Physical adsorption, immobilization

The physical adsorption of protein onto the surface of an electrode is a simple immobilization method. The adsorption is obtained by volatilizing the buffers containing proteins. The physical adsorption needs no chemical reagent, seldom activation and rinse, so that the bioactivities of the immobilized proteins can be retained well. However, the immobilized proteins are easy to break off from the electrode, which restrict broad applications of this method. Below are some examples of the physical adsorption of proteins immobilized on electrodes. 

Immobilization strategies for electrochemical detection may involve physical adsorption, thiol-finking chemistries to gold electrodes, and organosilane finking chemistries to oxidized silicon or glass substrates. Immobilization... 

Examples of the various methods of DNA immobilization are shown in Fig. 5. Amongst these are physical adsorption and covalent immobilization. The covalent immobihzation is best exemplified by the use of organo-silane chemistries and alkanethiol chemistries. 

Fig. 5 Depictions of DNA immobilization by a covalent immobilization and b physical adsorption...

Electrochemical impedance measurements of the physical adsorption of ssDNA and dsDNA yields useful information about the kinetics and mobihty of the adsorption process. Physical adsorption of DNA is a simple and inexpensive method of immobilization. The ability to detect differences between ssDNA and dsDNA by impedance could be applicable to DNA biosensor technology. EIS measurements were made of the electrical double layer of a hanging drop mercury electrode for both ssDNA and dsDNA [34]. The impedance profiles were modeled by the Debye equivalent circuit for the adsorption and desorption of both ssDNA and dsDNA. Desorption of denatured ssDNA demonstrated greater dielectric loss than desorption of dsDNA. The greater flexibility of the ssDNA compared to dsDNA was proposed to account for this difference. 

Flowever, the focus of the major part of the chapters lies on the couphng chemistry used for DNA immobilization. Successful immobihzation techniques for DNA appear to either involve a multi-site attachment of DNA (preferentially by electrochemical and/or physical adsorption) or a single-point attachment of DNA (mainly by surface activation and covalent immobihzation or (strept)avidin-biotin linkage). Immobilization methods described here comprise physical or electrochemical adsorption, cross-linking or entrapment in polymeric films, (strept)avidin-biotin complexation, a surface activation via self-assembled monolayers using thiol linker chemistry or silanization procedures, and finally covalent coupling strategies. 

Antibodies are commonly used for the capture of target molecules on the waveguides and they are immobilized by either physical adsorption or through a self-assembly monolayer (SAM). In the former situation. 

A large number of metJiods for immobilizing biomolecules on the surface of solid substrate have been proposed in the past few decades, in which the molecules are immobilized on a carrier using covalent bonds ( i, ionic bonds (2), physical adsorption (3), cross-linkage of the biomolecules (4), or by microencapsulation (5). Immobilizing techniques are indispensable to treat biomolecules in an experiment. The provision of an immobilization process is one of the most essential processing steps that are required in order to obtain practical biomolecule carriers such as... 

Immobilization of lipases on membranes have also been described and several bioreactors were developed (see review, Balcao, Paiva Malcata, 1996). The immobilization can be done by simple physical adsorption of the lipase on hydrophobic hollow fibers or flat sheets where polypropylene types are the preferred e.g. Accnrel or Celgard) (Bouwer, Cupenus Derksen, 1997). 

Four methods have been developed for enzyme immobilization (1) physical adsorption onto an inert, insoluble, solid support such as a polymer (2) chemical covalent attachment to an insoluble polymeric support (3) encapsulation within a membranous microsphere such as a liposome and (4) entrapment within a gel matrix. The choice of immobilization method is dependent on several factors, including the enzyme used, the process to be carried out, and the reaction conditions. In this experiment, an enzyme, horseradish peroxidase (donor H202 oxidoreductase EC 1.11.1.7), will be imprisoned within a polyacrylamide gel matrix. This method of entrapment has been chosen because it is rapid, inexpensive, and allows kinetic characterization of the immobilized enzyme. Immobilized peroxidase catalyzes a reaction that has commercial potential and interest, the reductive cleavage of hydrogen peroxide, H202, by an electron donor, AH2 ... 

Initial preparative work with oxynitrilases in neutral aqueous solution [517, 518] was hampered by the fact that under these reaction conditions the enzymatic addition has to compete with a spontaneous chemical reaction which limits enantioselectivity. Major improvements in optical purity of cyanohydrins were achieved by conducting the addition under acidic conditions to suppress the uncatalyzed side reaction [519], or by switching to a water immiscible organic solvent as the reaction medium [520], preferably diisopropyl ether. For the latter case, the enzymes are readily immobilized by physical adsorption onto cellulose. A continuous process has been developed for chiral cyanohydrin synthesis using an enzyme membrane reactor [61]. Acetone cyanhydrin can replace the highly toxic hydrocyanic acid as the cyanide source [521], Inexpensive defatted almond meal has been found to be a convenient substitute for the purified (R)-oxynitrilase without sacrificing enantioselectivity [522-524], Similarly, lyophilized and powered Sorghum bicolor shoots have been successfully tested as an alternative source for the purified (S)-oxynitrilase [525],... 

After immobilizing this enzyme on the surface of insoluble matrix by physical adsorption, it was found that the Ka% value was increased to 0.08 mol/L whereas the rfl ax value stayed the same as rmax. What is the effectiveness factor of the immobilized enzyme when the substrate concentration is 1 mol/L ... 

The most successful immobilization techniques for DNA or oligonucleotides appear to be those involving multi-site attachment—either electrochemical or physical adsorption—or single-point attachment— mainly covalent immobilization or strept(avidin)/biotin linkage [26]. As an example, single-point covalent immobilization can be performed on... 

The design of an immunological-based assay involves for the most part the immobilization of an antibody on a proper solid support. The most successful immobilization techniques for antibodies appear to be those involving multisite attachment—physical adsorption—or singlepoint attachment—mainly (i) covalent immobilization (ii) protein A interaction or (iii) strept(avidin)/biotin linkage. 

As with other kinds of glycoproteins, physical adsorption is an easy way to attach the antibodies to solid surfaces, since no reagents or modification are required. These features have promoted extensive use of adsorption as immobilization methodology in immunological analysis. The adsorption has been performed on different surface, mainly... 

Their main characteristic is that the optically active reagents are immobilized over the surface of an optical component (waveguide, metallic plate, glass, prism, etc.) or in a porous matrix in a way that they are in direct contact with the analyte in the sample solution. This immobilization can be carried out by covalent bonding [29], by mechanical interactions such as physical adsorption [30], by physical entrapment or by electrostatic interactions [31]. 

Membrane bioreactors have been reviewed previously in every detail [3,4,7,8,18], There are two main types of membrane bioreactors (i) the system consists of a traditional stirred-tank reactor combined with a membrane separation unit (Figure 14.1) (ii) the membrane contains the immobilized biocatalysts such as enzymes, micro-organisms and antibodies and thus, acts as a support and a separation unit (Figure 14.2). The biocatalyst can be immobilized in or on the membrane by entrapment, gelification, physical adsorption, ionic binding, covalent binding or crosslinking [3, 7, 18]. Our attention will be primarily focused on the second case where the membrane acts as a support for biocatalyst and as a separation unit, in this study. The momentum and mass-transport process, in principle, are the same in both cases, namely when there is... 

A great deal of research has been focused on the evaluation of plasma polymers and plasma treated materials for blood and soft tissue contacting-applications (2,3). A number of studies have involved the physical adsorption or covalent attachment of a variety of biomolecules to various gas plasma-treated polymer surfaces (4,5). In such studies, however, the covalent immobilization is often assumed to take place through precursor groups formed at the biomaterial surface from ill-defined oxygen and nitrogen functionalities obtained directly from the plasma. 

The physical adsorption of gases and vapors in solids could be as well be categorized as mobile adsorption, which takes place when the adsorbed molecule acts as a gas molecule in the adsorption space, or immobile adsorption, which takes place when the adsorbed molecule is forced to vibrate around an adsorption site [2],... 

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