Free radical scavenger screening of total antioxidant capacity in herb and beverage using graphene/PEDOT: PSS-modified electrochemical sensor

• A novel sensor based on G/PEDOT:PSS/SPCE was developed for screening of TAC.
• G/PEDOT:PSS nanostructures increased surface area and conductivity of electrode.
• This system might be alternative tool for TAC evaluation in herb and herbal drinks.

This work describes the development of a novel nanocomposite- graphene/poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) modified screen-printed carbon electrode (G/PEDOT:PSS/SPCE) for the evaluation of total antioxidant capacity (TAC) based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Droplet-like nanostructures of G/PEDOT: PSS were fabricated on the SPCE surface via electrospraying. The electrochemical behaviors of both unmodified SPCE and G/PEDOT: PSS modified SPCE were investigated by cyclic voltammetry (CV) using a standard ferri/ferrocyanide [Fe(CN)6]3/4-. Interestingly, electrosprayed G/PEDOT: PSS can enhance the current response due to simple increase of the SPCE surface area. Compared to an unmodified SPCE, the peak potential difference (ΔEp) between anodic and cathodic peak potential of G/PEDOT: PSS modified SPCE substantially decreased, indicating the faster electron transfer kinetics. Moreover, our system can be used for quantitation of TAC by chronoamperometric detection of residual non-reacted DPPH level at the interference free cathodic region. With addition of standard Trolox antioxidant, the cathodic DPPH current decreased. The calibration curve of Trolox antioxidant was found in a range of 5–30 μM with a limit of detection (S/N = 3) of 0.59 μM and a limit of quantification (S/N = 10) of 1.97 μM. Finally, this novel electrochemical sensor was successfully applied for TAC evaluation in Thai herb and herbal beverage. The results showed a good agreement with the conventional UV–visible spectrophotometric results.

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