Graphene-Gold Nanoparticles Nanozyme-Based Electrochemical Sensor with Enhanced Laccase-Like Activity for Determination of Phenolic Substrates

Graphene decorated with gold nanoparticles (Au-rGO) was obtained in a single-step synthesis by exfoliating graphite rods via pulses of current. The morphological and structural features of Au-rGO were explored by TEM/SEM/EDX and XRD techniques. TEM images reveal the co-existence of thin and transparent sections corresponding to few-layer graphene along with darker regions corresponding to multi-layer graphene. Such a mixture was further confirmed by XRD examination of the sample. Au-rGO was next deposited on top of a screen-printed electrode (Au-rGO/SPE), and its electro-catalytic activity toward catechol oxidation was compared with that of a laccase-modified electrode (Lac/SPE). For Au-rGO/SPE, the dependence between the peak current and catechol concentration was linear within a wide range (1.0 × 10⁻⁹–1.0 × 10⁻³ M) with a sensitivity of 0.048 A/M. The limit of quantification was very low, 1.0 × 10⁻⁹ M, and the limit of detection was calculated to be 3.3 × 10⁻¹⁰ M (S/N = 3). In contrast, the Lac/SPE has three times lower sensitivity toward catechol (0.016 A M⁻¹) and a higher LOD (3.3 × 10⁻⁶ M). The Au-rGO/SPE was tested for the detection of catechol in tap and mineral water samples with recovery percentages from 90.9% to 100.1%.