4- Aminophenol-sensor

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

The polymer resulting from oxidation of 3,5-dimethyl aniline with palladium was also studied by transmission electron microscopy (Mallick et al. 2005). As it turned out, the polymer was formed in nanofibers. During oxidative polymerization, palladium ions were reduced and formed palladium metal. The generated metal was uniformly dispersed between the polymer nanofibers as nanoparticles of 2 mm size. So, Mallick et al. (2005) achieved a polymer- metal intimate composite material. This work should be juxtaposed to an observation by Newman and Blanchard (2006) that reaction between 4-aminophenol and hydrogen tetrachloroaurate leads to polyaniline (bearing hydroxyl groups) and metallic gold as nanoparticles. Such metal nanoparticles can well be of importance in the field of sensors, catalysis, and electronics with improved performance. 

In potentiometric sensors, an electrical potential between the working electrode and a reference electrode is measured at zero current conditions in a solution containing ions that exchange with the surface. The first potentiometric MIP sensor was prepared in 1992 by Vinokurov (1992). The substrate-selective polyaniline electrode was electrosynthesized with polypyrrole, polyaniline, and aniline-p-aminophenol copolymers. The development of an MIP-based potentiometric sensor was reported in 1995 by Hutchins and Bachas (1995). This potentiometric sensor has high selectivity for nitrite with a low detection limit of (2 + l)x 10 M (Fig. 15.10). 

In general, EC reactions are typically observed according to the following general rank order (by relative ease of oxidation) o,p-quinol and o,p-aminophenol > tertiary amine > m-quinol rv phenol rv arylamine > secondary amine thiol > thioether primary amines, aliphatic alcohols. (HDVs) each redox active metabolite are obtained from the response across adjacent EC-Array sensors. These data are a reflection of the kinetic and thermodynamic components of electron transfer reactions. Since chemical structure is a critical determinant of an analyte s redox behavior, the intrinsic generation of an HDV with EC-Array provides qualitative information for each species. 

Two immunosensors developed by O Regan et al. [89,90] have demonstrated their usefulness for the early assessment of acute myocardial infarction (AMI). Human heart fatty-acid binding protein (H-FABP) is a biochemical marker for the early assessment of AMI. The authors constructed an amperometric immunosensor for the rapid detection of H-FABP in whole blood. The sensor is based on a one-step, direct sandwich assay in which the analyte and an alkaline phosphatase (AP) labelled antibody are simultaneously added to the immobilized primary antibody, using two distinct monoclonal mouse anti-human H-FABP antibodies. The substrate p-amino-phenyl phosphate is converted to p-aminophenol by AP, and the current generated by its subsequent oxidation at +300 mV vs. Ag/AgCl is measured. The total assay time is 50 min, and the standard curve was linear between 4 and 250 ng ml . The intra- and inter-assay coefficients of variation were below 9%. No cross-reactivity of the antibodies was found with other early cardiac markers, and endogenous substances in whole blood did not have an... 

A review appeared on piezoelectric quartz crystals used as detectors for phenols in air, after coating with Triton X-100 and 4-aminoantipyrine (78), or with activated carbon cloth impregnated with various compounds, such as poly(vinyl pyrrolidone). A piezoelectric sensor was proposed for determination of trace amounts of phenol and alkylphenols in air. The problems attaining selectivity of the adsoption membranes and operating conditions were addressed . An AT-cut quartz crystal, coated with a hydrophobic PVC layer and operating in the thickness shear mode, has been used to detect 4-aminophenol, after conversion to a hydrophobic indophenol dye and adsorption on the polymer layer. The mode of preparation of the PVC coating affects the sensitivity of the detector , a... 

Peng, H. Yin, F. Zhou, A.H. Yao, S.Z. Characterization of electrosynthesized poly (o-aminophenol) as a molecular imprinting material for sensor preparation by means of quartz crystal impedance analysis. Anal. Lett. 2002, 35, 435-450. 

Owing to the broad spectrum of substrates for both enzymes, the sensor responds to various catecholamines, aminophenols and ferrocene derivatives. The best sensitivities were obtained for aminophenol and epinephrine where the lower limit of detection is 100 pM. The recycling sensor was used to trace the secretion of catecholamines in cultures of adrenal chromaffin cells. Furthermore both a sandwich assay for IgG and displacement of enzyme labeled cocaine have been indicated by the amplification enzyme sensor. 

Advanced process state estimation, prediction, and control via hybrid process modeling, 144-154 Aminophenols, use as sensor for subnanomolar concentrations, 70-80 Analyte concentrations, measurement using fluorescent lifetime, 99-108... 

The main difference between the two types of sensors is that the first type (based on phenol oxidases or peroxidase) uses a low applied potential (-100 - 0 mV vs. Ag/AgCl) (3), whereas the second type (based on CDH or GDH) needs a higher potential (300 - 400 mV V5. Ag/AgCl) (9,11,13) to be able to oxidize the phenols and therefore the risk of electrooxidizing interfering compounds in the sample is higher. Tyrosinase, laccase and peroxidase can all be used for both phenolic and diphenolic compounds, however, for laccase and tyrosinase the sensitivity is much higher for catecholic compounds (3). CDH and GDH require a quinone, therefore a diphenol or aminophenol is needed. 

Some of the mentioned electrodes contain poly(pyrol) [55,57], poly(aniline) [56,58] and its derivatives poly(a-naphtylamine) [59], poly(o-phenylenediamine and poly(o-aminophenol) [60]. In the electrode [55], the conductive polymer layer was immobilized on platinum or glassy carbon. The polymer membrane sensitive to oxytetracycline hydrochloride contained various anti-ions of tetraphenylborate phosphotungstate and silicotungstate. Optimum properties were reached by the Pt/PPy/PVC (OTC-TPB) sensor containing tetraphenyl borate. It shows the Nernstial response in the concentration range of 4.0 x 10 to 5.0 x 10 mol L", very low detection limit of 1.0 x 10" mol L" (0.03 ppm) and response time < 25 s. The developed sensor was applied in pharmaceutical analysis. 

J.P. Li, J. Zhao and X.R Wei, A sensitive and selective sensor for dopamine determination based on a molecularly imprinted electropolymer of o-aminophenol. Sens. Actuat B-Chem 140 (2) 663-669, 2009. 

Electrodes modified by eiectrodeposited 3-methylPT can be used as chemical sensors for organic and especially biological interesting molecules. The modified surfaces catalyze the oxidation of several compounds (e.g. ferrocyanide, catechol, ascorbic acid, hydroquinone, dopamine, epinephrine, acetaminophene, p-aminophenol, and reduced nicotinamide adenine dinucleotide). The sensitivity of these polymer-coated electrodes is 4 to 10 times higher than pure electrodes of platinum. Binary and also ternary mixtures can also be analyzed these electrodes are also suitable as an amperometric detector for flow injection analysis [211, 212]. 

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