Background The deficiency of vitamin B2 can lead to many health problems. Therefore, it is necessary to develop a sensitive, selective and fast method for the determination of vitamin B2 in food samples. In this work, a sensitive, selective and low-cost electrochemical sensor was developed using poly (glutamic acid) and Zinc oxide nanoparticles (ZnO NPs) for vitamin B2 in non-alcoholic beverage and milk samples. Methods The modification of the electrode surface was carried out by electropolymerization of glutamic acid on ZnO NPs–carbon paste electrode (ZnO NPS–CPE). The prepared electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-Ray diffraction (XRD). CV and square wave voltammetry (SWV) were used to investigate the electrochemical behavior of vitamin B2 at the modified electrode. The effect of various parameters such as amount of ZnO NPs, polymerization cycle, concentration of the monomer, pH, scan rate and accumulation time were optimized to obtain maximum sensitivity at the modified electrode. Results The developed sensor showed high electrocatalytic activity towards vitamin B2. Under the optimized conditions, the developed sensor showed a linear response in the range 0.005–10 µM with a low detection limit of (LOD) 0.0007 ± 0.00001 µM and high sensitivity of 21.53 µA/µM. Conclusions A reproducible, repeatable, stable and selective sensor was successfully applied for the quantification of vitamin B2 in beverage and milk samples with acceptable recoveries in the range of 88–101%.

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An efficient sensor was developed for the simultaneous determination of gallic and folic acid in juice samples using an electrochemically pretreated carbon paste electrode. The electrode was characterized by CV and EIS. The electrochemical behavior of GA and FA was evaluated by CV and SWV. The electrode exhibited high electrocatalytic activity towards GA and FA due to high surface area. Under the optimized condition, linear plots in the ranges of 0.08–13 μM and 0.1 to 15 μM were obtained for GA and FA, respectively. The proposed method was successful for the simultaneous determination of GA and FA in juice samples with satisfactory recovery.

A simple, low-cost, and stable electrochemical sensor for vanillin is reported based on a glassy carbon electrode (GCE) modified with poly (phenylalanine) and electrochemically reduced graphene oxide (ERGO) composite (poly (phenylalanine)/ERGO/GCE). The surface structure of the bare and modified electrodes was characterized by Fourier transform infrared and scanning electron microscopy. The electrochemical behavior of vanillin at phenylalanine)/ERGO/GCE) was also studied by CV. Poly (phenylalanine)/ERGO/GCE) exhibited high electrocatalytic activity for the electrochemical oxidation of vanillin due to the synergetic effects of poly (phenylalanine) and ERGO. From linear sweep voltammetry study, the electrode reaction of vanillin is adsorption-controlled process. Furthermore, several electrochemical parameters such as number of electrons transferred (n=2), number of protons transferred (H+ = 2), electron transfer coefficient (α = 0.66) and surface concentration of vanillin (Ґ = 0.32 nmol cm−2) were calculated. SWV was used for quantitative determination of vanillin at phenylalanine)/ERGO/GCE). Under optimum conditions, the oxidation peak current of vanillin increased linearly with its concentration in the range 0.25–120 µM with a low detection limit of 0.025 µM. The developed sensor was successfully applied for the determination of vanillin in food and soft drink samples.

A simple and low-cost electrochemical sensor based on poly(phenylalanine) and function­nalized multi-walled carbon nanotubes (F-MWCNTs) modified glassy carbon electrode (GCE) was developed for the determination of vitamin B6 (VB6). The surface morphology of modified glassy carbon electrodes was investigated with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrocatalytic activities of the bare and modified electrodes were investigated in the presence of ferri-ferrocyanide redox couple using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The exchange current density (jo = 2462 µA cm-2) and electron transfer rate constant (ko = 0.002 cm s−1) were calculated using 5 mM K3[Fe(CN)6]. The electro­chemical activity of poly(phenylalanine)/F-MWCNT/GCE towards VB6 oxidation was investigated using CV. Parameters including the number of electrons transferred (n = 2), number of protons transferred (H+ = 2), electron transfer coefficient (α = 0.51) and surface concentration of VB6 (G = 0.24 nmol cm−2) were calculated. At the optimal experimental conditions, the oxidation peak current of VB6 measured by square wave voltammetry (SWV) was found proportional to its concentration in two linear ranges of 0.5 to 20 µM and 20 to 200 µM with a low detection limit (LOD) of 0.038 µM and limit of quantification (LOQ) of 0.125 µM. Finally, the sensor was successfully used to determine VB6 in soft drink and pharmaceutical formulation samples.