A biosensor based on laccase immobilized on nitrogen-doped multiwalled carbon nanotubes and graphene oxide for polyphenol detection.

The use of nanomaterials allows the design of ultrasensitive biosensors with advantages in the detection of organic molecules. Catechol and catechin are molecules that occur naturally in fruits, and their presence in products like dyes and wines affects quality standards. In this study, catechol and catechin were measured at the nanoscale by means of cyclic voltammetry. The oxidation of laccase immobilized on nitrogen-doped multiwalled carbon nanotubes (Lac/CN -MWCNT) and on graphene oxide (Lac/GO) was used to measure the concentrations of catechol and catechin. Nitrogen-doped multiwalled carbon nanotubes (CN -MWCNT) were synthesized by spray pyrolysis and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). Covalently bonded hybrids with laccase (Lac/CN -MWCNT and Lac/GO) were generated. Catalytic activity of free enzymes determined with syringaldazine yielded 14 584 UmL. With Lac/CN -MWCNT at concentrations of 6.4 mmol L activity was 9326 U mL, while enzyme activity measured with Lac/GO at concentration of 6.4 mmol L was 9 234 U mL. The Lac/CN -MWCNT hybrid showed higher stability than Lac/GO at different ethyl alcohol concentrations. The Lac/CN -MWCNT hybrid can measure concentrations, not previously reported, as low as 1 × 10 mol L by measuring the electric current responses.