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The polystyrene beads formed by this mechanism may have an average diameter of around 200 μm. The beads are then permeated with a "blowing agent", a material that enables the beads to be expanded. Pentane is commonly used as the blowing agent.
Ion-exchange resin beads. An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange, that is also known as an ionex. [1] It is an insoluble matrix (or support structure) normally in the form of small (0.25–1.43 mm radius) microbeads, usually white or yellowish, fabricated from an organic polymer substrate.
Bind – Microbeads bind to the desired target, relative to the specific affinity of the ligand on the surface of the beads. Wash – Microbeads will move to the side of the tube in response to a magnetic field, along with the bound material. This happens quickly and efficiently because of the magnetic field and the micro-sized particles.
Dynabeads were developed after John Ugelstad managed to create uniform polystyrene spherical beads (defined as microbeads) of exactly the same size, [1] [2] at the University of Trondheim, Norway in 1976, something otherwise only achieved by NASA [3] in the weightless conditions of SkyLab. Dynabeads are typically 1 to 5 micrometers in diameter.
Pre-expanded beads of polystyrene are injected into a preheated aluminum mold at low pressure. Steam is then applied to the polystyrene which causes it to expand more to fill the die. The final pattern is approximately 97.5% air and 2.5% polystyrene.
From the other hand, metallic beads are not the appropriate tool for optical tweezers experiments. Polystyrene beads scatter light weaker than metallic (in order to get the same intensity as getting from 40 nm gold bead, the polystyrene bead should be ~125 nm! [3]), but it has the advantage that it can be combined with optical tweezers experiments.