Electrochemical Sensor Based on Gold Nanoparticles/Carboxylated Carbon Nanotubes for Detection of Polyphenols in Tea

To establish an analytical method for the determination of total polyphenols and catechins and rutin in tea by electrochemical sensors. The nanogold/carboxylated carbon nanotube-modified polyphenol electrochemical sensors were prepared by modifying carboxylated carbon nanotubes (SWNTs-COOH) on glassy carbon electrodes by drop coating method and then depositing nanogold (AuNPs) on their surfaces by electrodeposition, and the morphological observations and performance tests were performed by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Electrochemical characterization of gallic acid (GA), epigallocatechin gallate (EGCG), rutin and other standard substances in tea leaves as well as mixed systems simulating tea leaves was carried out with the constructed polyphenol sensors. SEM observation confirmed that the nanogold/carboxylated multi-carbon nanotubes were successfully modified on the surface of the glassy carbon electrode, and the impedance of the modified electrode was 78.2% lower than that of the bare electrode, and the peak current response value of the electrode was 253.5% of that of the bare electrode, which significantly improved the sensitivity of the modified electrode. The redox characterization of GA, EGCG and other standards revealed that the Peak I peak potentials of GA, EGCG, quercetin and epicatechin were all 0.50±0.05 V, and the corresponding peak currents Ip were linearly correlated with the concentration of substance c, which can be used as a common landmark oxidation peak for total phenol detection. While EGCG besides Peak I also has an oxidation peak Peak III with a peak potential of 0.42±0.05 V, and the rutin oxidation peak Peak I with a potential of 0.56 V. These two distinct peaks potentials can be quantified separately for EGCG and rutin along with the determination of total phenols. In the tea simulation system containing mixed polyphenols, the peak current of the sensor and the concentration of total polyphenols showed a good linear relationship in the range of 5.0×10-6~6.0×10-5 mol/L, and the correlation coefficient R2 was 0.982. The detection limit was 3.1×10-7 mol/L (S/N=3), and the recovery rate of standard addition was 96.60%~101.17%. This method is characterized with simple operation, short detection time, and no complicated sample pretreatment, which could be a new method for rapid detection of polyphenols.