Ferrocenes immobilization techniques

The fourth and probably most popular enzyme immobilization technique is the entrapment technique. In this case, monomer or low molecular weight water soluble polymers are crosslinked in the presence of the enzyme to entrapment the enzyme into the polymer matrix. This has been done with a variety of redox polymer (osmium and ferrocene-based), as well as sol-gels and other hydrogels. This technique effectively covalently links the enzyme to the electrode surface and minimizes leaching and most of these polymers are hydrogels with facile transport of substrate/product in and out of the film. However, frequently this crosslinking affects specific activity of the enzyme. 

A further example of the use of this technique to introduce a ferrocene redox centre to a platinum surface is given in equation (32). A comparative survey was made of the rates of heterogeneous charge transfer between the platinum electrode and ferrocene both in solution and immobilized on the surface. Both processes show an Arrhenius temperature dependence but AGact(soIii) / A( ACT(surface bound). Absolute rate theory was unsatisfactory for the surface reaction and the need to involve electron tunnelling and a specific model for the conformation of the surface was indicated.66... 

Foulds and Lowe (1986) combined mass production of the base sensor and enzyme immobilization as follows. Using gold or platinum ink, a working and counter electrode were deposited on a ceramic substrate. After thermal treatment of the electrode material a solution containing GOD and a pyrrole derivative of ferrocene was electrochemically polymerized at the electrode. The pyrrole component forms a conducting polymer and the immobilized ferrocene acts as electron acceptor for GOD. The structured immobilization permits this technique to be used for successive enzyme fixation to multiparameter sensors. 

For the current studies the receptor P-CD was immobilized in self-assembled monolayers (SAMs) on Au(lll). P-CD is a cyclic heptamer of glucose (see Figure 1) and is well known to bind apolar guests, including ferrocene, in aqueous environment [18]. Prior to the force spectroscopy experiments SAMs of P-CD heptasulfide derivative 1 on Au(l 11) were investigated by a variety of techniques to ensure that the monolayers fulfill the requirements for a successful determination of single molecular interactions on the level of small molecules [14]. 

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