Gold Nanoparticle Modified Transparent Carbon Ultramicroelectrode Arrays for the Selective and Sensitive...

Transparent carbon ultramicroelectrode arrays (T-CUAs) were made using a previously reported facile fabrication method (Duay et al. Anal. Chem. 2015, 87, 10109). Two modifications introduced to the T-CUAs were examined for their analytical response to nitric oxide (NO^•). The first modification was the application of a cellulose acetate (CA) gas permeable membrane. Its selectivity to NO^• was extensively characterized via chronoamperometry, electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). The thickness of the CA membrane was determined to be 100 nm and 88 ± 15 nm using AFM and EIS, respectively. Furthermore, the partition and diffusion coefficients of NO^• within the CA membrane were determined to be 0.0500 and 2.44 × 10^-13 m²/s using EIS measurements. The second modification to the 1.54T-CUA was the introduction of chitosan and gold nanoparticles (CS/GNPs) to enhance its catalytic activity, sensitivity, and limit of detection (LOD) to NO^•. Square wave voltammetry was used to quantify the NO^• concentration at the CA membrane covered 1.54T-CUA with and without CS/GNPs; the LODs were determined to be 0.2 ± 0.1 and 0.44 ± 0.02 μM (S/N = 3), with sensitivities of 9 ± 9 and 1.2 ± 0.4 nA/μM, respectively. Our results indicate that this modification to the arrays results in a significant catalytic enhancement to the electrochemical oxidation of NO^•. Hence, these electrodes allow for the in situ mechanistic and kinetic characterization of electrochemical reactions with high electroanalytical sensitivity.