Immobilized affinity adsorbents

Mathematical Modeling of Bioproduct Adsorption Using Immobilized Affinity Adsorbents... 

The use of small affinity adsorbent particles immobilized in hydrogel beads has been investigated for whole broth processing (1). The adsorbent particles can contain biospecific ligands covalently attached to a porous solid support. A mathematical model was developed to study bioproduct adsorption using immobilized affinity adsorbent beads in batch operation. 

Figure 1 shows a schematic diagram of an immobilized affinity adsorbent bead. Hydrogel, by virtue of its extremely high water content (>90%), offers limited diffusional resistance to the desired product. It is therefore used as an inert matrix to support... 

Figure 1. Schematic diagram of an immobilized affinity adsorbent bead.

In the past, similar bidispersed systems have been investigated and modeled in the catalyst deactivation area (5-7). However, modeling of immobilized affinity adsorbent beads is more complex due to the non-linearity introduced by the rapid ligand binding reaction which is dependent on the product concentration. 

Technologies for immobilizing proteins on surfaces that have been developed over the last 25 years are particularly critical to the continued development of biosensors. There a dozens of techniques for activating surfaces so as to be able to covalently bond proteins while maintaining their biological activity. These methods have been used routinely for manufacturing adsorbents for affinity chromatography, dip-stick type analytical methods, e.g., immunoassays, and immobilized enzymes for commercial catalysts. 

Physically adsorbed species are immobile in groundwater but may be remobilized if replaced by other species with a stronger affinity to the solid surface. 

Species held on a surface by ion exchange (such as calcium ions on clay) are also immobile in groundwater. As with physically adsorbed species, they may be replaced by ions with a greater affinity to the solid surface. 

Since many metallic catalysts have high adsorption affinities, we often find that certain poison molecules are adsorbed in an immobile form after only a very few collisions with the catalyst surface. In this situation, the outer periphery of the catalyst particle will be completely poisoned while the inner shell will be completely free of poison. The thickness of the poisoned shell grows with prolonged exposure to poison molecules until the pellet is completely deactivated. During the poisoning process, the boundary between active and deactivated regions is relatively sharp. 

At present, a wide range of solid substrates are available for protein immobilization. According to the protein attachment strategies, namely, adsorption, affinity binding, and covalent binding, all these substrates can be separated into three main parts. Surfaces like ploy(vinylidene fluoride) (PVDF), poly(dimethylsiloxane) (PDMS), nitrocellulose, polystyrene, and poly-1-lysine coated glass can adsorb proteins by electrostatic or hydrophobic forces. A potential drawback of such substrates is the difficulty... 

Immobilized antibodies may be used as affinity adsorbents for the antigens that stimulated their production (Figure 6.15). Antibodies, like many other biomolecules, may be immobilized on a suitable support matrix by a variety of chemical coupling procedures. 

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