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Abstract: A multicomponent enzyme sensor was used to evaluate phenolic compounds in plant-based pharmaceutical formulations. Multiwall carbon nanotubes were used as carbonaceous material used for the electrode construction. Cobalt phthalocyanine was used as electron mediator and tyrosinase as biocatalyst. The enzyme sensor performance was analyzed by cyclic voltammetry and amperometry in model solution of catechol and catechin. The cyclic voltammograms and the amperometric curves show an intense cathodic peak depending on the concentration of thephenolic compound. The cathodic peak was attributed to the reduction of enzymatically produced o-quinone at the enzyme sensor surface. For the model phenolics analyzed, the kinetics of the enzymatic reaction fitted into a Michaelis–Menten type kinetics, as confirmed by the h parameter close to 1 obtained from the Hill''s plot. The detection limits were in the range of 1.66–6.32μM demonstrating good quality performances of the enzyme sensor. Pharmaceutical samples were analyzed with multi-component biocomposite enzyme sensor to evaluate its real feasibility in pharmaceutical analysis. [Copyright &y& Elsevier]

• CuPcSO3−, PEI, HNT nanoclay and tyrosinase were used in LbL sensors and biosensors. • The use of HNT enhances the limits of detection of the sensors towards catechol. • The biosensor based on tyrosinase and HNT showed a higher reliability. Halloysite nanotubes (HNTs) are excellent candidates to improve the immobilization of electroactive materials or enzymes due to their tubular structure and properties. In this work, an improved LbL based catechol sensor has been developed using a combination of sensing materials with complementary activity. These include sulfonated copper phthalocyanine (CuPcSO3−) acting as electrocatalytic material, poly(ethyleneimine) (PEI) to increase the charge injection efficiency and the increase of the surface provided by HNTs. The LbL film has been used as the sensing platform to deposit tyrosinase in order to further enhance the performance of the developed sensor towards catechol. The LbL films were characterized by using UV–Vis, FTIR and cyclic voltammetry. The limits of detection, repeatability and reproducibility of the sensors and the biosensor were evaluated. The limits of detection were 1.23 μmol·L−1 for the optimized (PEI/CuPcSO3−) sensor, 0.987 μmol·L−1 for the (PEI/HNT/PEI/CuPcSO3−) sensor and 0.938 μmol·L−1 for the (PEI/HNT/PEI/CuPcSO3−)-Tyrosinase sensor. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this work, a multisensor system formed by nanostructured voltammetric biosensors based on phenol oxidases (tyrosinase and laccase) has been developed. The enzymes have been incorporated into a biomimetic environment provided by a Langmuir–Blodgett (LB) film of arachidic acid (AA). Lutetium bisphthalocyanine (LuPc2) has also been introduced in the films to act as electron mediator. The incorporation of the enzymes to the floating layers to form Tyr/AA/LuPc2 and Lac/AA/LuPc2 films has been confirmed by the expansion in the surface pressure isotherms and by the AFM images. The voltammetric response towards six phenolic compounds demonstrates the enhanced performance of the biosensors that resulted from a preserved activity of the tyrosinase and laccase combined with the electron transfer activity of LuPc2. Biosensors show improved detection limits in the range of 10−7–10−8 molL−1. An array formed by three sensors AA/LuPc2, Tyr/AA/LuPc2 and Lac/AA/LuPc2 has been employed to discriminate phenolic antioxidants of interest in the food industry. The Principal Component Analysis scores plot has demonstrated that the multisensor system is able to discriminate phenols according to the number of phenolic groups attached to the structure. The system has also been able to discriminate grapes of different varieties according to their phenolic content. This good performance is due to the combination of four factors: the high functionality of the enzyme obtained using a biomimetic immobilization, the signal enhancement caused by the LuPc2 mediator, the improvement in the selectivity induced by the enzymes and the complementary activity of the enzymatic sensors demonstrated in the loading plots. [Copyright &y& Elsevier]

The electron mediator properties of three subphthalocyanines (SubPcs) [hexa-chloro boron subphthalocyanine (ClSubPc), tri- tert -butyl boron subphthalocyanine ( t- BuSubPc) and hexa-phenoxy boron subphthalocyanine (PhOSubPc)] in Tyrosinase and Laccase biosensors (deposited on ITO glass) for the detection of catechol and hydroquinone were evidenced. A particularly remarkable performance was observed in the PhOSubPc-Tyr sensor, which takes account of the π-π interactions between subphthalocyanine rings and the active sites of the enzymes. Mediated electron transfer between redox enzymes and the ITO electrode improved the limits of detection by one order of magnitude, reaching 10 −7 mol·L −1 values. Studies at increasing scan rates confirmed the improvement of the charge transfer rates caused by the presence of the SubPcs. A bioelectronic tongue formed by an array of the SubPc based biosensors has been able to discriminate red wines according to their Total Polyphenol Index. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the preparation of a biomimetic Langmuir–Blodgett film of tyrosinase incorporated in a lipidic layer and the use of lutetium bisphthalocyanine as an electron mediator for the voltammetric detection of phenol derivatives, which include one monophenol (vanillic acid), two diphenols (catechol and caffeic acid) and two triphenols (gallic acid and pyrogallol). The first redox process of the voltammetric responses is associated with the reduction of the enzymatically formed o-quinone and is favoured by the lutetium bisphthalocyanine because significant signal amplification is observed, while the second is associated with the electrochemical oxidation of the antioxidant and occurs at lower potentials in the presence of an electron mediator. The biosensor shows low detection limit (1.98×10−6–27.49×10−6 M), good reproducibility, and high affinity to antioxidants (K M in the range of 62.31–144.87μM). The excellent functionality of the enzyme obtained using a biomimetic immobilisation method, the selectivity afforded by enzyme catalysis, the signal enhancement caused by the lutetium bisphthalocyanine mediator and the increased selectivity of the curves due to the occurrence of two redox processes make these sensors exceptionally suitable for the detection of phenolic compounds. [ABSTRACT FROM AUTHOR]