Advantages of Immobilisation

Biosensors require highly active enzymes/biomolecules therefore, the immobilisation methods must be chosen in such a way that they can achieve a high sensitivity and functional stability. This is important for economic reasons also. The measurable activity gives an idea about the biocatalytic efficiency of an immobilised enzyme. The rate of substrate conversion should rise linearly with enzyme concentration. The measured reaction rates depend not only on the substrate concentration and the kinetic constants (Michaelis Menten constant) and (maximum velocity of the reaction) but also on the immobilisation effects. The following effects have been observed [157] due to the immobilisation process  

A decrease in the affinity of the enzyme to the substrate (increase in due to conformational changes of the enzyme on immobilisation. 

It has been predicted [159] that, in the future, the immobilisation techniques compatible with microelectronic mass production processes will be utilised for the fabrication of amperometric enzyme electrodes. 

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Immobilised cells have all the advantages of immobilised enzymes. Cell immobilisation is preferred for reactions catalysed by intracellular enzymes because it avoids tedious and expensive extraction and purification procedures, which often result in preparations of low yield and stab ty. 

Another case of heterogeneous systems refers to immobilized enzymes. The kinetic behaviour of a bound enzyme can differ significantly from that of the same enzyme in free solution. The properties of an enzyme can be modified by suitable choice of the immobilisation protocol, whereas the same method may have appreciably different effects on different enzymes. These changes may be due to conformational alterations within the enzyme, immobilisation procedure, the presence and nature of the immobilisation support. The advantages of immobilised enzymes are for instance in reusability and possibility to use continuous mode. 

The introduction of immobilised enzymes has several advantages over the chemical de-acylation of fl-lactam. List as many as you can. (You may need to refer back to Figures 6.13-6.16 and the associated text... 

Several L-amino acids are produced on a large scale by enzymatic resolution of N-acetyl-D,L-amino adds (Figure A8.4). Acylase immobilised on DEAE-Sephadex is for example employed in a continuous process while Degussa uses the free acylase retained in a membrane reactor. In the latter process the advantage of reuse of the enzyme and homogeneous catalysis are combined. 

Perhaps the most effective demonstration of the advantages of evanescent wave interrogation is provided by the optical biosensor platform depicted in Figure 5. The platform consists of a multimode slab waveguide on the upper surface of which antibodies have been immobilised. 

Use of immobilised chelating agents for sequestering trace metals from aqueous and saline media presents several significant advantages over chelation-solvent extraction approaches to this problem [193,194], With little sample manipulation, large preconcentration factors can generally be realised in relatively short times with low analytical blanks. 

Acetylcholinesterase was immobilised by entrapment into a PVA-SbQ matrix (see experimental details in Refs. [88,95]). The need of polymer hydration slightly increases the response times, when compared to other immobilisation techniques. Nevertheless, the entrapment presents the advantage of providing biosensors with longer lifetimes due to the protective effect of the polymer matrix. 

In comparison to traditional biphasic catalysis using water, fluorous phases or polar organic solvents, catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications the use of a defined transition metal complex immobilised on a liquid ionic support has already shown its unique potential. 

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