The main reason for changing from latex to magnetic latex particles is the need for a change from an homogeneous to an heterogeneous immunoassay. Latex beads are micrometer sized polystyrene beads. They are made of polymer chains that form a sphere with a hydrophobic exterior that can participate in hydrophobic interaction. The beads bind proteins through passive adsorption or can be functionalized with chemical groups which better bind amine groups on proteins to bind them. Magnetic latex particles have an easy protocol that allows you to do washing steps quickly and efficiently, which helps to improve analytical sensitivity and to reduce interference from sample components. The main consideration in shifting from a process that utilizes latex beads to one that uses magnetic latex beads will be the physical separation process itself. Applications that utilize latex beads traditionally make use of a centrifuge or, alternatively, tangential filtration. In contrast, processes that use magnetic latex beads are carried out in a biomagnetic separator. As such, it is necessary to acquire an adequate separator for the process. Ideally, this would be a homogeneous separator.
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Practical concerns of magnetic beads
Practical concerns when working with magnetic beads include being aware that they have a stronger tendency than latex particles to fall out of solution because of their higher density. Thus, when using magnetic beads, it is important that the suspension undergoes constant mixing. Typically, this is done by placing the bead suspension on a mixer to insure that the beads remain evenly dispersed. Differently to latex particles, a ready to use magnetic bead suspension needs to be resuspended prior to use.
The chemistry of attachment to the particle is not an issue when switching from latex to magnetic latex beads, as it would be when switching over from gold nanoparticles. Both latex and magnetic latex beads use the same types of covalent bonds to attach molecules, so there is no need to seek out alternate attachment sites on the protein. A better quality in the covalent binding can be achieved with magnetic particles because of their faster separation or washing steps.
The main issue when making a switch from latex particles to magnetic latex particles is the difference in the techniques that utilize the two types of particles. Once the protocols are in place, magnetic separation processes prove to be faster and more efficient than protocols that utilize non-magnetic latex particles.
Example of Latex beads in Research
Latex beads are used to study phagocytosis. Latex beads are fluorescently labeled so you can track them as they are phagocytosed by phagocytes. The beads are also used in techniques such as magnetic or optical tweezers. Other experiments have tested viscosity of a membrane or cytoskeletal interactions. Latex beads are also used in agglutination studies. For example, an antigen can be passively adsorbed onto a latex bead, then put in the presence of a sample. If the sample contains IgM antibodies against that antigen, the beads will agglutinate (cluster) because IgM forms a pentamer that will bind multiple antigen on multiple beads.