A voltammetric biosensor based on tyrosinase (TYR) was developed for determination of tyramine. Carbon material (multi-walled carbon nanotubes or mesoporous carbon CMK-3-type), polycationic polymer—i.e., poly(diallyldimethylammonium chloride) (PDDA), and Nafion were incorporated into titania dioxide sol (TiO2) to create an immobilization matrix. The features of the formed matrix were studied by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The analytical performance of the developed biosensor was evaluated with respect to linear range, sensitivity, limit of detection, long-term stability, repeatability, and reproducibility. The biosensor exhibited electrocatalytic activity toward tyramine oxidation within a linear range from 6 to 130 μM, high sensitivity of 486 μA mM−1 cm−2, and limit of detection of 1.5 μM. The apparent Michaelis–Menten constant was calculated to be 66.0 μM indicating a high biological affinity of the developed biosensor for tyramine. Furthermore, its usefulness in determination of tyramine in food product samples was also verified.Graphical abstractDifferent food samples were analyzed to determine tyramine using biosensor based on tyrosinaseElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-016-9612-y) contains supplementary material, which is available to authorized users.
The surface of CMK-3 carbon, synthesized by the reversible replication of mesoporous silica (SBA-15) using poly(furfuryl alcohol) as a carbon precursor, was activated by wet oxidation with an aqueous solution of HNO 3 or H 2 O 2 . The process was performed at 50°C using solution containing different concentrations of the oxidizing agent. It was found that during the modification no significant changes in textural and structural properties of CMK-3 replica occurred. However, the treatment resulted in the formation of appreciable amounts of surface species containing oxygen. XPS and DRIFT spectroscopy allowed to identify and quantify the surface functional groups. Their stability was studied by TG-FTIR measurements. CO and CO 2 were found as main gaseous products evolved during thermal decomposition under inert atmosphere. Finally, the modified samples were tested in the catalytic oxidative dehydrogenation * Corresponding author. Tel. +48 12 6632006. Fax +48 12 6340515. E-mail address: kustrows@chemia.uj.edu.pl (P. Kuśtrowski) 2 of ethylbenzene to styrene at 350°C in the presence of oxygen as an oxidizing agent (at O 2 /ethylbenzene molar ratio of 1.0 and 3.0). At the beginning of the catalytic run, the highest styrene yield and selectivity was achieved at the lower O 2 content over the catalysts treated with nitric acid. Nevertheless, all studied catalysts underwent a gradual deactivation due to coke formation and changes in the distribution of surface moieties.
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