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. 2021 Nov 17;21(22):7639.
doi: 10.3390/s21227639.

Cerium(IV) and Iron(III) Oxides Nanoparticles Based Voltammetric Sensor for the Sensitive and Selective Determination of Lipoic Acid

Guzel Ziyatdinova  1 , Liliya Gimadutdinova  1
Affiliations

Cerium(IV) and Iron(III) Oxides Nanoparticles Based Voltammetric Sensor for the Sensitive and Selective Determination of Lipoic Acid

Guzel Ziyatdinova et al. Sensors (Basel). .

Abstract

A novel voltammetric sensor based on CeO2·Fe2O3 nanoparticles (NPs) has been developed for the determination of lipoic acid, playing an essential role in aerobic metabolism in the living organism. Sensor surface modification provides a 5.6-fold increase of the lipoic acid oxidation currents and a 20 mV anodic shift of the oxidation potential. The best voltammetric parameters have been obtained for the 0.5 mg mL-1 dispersion of CeO2·Fe2O3 NPs. Scanning electron microscopy (SEM) confirms the presence of spherical NPs of 25-60 nm, and their aggregates evenly distributed on the electrode surface and formed porous coverage. This leads to the 4.4-fold increase of the effective surface area vs. bare glassy carbon electrode (GCE). The sensor shows a significantly higher electron transfer rate. Electrooxidation of lipoic acid on CeO2·Fe2O3 NPs modified GCE is an irreversible diffusion-controlled pH-independent process occurring with the participation of two electrons. The sensor gives a linear response to lipoic acid in the ranges of 0.075-7.5 and 7.5-100 μM with the detection limit of 0.053 μM. The sensor is selective towards lipoic acid in the presence of inorganic ions, ascorbic acid, saccharides, and other S-containing compounds. The sensor developed has been tested on the pharmaceutical dosage forms of lipoic acid.

Keywords: amperometric sensors; electrooxidation; lipoic acid; metal oxide nanoparticles; pharmaceutical analysis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Cyclic voltammograms of 5.0 µM lipoic acid (curve 2) at the bare GCE (a) and CeO2·Fe2O3 NPs/GCE (b) in PB pH 7.0 (curve 1). Potential scan rate is 100 mV s−1. CeO2·Fe2O3 = 0.5 mg mL−1.
Figure 2
Figure 2
Effect of CeO2·Fe2O3 NPs concentration on the oxidation potential (a) and currents (b) of 5.0 µM lipoic acid in PB pH 7.0.
Figure 3
Figure 3
Surface morphology of bare GCE (a) and CeO2·Fe2O3 NPs/GCE (b) obtained by SEM.
Figure 4
Figure 4
(a) Cyclic voltammograms of 1.0 mM [Fe(CN)6]4− at the bare GCE (curve 2) and CeO2·Fe2O3 NPs/GCE (curve 3) in 0.1 M KCl (curve 1). (b) Chronoamperograms of 1.0 (curve 1) and 2.0 mM (curve 2) [Fe(CN)6]4− at bare GCE. Insert is the plot of I vs. t −1/2 obtained from chronoamperometric measurements.
Figure 5
Figure 5
(a) Nyquist plots (dots are experimental data, lines are fitted spectra) for the bare GCE (1) and CeO2·Fe2O3 NPs/GCE (2). Redox probe is 1.0 mM [Fe(CN)6]4−/3−. The supporting electrolyte is 0.1 M KCl. E = 0.23 V, the frequency range is 10 kHz–0.04 Hz, and amplitude is 5 mV. (b) Randles equivalent circuits used for the impedance spectra fitting for the bare GCE (1) and CeO2·Fe2O3 NPs/GCE (2). Rs—active electrolyte resistance, Rct—charge transfer resistance, Q—constant phase element, and W—Warburg impedance.
Figure 6
Figure 6
(a) Lipoic acid (3.8 µM) oxidation potential and currents at various pH of supporting electrolyte. (b) Cyclic voltammograms of 10 µM lipoic acid at CeO2·Fe2O3 NPs/GCE in PB pH 7.0 at various potential scan rates.
Scheme 1
Scheme 1
Electrooxidation of lipoic acid.
Figure 7
Figure 7
Effect of pulse parameters on the oxidation potentials (a) and oxidation currents (b) of 5.0 µM lipoic acid in PB pH 7.0.
Figure 8
Figure 8
Differential pulse voltammetric response of the sensor towards various concentrations of lipoic acid in PB pH 7.0.
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