Very Strong but Reversible Immobilization of Enzymes on Supports Coated with Ionic Polymers

In this chapter, the properties of tailor-made anionic exchanger resins based on films of large polyethylenimine polymers (e.g., molecular weight 25,000) as supports for strong but reversible immobilization of proteins are shown. The polymer is completely coated, via covalent immobilization, the surface of different porous supports. Proteins can interact with this polymeric bed, involving a large percentage of the protein surface in the adsorption. Different enzymes have been very strongly adsorbed on these supports, retaining enzyme activities. On the other hand, adsorption is very strong and the derivatives may be used under a wide range of pH and ionic strengths. These supports may be useful even to stabilize multimeric enzymes, by involving several enzyme subunits in the immobilization.

Immobilization of Aspergillus oryzae β-galactosidase in cation functionalized agarose matrix and its application in the synthesis of lactulose

Aspergillus oryzae β-galactosidase was immobilized in in-house quaternary ammonium agarose (QAA) and used for the first time in the synthesis of lactulose. A biocatalyst was obtained with a specific activity of 24,690 IU_H∙g^-1; protein immobilization yield of 97% and enzyme immobilization yield of 76% were obtained at 30 °C in 10 mM phosphate buffer pH 7 for standard size agarose at 100 mg_protein∙g_support^-1 which the maximum protein load of QAA. Highest yield and specific productivity of lactulose were 0.24 g∙g^-1 and 9.78 g∙g^-1 h^-1 respectively, obtained at pH 6, 100 IU_H∙g lactose^-1 enzyme/lactose ratio and 12 lactose/fructose molar ratio. In repeated-batch operation with the immobilized enzyme, the cumulative mass of lactulose per unit mass of contacted protein and cumulative specific productivity were higher than obtained with the soluble enzyme since the first batch. After enzyme activity exhaustion, the enzyme was desorbed and QAA support was reused without alteration in its maximum enzyme load capacity and without detriment in yield, productivity and selectivity in the batch synthesis of lactulose with the resulting biocatalyst. This significantly decreases the economic impact of the support, presenting itself as a distinctive advantage of immobilization by ionic interaction.

Development of a methodology for reversible chemical modification of silicon surfaces with application in nanomechanical biosensors

Hypervalent tellurium compounds have a particular reactivity towards thiol compounds which are related to their biological properties. In this work, this property was assembled to tellurium-functionalized surfaces. These compounds were used as linkers in the immobilization process of thiolated biomolecules (such as DNA) on microcantilever surfaces. The telluride derivatives acted as reversible binding agents due to their redox properties, providing the regeneration of microcantilever surfaces and allowing their reuse for further biomolecules immobilizations, recycling the functional surface. Initially, we started from the synthesis of 4-((3-((4-methoxyphenyl) tellanyl) phenyl) amino)-4-oxobutanoic acid, a new compound, which was immobilized on a silicon surface. In nanomechanical systems, the detection involved a hybridization study of thiolated DNA sequences. Fluorescence microscopy technique was used to confirm the immobilization and removal of the telluride-DNA system and provided revealing results about the potentiality of applying redox properties to chalcogen derivatives at surfaces.

Regenerative biosensor for use with biotinylated bait molecules

Label-free biosensors are ideally suited for the quantitative analysis of specific interactions among biomolecules or of biomolecules with drugs, as well as for quantitation of diagnostic markers in biofluids. In contrast to the label-dependent methods, a new assay for a particular prey molecule can be set up within few minutes by immobilizing the corresponding bait molecule on the sensor surface, using one of the common immobilization procedures. Unfortunately, the extensive application of label-free biosensors is still hampered by the fact that the immobilization of the bait molecule is usually irreversible; for that reason, a new chip (which is expensive) is required for every successful or futile attempt. Here, we present a general method for the switchable immobilization of biotinylated bait molecules on a new desthiobiotin surface, using wild-type streptavidin as a robust bridge between the chip and the biotinylated bait. The immobilization of the bait is very stable, so that many cycles of prey injection and subsequent prey removal can be carried out. For the latter, common reagents like HCl, Na₂CO₃, glycine buffer, or SDS are employed. When desired, however, streptavidin plus the biotinylated bait can be completely removed by 3min injections of biotin, guanidinium thiocyanate, pepsin, and SDS, which makes it possible to immobilize new biotinylated bait. The number of in situ regeneration cycles is unlimited during the lifetime of the chip (2-3 weeks). One chip can easily be shared by many users with unrelated tasks (as is typical in academics), or used for the fully automated screening of many different interactions (for example in pharmaceutical research). In comparison to other regenerative chips, the new chip surface has much wider applicability and all of its structural and functional parameters have been disclosed.