Ferrocene biosensors

Ferrioxalates, actinometry, 1225 Ferrocene biosensors diacyl peroxides, 701... 

Ferrocene biosensors continued) hydrogen peroxide, 654 hydroperoxides, 688... 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

Di Gleiia K, Hill HAO, McNeil CJ, Green MJ (1986) Homogeneous ferrocene mediated amperometiic biosensors. Anal Chem 58 1203-1205... 

A colloidal suspension of conductive vanadium pentoxide [130] can be used to perform intercalation, adsorption or encapsulation of electroactive molecules or biomolecules for electrodes or biosensor realization [131]. Encapsulation of glucose oxidase in nanocomposite films made with polyvinyl alcohol and V205 sol-gel matrix or in ferrocene intercalated V2Os sol-gel [132] were envisaged to prepare glucose biosensors. 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

The second-generation 02" biosensors are mainly based on the electron transfer of SOD shuttled by surface-confined or solution-phase mediators, as shown in Scheme 2(b). In 1995, Ohsaka et al. found that methyl viologen could efficiently shuttle the electron transfer between SOD and the glassy carbon electrode and proposed that such a protocol could be useful for developing 02 biosensors [125], Recently, Endo et al. reported an 02, biosensor based on mediated electrochemistry of SOD [148], In that case, ferrocene-carboxaldehyde was used as the mediator for the redox process of SOD. The as-developed 02 biosensor showed a high sensitivity, reproducibility, and durability. A good linearity was obtained in the range of 0 100 pM. In the flow cell system, tissue-derived 02 was measured. 

P.C. Pandey, S. Upadhyay, N.K. Shukla, and S. Sharma, Studies on the electrochemical performance of glucose biosensor based on ferrocene encapsulated ORMOSIL and glucose oxidase modified graphite paste electrode. Biosens. Bioelectron. 18,1257—1268 (2003). 

V.S. Tripathi, V.B. Kandimalla, and H.X. Ju, Amperometric biosensor for hydrogen peroxide based on ferrocene-bovine serum albumin and multiwall carbon nanotube modified ormosil composite. Biosens. Bioelectron. 21,1529-1535 (2006). 

Constantinos G. Tsiafoulis et al. report the electrochemical behaviour of a composite film based on ferrocene intercalated V205.nH20 xerogel (FeCp2-VXG) with photocrosslinkable polyvinyl alcohol with styrylpyridinium residues (PVA-SbQ), in order to be used as an electrocatalyst and host protein platform to develop an amperometric biosensor. 

Attempts to reduce interference and minimize the effect of variations in oxygen tension have resulted in the development of biosensors with improved linear ranges which operate at lower electrode potentials. They incorporate artificial electron acceptors, called mediators, to transfer electrons from the flavoenzyme (e.g. glucose oxidase) to the electrode and thus are not dependent on oxygen. Ferrocene (bis(i75-cyclopentadienyl)iron) and its derivatives are examples of redox mediators for flavoenzymes. The reaction now becomes... 

As far as the use of ferrocene molecules as amperometric sensors is concerned, they have found wide use as redox mediators in the so-called enzymatic electrodes, or biosensors. These are systems able to determine, in a simple and rapid way, the concentration of substances of clinical and physiological interest. The methodology exploits the fact that, in the presence of enzyme-catalysed reactions, the electrode currents are considerably amplified.61 Essentially it is an application of the mechanism of catalytic regeneration of the reagent following a reversible charge transfer , examined in detail in Chapter 2, Section 1.4.2.5 ... 

Gasiorowski K, Brokos JB, Szyba K, et al Evaluation of genotoxic and immunotoxic activities of potential glucose biosensor components ferrocenes. Biometals 12 19-26, 1999... 

Several variants of the biosensor in Scheme 5 have been proposed. One is a CPE containing at its tip a paste of graphite powder loaded with HRP and ferrocene ([Cp Fe(II) Cp]) mediator, which is further covered with a cellulose acetate film coated with Nafion. The biosensor is mounted on a FIA system in a three-electrode setup, as working electrode at a potential of 4-100 mV vs. SCSE and a Pt counterelectrode. The LOD (SNR 6) for H2O2 is 200 fmol (20 p,L injection of 10 nM solution), with linearity up to 25 In... 

SCHEME 9. Operation of the biosensor based on an electrode coated by a polymeric film containing immobilized HRP. The organic peroxide acts as an oxidizing agent for the ferrocene solute... 

Ferrocenyl-based polymers are established as useful materials for the modification of electrodes, as electrochemical biosensors, and as nonlinear optical systems. The redox behavior of ferrocene can be tuned by substituent effects and novel properties can result for example, permethylation of the cyclopentadienyl rings lowers the oxidation potential, and the chaige transfer salt of decamethylfer-rocene with tetracyanocthylene, [FeCpJ]" (TCNE], is a ferromagnet below = 4.8 K, and electrode surfaces modified with a pentamethylferrocene derivative have been used as sensors for cytochrome c These diverse properties have provided an added impetus to studies on ferrocene dendrimers. 

Biosensors constructed for ethanol and D-glucose measurements in beverages were built using ferrocene compounds as electron transfer mediators between the coenzyme PQQ of immobilized enzymes glucose (GDH) and alcohol (ADH) dehydrogenases and a carbon electrode surface <2003JOM(668)83>. 

Ferrocene [101-54-5] -enantiomeric separations [BIOPOLYMERS - ANALYTICAL TECHNIQUES] (V ol 4) -use m biosensors [BIOSENSORS] (Vol 4)... 

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