Sensitive electrochemical determination of quercetin and folic acid with cobalt nanoparticle functionalized multi-walled carbon nanotube

A nanocomposite of cobalt nanoparticle (CoNP) functionalized carbon nanotube (Co@CNT) was prepared and used to modify a glassy carbon electrode (Co@CNT/GCE). Characterization indicates the morphology of Co@CNT is CoNPs adhering on CNTs. With the nano-interface, Co@CNT provides large surface area, high catalytic activity, and efficient electron transfer, which makes Co@CNT/GCE exhibiting satisfactory electrochemical response toward quercetin (QC) and folic acid (FA). The optimum pH values for the detection of FA and QC are 7.0 and 3.0, respectively. The saturated absorption capacity (Γ*) and catalytic rate constant (k_cat) of Co@CNT/GCE for QC and FA are calculated as 1.76 × 10⁻⁹, 3.94 × 10⁻¹⁰ mol∙cm⁻² and 3.04 × 10², 0.569 × 10² M⁻¹∙s⁻¹. The linear range for both FA and QC is estimated to be 5.0 nM–10 μM, and the LODs (3σ/s) were 2.30 nM and 2.50 nM, respectively. The contents of FA and QC in real samples determined by Co@CNT/GCE are comparable with the results determined by HPLC. The recoveries were in the range 90.5 ~ 114% and the total RSD was lower than 8.67%, which further confirms the reliability of the proposed electrode for practical use.