PEI-coated gold nanoparticles decorated with laccase: a new platform for direct electrochemistry of enzymes and biosensing applications.

This paper describes the synthesis and characterization of PEI-coated gold nanoparticles (PEI-AuNP), which were applied as a new platform in the immobilization of laccase (LAC) originating from Aspergillus oryzae. This material (PEI-AuNP-LAC) was used in the construction of a biosensor based on a glassy carbon electrode coated with a bio-nanostructured film. The occurrence of direct electron transfer (DET) between the electroactive center of LAC and the electrode surface was observed by cyclic voltammetry (CV), suggesting that the presence of AuNP in the film acts as a bridge for electron transfer. In acetate buffer solution (pH 5.0), LAC shows a pair of well-defined redox waves with a formal potential (E⁰') of 0.226V vs. Ag/AgCl (3M KCl). The biosensor response indicated a surface-controlled process with an apparent electron transfer rate constant (k(s)) of 0.4 s⁻¹, charge transfer coefficient (α) of 0.5, and surface coverage concentration (Γ) of 3.45×10⁻¹⁰ mol cm⁻². The optimized biosensor showed the following limits of detection (LOD) for the phenolic compounds tested: 0.03 μM for catechol and guaiacol; 0.14 μM for pyrogallol and 0.21 μM for hydroquinone, using square-wave voltammetry (SWV). The proposed biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (only 20% decrease in response over 90 days and after 150 measurements by SWV for each film formed). This biosensor was successfully applied to catechol quantification in spiked water samples. Furthermore, this method showed great potential for application in the development of new devices for biosensing.