Matrix immobilisation

Wang et al.2 and Najafpour et al.3A worked with immobilised microbial cells of Nitrobacer agilis, Saccharomyces cerevisiae and Pseudomonas aeruginosa in gel beads, respectively. They found separately that the cells retained more than 90% of their activity after immobilisation by using specific oxygen uptake rate (SOUR) [mg 02g 1 (dry biomass) h 11 as the biomass activity indicator. Such differences in immobilised biomass and activity between free and immobilised biomass activities depend strongly on the particular characteristics of the microbial systems and their interaction with the support matrix. 

However, there are disadvantages to using immobilised cells. The cell may contain numerous catalytically active enzymes, which may catalyse unwanted side reactions. Also, the cell membrane itself may serve as a diffusion barrier, and may reduce productivity. The matrix may sharply reduce productivity if the microorganism is sensitive to product inhibition. One of the disadvantages of immobilised cell reactors is that the physiological state of the microorganism cannot be controlled. 

The effect of temperature on the rate of ethanol production is markedly different for free and immobilised systems. Thus while a constant increase in rate is observed with free S. cerevisiae as temperature is increased from 25 to 42 °C, a maximum occurs at 30 °C with cells immobilised in sodium alginate. The lower temperature optimum for immobilised systems may result from diffusional limitations of ethanol within the support matrix. At higher temperatures, ethanol production exceeds its rate of diffusion so that accumulation occurs within the beads. The achievement of inhibitory levels then causes the declines observed in the ethanol production rate. 

Sometimes it is impossible to effectively design out waste, and safe means have to be found to dispose of it. Many industrial processes produce relatively high levels of waste in a finely divided or dispersed form, such as ash, contaminated soil, treatment sludges, and so forth. This contaminated material is difficult to handle and process. A common approach to tackling this problem is to stabihse and sohdify the waste using a binder that immobilises contaminants within a hard matrix. This does not destroy the contaminants, but keeps them from moving into the surroimding environment. 

Immobilisation of the matrix in the SPREAD process, this takes place not at the surface of minerals, but at thiosepharose, a polymeric carbohydrate which... 

Hybridisation the matrix bonds the complementary units, one of which contains the function necessary for immobilisation. 

For trace analysis in fluids, some Raman sensors (try to) make use of the SERS effect to increase their sensitivity. While the basic sensor layout for SERS sensors is similar to non-enhanced Raman sensors, somehow the metal particles have to be added. Other than in the laboratory, where the necessary metal particles can be added as colloidal solution to the sample, for sensor applications the particles must be suitably immobilised. In most cases, this is achieved by depositing the metal particles onto the surfaces of the excitation waveguide or the interface window and covering them with a suitable protection layer. The additional layer is required as otherwise washout effects or chemical reactions between e.g. sulphur-compounds and the particles reduce the enhancement effect. Alternatively, it is also possible to disperse the metal particles in the layer material before coating and apply them in one step with the coating. Suitable protection or matrix materials for SERS substrates could be e.g. sol-gel layers or polymer coatings. In either... 

Construction of the optode for urea biosensor requires immobilisation of protein (and pH indicator) in the host matrix. There are several methods enabling protein entrapment. One can use gels, polymers, saccharose, various meshes and membranes78. 

Lofas S., Johnsson B., A novel hydrogel matrix on gold surfaces in surface plasmon resonance sensor for fast and efficient covalent immobilisation of ligands, J.Chem.Soc., Chem.Commun. 1990 21 1526-1528. 

These adsorbants are based on immobilised ligands, which have a high affinity for a particular analyte (Fig. 15.13). There are examples where antibodies have been raised to an analyte and then bound to the surface of a SPE matrix. Various types of chemistry permit this type of immobilisation and affinity chromatography is well established in biochemistry. With the proliferation with biotechnological products such as therapeutic peptides, the use of these types of columns for extraction may increase since they can be designed to be highly selective for such compounds. 

The two main immobilisation techniques on a mesoporous material are direct grafting and indirect grafting (tethering), as shown in Scheme 1. In the former case, the complex interacts directly with the matrix. In the latter case, the complex is tethered to the supporting material via a spacer ligand, which is either introduced first on the support (as shown on the upper part of Scheme 1) or integrated into the complex before being anchored onto the support (lower part of Scheme 1). 

Membranes can be used as well as a supporting material for immobilisation (e.g. polycarbonate membranes with created amino groups on the surface that allow covalent binding with glutaraldehyde). Entrapment of enzymes on electrode surfaces can be carried out with polymeric membranes such as polyacrylamide and gelatine, or by electropolymerisation of small monomers (o-phenylenediamine). Enzyme encapsulation within a sol-gel matrix has also been reported. 

Ref. Matrix Enzyme/immobilisation method Electrode configuration/ applied potential Mediator... 

Leca and Marty [26] Cider Wine Whisky Co-immobilisation of alcohol dehydrogenase (ADH), NADH oxidase and high molecular weight NAD (NAD-dextran) in a poly(vinyl alcohol) bearing stryrylpyridinium groups (PVA-SbQ) matrix Pt/+550 vs. Pt ... 

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