isolation of biotinylated nucleic acids, antibodies or other targets due to their strong binding affinity.
A biotechnology company IBA provides MagStrep Type3 XT Beads that are coated ferri-magnetic spheres with high binding capacity and low non-specific protein binding. They are used in small scale purification schemes that have high demands for protein purity.
AMSBIO recently introduced a range of MagSi magnetic beads that contain a novel ferro fluid to join the advantages of small beads and large surface with the magnetic performance and strength of larger beads. These beads are used in a wide array of applications in genomics and proteomics.
Magnetic bead-based immunoassays and medical applications
One of the main avenues of magnetic beads application is the use of immunoassays implemented in the microfluidic format. Immunoassays are certainly indispensable in biological molecule analysis, thus they have been explored for a plethora of applications (from environmental analysis to clinical diagnostics).
When magnetic beads are used for that purpose, the detection sensitivity is increased due to the fact that many detectable molecules can be generated with merely a few immunocomplexes. Enzyme substrate is flown through the magnetic bead reaction chamber, which subsequently leads to the formation of a detectable product.
In the medical realm, the capture of pre-targeted prostate cancer cells with magnetic beads has been shown to be a viable approach. A clinically pertinent protocol for the discriminatory capture, quantification and propagation of circulating prostate tumor cells from blood by employing streptavidin-coated magnetic beads has already been developed.