Phenols enzyme sensors

S. Cheol Chang, K. Rawson and C.J. McNeil, Disposable tyrosinase-peroxidase bi-enzyme sensor for amperometric detection of phenols, Biosens. Bioelectron., 17 (2002) 1015-1023. 

A multitude of publications describe enzyme sensors for the detection of phenolic compounds, reflecting the large variety of possible configurations. 

An enzyme sensor based on tyrosine can be used for assay of phenolic compounds at the millimole-per-liter level.103 The method is based on the following reactions ... 

Enzyme sensors for alcohols and phenols. Lower primary alcohols are oxidized by alcohol oxidase (Eq. (54))... 

In summary, the steady state and transient performance of the poly(acrylamide) hydrogel with immobilized glucose oxidase and phenol red dye (pAAm/GO/PR) demonstrates phenomena common to all polymer-based sensors and drag delivery systems. The role of the polymer in these systems is to act as a barrier to control the transport of substrates/products and this in turn controls the ultimate signal and the response time. For systems which rely upon the reaction of a substrate for example via an immobilized enzyme, the polymer controls the relative importance of the rate of substrate/analyte delivery and the rate of the reaction. In membrane systems, the thicker the polymer membrane the longer the response time due to substrate diffusion limitations as demonstrated with our pAAm/GO/PR system. However a membrane must not be so thin as to allow convective removal of the substrates before undergoing reaction, or removal of the products before detection. The steady state as well as the transient response of the pAAm/GO/ PR system was used to demonstrate these considerations with the more complicated case in which two substrates are required for the reaction. 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Various biosensors have been developed, incorporating microorganisms instead of specific enzymes. An AMD biosensor was proposed that is more sensitive to chlorophenols, especially 3- and 4-chlorophenol, than to phenol, and does not respond to their benzoates. The sensor incorporates Trichosporon beigelii (cutaneum). LOD was 2 ppb for all studied compounds, with RSD 5.5% and linearity up to 40 ppb for 4-chlorophenoP. An AMD biosensor incorporating Rhodococcus was investigated for the determination of phenol and its three monochloro derivatives. A linear relationship between the current and the concentration of these compounds was observed up to 20 p.M LOD was 4 tiM... 

The use of photosynthetic enzymes isolated from plants has been implemented in a toxicity monitor (LuminoTox, Lab Bell Inc., Shawinigan, Canada). This system can detect a range of compounds such as hydrocarbons, herbicides, phenols, polycyclic aromatic hydrocarbons (PAHs), and aromatic hydrocarbons. These enzymes have been coupled to screen-printed electrode and have been demonstrated to be able to detect triazine and phenylurea herbicides [79]. Other enzyme inhibitions have been used to detect biotoxins from plant, animals, bacterial, algae, and fungal species (e.g., ricin, botulinum toxins, mycotoxins, cyanobacterial toxins). However, since the identity and specificity of the above toxic compound can be very important during the analysis, other sensor systems such as immunosensors may be preferred to give a better indication to toxin type and identity than the use of enzyme inhibition tests. 

Electropolymerization of phenols proceeds similarly to that for pyrrole poly(phenol) itself is probably a mixture of para- and meta-linked units. Films are generally continuous and free from such defects as pinholes. They have been used for corrosion protection, as permselective films, " and as pH sensors. Like poly(pyrrole) films, electropolymerized phenol films have a number of features that make them attractive for immobilizing an enzyme. First these films can be grown under electrochemical control from aqueous buffered solution at neutral pH. Second a wide variety of phenol derivatives are available that allow some control over the films physical characteristics. Third these films are permselective, which could be useful in preventing interfering species from reaching the... 

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