Combining novel theoretical and experimental insights into the physical electrochemistry of gold and carbon-based electrodes and baicalein flavonoid sensing

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Here, both the theoretical and experimental behavior of the flavonoid baicalein (BAI) was evaluated, considering the physical electrochemistry of carbon materials. For this purpose, experimental data based on cyclic voltammetry (CV) measurements were collected using the glassy carbon electrode (GCE) in comparison with a metallic gold electrode (GE). From a theoretical point of view, the focus was on modeling the BAI interaction with substrates through the use of graphene (its functionalizations) and a gold closed-packed slab model to understand the molecular adsorption process and verify important issues related to the analyte-substrate interaction at the atomistic level. The high-level quantum-mechanical calculations were based on density functional theory (DFT). From an analytical point of view, GCE and GE were tested for method development using differential pulse voltammetry (DPV). Regarding analytical purposes, limit of detection (LOD) values of 31.5 nmol L−1 and 68.1 nmol L−1 were estimated for GCE and GE, respectively. The standard addition method was explored with GE, while an external calibration curve approach was applied to overcome surface saturation on GCE. We found two elucidating points that may compromise electroanalysis: (i) in physisorption, the analyte adsorption occurs in parallel orientation to both substrate types, carbon- and gold-based ones, which compromises the useful electrode area; and (ii) in chemisorption, the presence of defects on the carbon-based electrode surface is responsible for a strong interaction that leads to BAI dissociation and electrode poisoning. Thus, the theoretical results support the mechanistic investigation, and novel insights into the electrochemical sensing of flavonoids are presented here.