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streptavidin beads

Moving from Gold Particles to Magnetic Beads in IVD Assays

There are a number of reasons why a lab might want to switch from colloidal gold particles to magnetic beads (for example, streptavidin beads) in an in vitro diagnostic assay, such as swapping from optical to magnetic detection in a lateral flow format or charging the format from lateral flor to a lab automated platform. Making the shift from utilizing one nanoparticle to another, however, is not a straightforward process. There are several areas where problems may arise. There is a considerable difference, for instance, in the way gold particles and magnetic beads bind a molecule. Moreover, the methodology for applications utilizing gold particles is significantly different from that of processes that make use of magnetic beads.

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This post is about choosing the right platform for a given biomarker. If you want detailed information about this topic, download our free ebook The Advanced Guide for the use of Magnetic Beads in Chemiluminescent Immunoassays:

What is the difference between gold particles and magnetic beads?

Traditionally, gold particles bind a molecule via passive adsorption, though there are now some alternatives such as protein A/G, streptavidin or carboxylated activated particles. The particle will bind to a hydrophobic area of the protein in a non-specific way. In contrast, magnetic beads attach via a great variety of covalent bond types. As such, when switching from gold particles to magnetic beads, the nature of the molecule to be bound will have to be examined and well-understood in order to determine the best site for covalent attachment. A suitable binding site will allow for attachment to the bead while still orienting the protein in such a way that the probe site remains unobstructed.

The procedure to wash the gold particles and remove unreacted ligands is typically carried out using centrifugation. Biomagnetic separation processes, on the other hand, require a magnetic bead separator. As such, a magnetic separator will have to be acquired. Ideally, this would be a homogeneous separator in which the particles are exposed to a constant magnetic force. It is important to note that magnetic beads tend to fall out of suspension in a much higher degree than gold particles because of their higher density. As such, they must be mixed consistently and sonicated prior to use to ensure proper dispersion.

In general, magnetic separation processes are gentler, faster, more efficient, and more cost-effective than gold particle processes. Assuming that proper steps are taken to ensure a successful switch, there are numerous benefits to moving a process away from gold particles and toward magnetic particles.

Don’t forget to check these posts from our blog in order to get a deeper insight into magnetic particles and immunoassays:

Bio Sergi Gassó

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Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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