Fabrication of an amperometric tyramine biosensor based on immobilization of tyramine oxidase on AgNPs/l-Cys-modified Au electrode

An amperometric tyramine biosensor was constructed based on covalent immobilization of black gram tyramine oxidase onto citric acid-capped silver nanoparticles bound to surface of Au electrode through cysteine self-assembled monolayer. The enzyme electrode was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and cyclic voltametry. The biosensor showed optimum response within 8 s, when polarized at 0.25 V, pH 8.5, and 35 °C, with linearity from 0.017 to 0.25 mM and a detection limit of 0.01 mM. The biosensor was employed for measurement of tyramine in beer and sauce. The mean analytical recovery of added tyramine in beer at 0.36 and 0.72 mM were 97.2 ± 2.7 and 95.8 ± 4.1 %, respectively, and within and between batches coefficients of variation were 0.33–0.38 and 0.34–0.62 %, respectively. The enzyme electrode lost 35 % of its initial activity after its 100 uses, over a period of 2 months, when stored at 4 °C.