An amperometric biosensor based on laccase immobilized onto Fe₃O₄NPs/cMWCNT/PANI/Au electrode for determination of phenolic content in tea leaves extract.

A method is described for the construction of an amperometric biosensor for detection of phenolic compounds based on covalent immobilization of laccase onto iron oxide nanoparticles (Fe₃O₄NPs) decorated carboxylated multiwalled carbon nanotubes (cMWCNTs)/polyaniline (PANI) composite electrodeposited onto a gold (Au) electrode. The modified electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 3s at pH 6.0 (0.1 M sodium acetate buffer) and 35°C, when operated at 0.3 V vs. Ag/AgCl. Linear range, detection limit were 0.1-10 μM (lower concentration range) and 10-500 μM (higher concentration range), and 0.03 μM respectively. The sensor measured total phenolic content in tea leaves extract. The enzyme electrode lost 25% of its initial activity after its 150 uses over a period of 4 months, when stored at 4°C.