Next Article in Journal
Numerical Simulation Analysis of a Capacitive Pressure Sensor for Wearable Medical Devices
Previous Article in Journal
Experimental Study of Temperature Effects on the Dynamic Response of Medium- and Low-Speed Maglev Trains
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Proceeding Paper

Electropolymerized Dyes as Sensing Layer for Natural Phenolic Antioxidants of Essential Oils †

by
Alena Kalmykova
*,
Anastasiya Zhupanova
and
Guzel Ziyatdinova
Analytical Chemistry Department, Kazan Federal University, Kremleyevskaya, 18, 420008 Kazan, Russia
*
Author to whom correspondence should be addressed.
Presented at The 11th International Electronic Conference on Sensors and Applications (ECSA-11), 26–28 November 2024; Available online: https://sciforum.net/event/ecsa-11.
Eng. Proc. 2024, 82(1), 18; https://doi.org/10.3390/ecsa-11-20480
Published: 26 November 2024

Abstract

Essential oils are widely used in aromatherapy, food, and pharmaceutical industries. They contain a range of electroactive natural phenolic antioxidants like eugenol, trans-anethole, thymol, carvacrol, and vanillin. Therefore, the sensitive voltammetric determination of these compounds is of practical interest. Voltammetric sensors based on the layer-by-layer combination of carbon nanotubes and electropolymerized dyes were developed. Pyrogallol red, mixture of phenol red and p-coumaric acid, thymolphthalein, bromocresol purple were used as monomers. The created sensors were used in the quantification of target analytes using differential pulse voltammetry in a Britton–Robinson buffer. The detection limits in the range of 3.7 × 10−8–7.3 × 10−7 M were achieved.

1. Introduction

Essential oils have a wide application in aromatherapy as a part of alternative medicine, as well as in the food, pharmaceutical, and cosmetic industry as fragrance and flavor additives [1,2,3]. The antibacterial, antimicrobial, antiviral, and antioxidant properties of essential oils are caused by the presence of bioactive compounds including natural phenolic antioxidants such as eugenol, trans-anethole, thymol, carvacrol, vanillin, etc. [4]. The noticeable prooxidant effect is typical for low-molecular antioxidants such as phenolic compounds when presented in high concentration [5]. Thus, quantification of these marker compounds in essential oils is of practical necessity. The presence of electroactive fragments in the phenolic antioxidants structure makes it possible to use voltammetry for their determination. However, the number of voltammetric sensors for the determination of individual antioxidants in essential oils is quite limited [6,7,8,9,10,11,12,13,14]. Almost all of them are based on the application of electrode surface modifiers, among which the polymeric coverages are out of consideration.
Recently, the effectivity of electropolymerized triphenylmethane dyes as a sensing layer for antioxidants including phenolic compounds has been shown [15,16,17,18,19,20,21]. Thus, the current work deals with the development of novel voltammetric sensors for the quantification of natural phenolic antioxidants of essential oils using electropolymerized dyes as a sensing layer. Triphenylmethane dyes (pyrogallol red, thymolphthalein, bromocresol purple, and phenol red) have been used as monomers and p-coumaric acid as a co-monomer. Layer-by-layer combinations with carbon nanomaterials (single- (SWCNTs) or multi-walled nanotubes (MWCNTs)) have been applied to provide sufficient electroconductivity of the electrodes. The surface and electron transfer parameters of the developed sensors have been characterized by scanning electron microscopy (SEM), voltammetry, and electrochemical impedance spectroscopy.

2. Materials and Methods

Thymol (99.5% purity) from Sigma (Steinheim, Germany), 98% carvacrol, 99% vanillin, and 99% eugenol from Aldrich (Steinheim, Germany), 98% trans-anethole from TCI (Tokyo, Japan) were used as standards. Their 1.0 × 10−2 M stock solutions were prepared in ethanol (rectificate) or methanol (c.p.) and stored at +4 °C. Thymolphthalein (95% purity) and 98% p-coumaric acid from Sigma (Steinheim, Germany), phenol red from Sigma-Aldrich (St. Louis, MO, USA), pyrogallol red, and 90% bromocresol purple from Sigma-Aldrich (Steinheim, Germany) were used as monomers. Their 1.0 × 10−2 M (1.0 × 10−3 M for pyrogallol red) stock solutions were prepared in ethanol (methanol for thymolphthalein). The exact dilution was used for the preparation of less concentrated solutions.
Other reagents were of c.p. grade and were used as they were.
MWCNTs (outer Ø 40–60 nm, inner Ø 5–10 nm, l = 0.5–500 µm), carboxylated MWCNTs (inner Ø 9.5 nm, l = 1.5 µm, carboxylation degree > 8%), and polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes (SWCNTs-f) (Ø 1.1 nm, l = 0.5–1.0 nm) from Aldrich (Steinheim, Germany) were used as a platform for further polymeric coating immobilization. Homogeneous suspensions of MWCNTs (0.5 mg mL−1 in 1% sodium dodecylsulfate (Panreac, Barcelona, Spain)), carboxylated MWCNTs (1.0 mg mL−1 in 1% sodium dodecylsulfate), and SWCNTs-f (1.0 mg mL−1 in dimethylformamide) were prepared by sonication for 30 (for MWCNTs and SWCNTs-f) or 15 (for carboxylated MWCNTs) min in an ultrasonic bath (WiseClean WUC-A03H (DAIHAN Scientific Co., Ltd., Wonju-si, Republic of Korea).
Bare GCE were mechanically polished on the alumina slurry (0.05 μm grain), thoroughly rinsed with acetone and distilled water. Then, 2 μL of carbon nanomaterial suspension was drop casted and evaporated to dryness for 7 (for MWCNTs) or 10 min.
Electropolymerization under conditions of cyclic voltammetry was used for the formation of the polymeric coverage. The working conditions of the process were found for each monomer individually depending on the voltammetric response of the target analyte.
Potentiostats/galvanostats Autolab PGSTAT 302N with the FRA 32M module (Metrohm B.V., Utrecht, The Netherlands) and µAutolab Type III (Eco Chemie B.V., Utrecht, The Netherlands) with NOVA 1.10.1.9 and Nova 1.7.8 software, respectively, were used for the electrochemical measurements. GCE (3 mm diameter) from CH Instruments, Inc. (Bee Cave, TX, USA) or from BASi® Inc. (West Lafayette, IN, USA) and modified electrodes, a reference Ag/AgCl electrode, and auxiliary electrode (platinum wire) were placed in the electrochemical glass cell containing supporting electrolyte and cyclic or differential pulse voltammograms were recorded.
The pH measurements were carried out using the “Expert-001” pH meter (Econix-Expert Ltd., Moscow, Russia) with a glassy electrode.
A MerlinTM high-resolution field emission scanning electron microscope (Carl Zeiss, Oberkochen, Germany) operated at 5 kV accelerating voltage and a 300 pA emission current was applied for the electrode surface morphology characterization.

3. Results and Discussion

3.1. Polymer-Based Sensors Fabrication and Charcaterization

All dyes under study and p-coumaric acid (Figure 1) contain phenolic fragments in their structure and are electrochemically active at the GCE modified with carbon nanomaterials. Taking into account that electron detachment proceeds easier from the phenolate ion, the basic medium could be preferable for electropolymerization. However, the partial oxidation of monomers by air oxygen occurs under basic conditions. Therefore, dyes’ electropolymerization was performed at neutral pH.
There are well-defined oxidation peaks on the cyclic voltammograms (Figure 2, curve 1) which are shifted a bit in the anodic direction on the following scans. The oxidation currents are significantly decreased with the growth of scans number indicating formation of non-conductive coverages.
Electropolymerization conditions (supporting electrolyte, monomer concentration, number of scans, potential range, and scan rate) providing the best voltammetric response of the target analyte were found (Table 1). The following analytes were tested: thymol, vanillin, eugenol, and trans-anethole at the poly(thymolphthalein)-, poly(bromocresol purple)-, poly(pyrogallol red)-, and poly(phenol red–co–p-coumaric acid)-modified electrodes, respectively.
The surface morphology of the electrodes was checked by SEM (Figure 3). The successful immobilization of the coverages at the modified electrodes was clearly seen vs. bare GCE (Figure 3a).
The electrochemical properties of the polymer-modified electrodes were studied using ferro/ferricyanide ions in 0.1 V KCl. The electroactive surface was significantly increased compared to bare GCE (88 ± 5 mm2 for poly(thymolphthalein)/MWCNTs/GCE, 42 ± 1 mm2 for poly(bromocresol purple)/SWCNTs-f/GCE, 96 ± 2 mm2 for poly(pyrogallol red)/Carboxylated MWCNTs/GCE, and 11.4 ± 0.6 mm2 for poly(phenol red–co–p-coumaric acid)/MWCNTs/GCE vs. 8.9 ± 0.3 mm2 for bare GCE). The heterogeneous electron transfer rate constant calculated from the electrochemical impedance spectroscopy data is in the range from 4.14 × 10−5 to 9.12 × 10−5 cm s−1 which confirms the improvement of the electron transfer at the polymer-modified electrodes.

3.2. Sensing of Phenolic Antioxidants

The created electrodes were applied for sensing of natural phenolic antioxidants—marker of essential oils (thymol, vanillin, eugenol, and trans-anethole).
The effect of Britton–Robinson buffer pH on voltammetric response parameters was tested for each antioxidant. The highest oxidation currents were observed at pH 2.0 for all studied analytes that agreed well with reported earlier data [5]. The increase in pH leads to slow decease in the oxidation peak current of the antioxidants due to the chemical oxidation with air oxygen.
Under differential pulse voltammetry conditions, the linear response of the sensors toward target phenolic antioxidants was obtained in a wide range of concentrations. The corresponding analytical characteristics are presented in Table 2. The analytical characteristics of the sensors are comparable or improved vs. existing ones [6,7,8,9,10,11,12,13,14].
Sensing of natural phenolic antioxidants of essential oils was highly accurate as proved by recovery values (98–102%). The main advantage of the developed sensors is the high selectivity of response in the presence of typical interfering substances and other natural phenolic antioxidants (Table 3).

4. Conclusions

Electropolymerized thriphenylmethane dyes have been shown to be an effective sensing layer for the potential application in electroanalysis of major phenolic antioxidants-markers of essential oils. The sensing system is easy to fabricate, highly reproducible, and provides a sensitive, selective, and reliable response to target analytes. Future development of the topic under study to be focused on the application of the sensors in real samples analysis for their standardization and quality control. Furthermore, the fabrication of screen-printed electrodes as a basis for sensing layer immobilization can significantly simplify the measurements, reduce its cost, and make it more attractive for use in practice.

Author Contributions

Conceptualization, G.Z.; methodology, A.K., A.Z. and G.Z.; validation, A.K., A.Z. and G.Z.; investigation, A.K. and A.Z.; writing—original draft preparation, A.K. and G.Z.; writing—review and editing, G.Z.; visualization, A.K., A.Z. and G.Z.; supervision, G.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

The authors thank Aleksei Rogov (Laboratory of Scanning Electron Microscopy, Interdisciplinary Center for Analytical Microscopy, Kazan Federal University) for the SEM measurements.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Ali, B.; Al-Wabel, N.A.; Shams, S.; Ahamad, A.; Khan, S.A.; Anwar, F. Essential oils used in aromatherapy: A systemic review. Asian Pac. J. Trop. Biomed. 2015, 5, 601–611. [Google Scholar] [CrossRef]
  2. Ni, Z.-J.; Wang, X.; Shen, Y.; Thakur, K.; Han, J.; Zhang, J.-G.; Hu, F.; Wei, Z.-J. Recent updates on the chemistry, bioactivities, mode of action, and industrial applications of plant essential oils. Trends Food Sci. Technol. 2021, 110, 78–89. [Google Scholar] [CrossRef]
  3. Guzmán, E.; Lucia, A. Essential Oils and Their Individual Components in Cosmetic Products. Cosmetics 2021, 8, 114. [Google Scholar] [CrossRef]
  4. Zuzarte, M.; Salgueiro, L. Essential oils chemistry. In Bioactive Essential Oils and Cancer; de Sousa, D.P., Ed.; Springer: Cham, Switzerland, 2015; pp. 19–61. [Google Scholar] [CrossRef]
  5. Ziyatdinova, G.K.; Budnikov, H.C. Natural phenolic antioxidants in bioanalytical chemistry: State of the art and prospects of development. Russ. Chem. Rev. 2015, 84, 194–224. [Google Scholar] [CrossRef]
  6. Bertuola, M.; Fagali, N.; de Mele, M.F.L. Detection of carvacrol in essential oils by electrochemical polymerization. Heliyon 2020, 6, e03714. [Google Scholar] [CrossRef] [PubMed]
  7. Robledo, S.N.; Pierini, G.D.; Nieto, C.H.D.; Fernández, H.; Zon, M.A. Development of an electrochemical method to determine phenolic monoterpenes in essential oils. Talanta 2019, 196, 362–369. [Google Scholar] [CrossRef] [PubMed]
  8. Song, B. Electrochemical sensing of monoterpene phenols in plant essential oils using a molecularly imprinted polymer dual-template sensor. Int. J. Electrochem. Sci. 2023, 18, 100381. [Google Scholar] [CrossRef]
  9. Pierini, G.D.; Bortolato, S.A.; Robledo, S.N.; Alcaraz, M.R.; Fernández, H.; Goicoechea, H.C.; Zon, M.A. Second-order electrochemical data generation to quantify carvacrol in oregano essential oils. Food Chem. 2022, 368, 130840. [Google Scholar] [CrossRef]
  10. Ziyatdinova, G.; Ziganshina, E.; Budnikov, H. Voltammetric sensing and quantification of eugenol using nonionic surfactant self-organized media. Anal. Methods 2013, 5, 4750–4756. [Google Scholar] [CrossRef]
  11. Ziyatdinova, G.; Ziganshina, E.; Romashkina, S.; Budnikov, H. Highly sensitive amperometric sensor for eugenol quantification based on CeO2 nanoparticles and surfactants. Electroanalysis 2017, 29, 1197–1204. [Google Scholar] [CrossRef]
  12. Maciel, J.V.; Silva, T.A.; Dias, D.; Fatibello-Filho, O. Electroanalytical determination of eugenol in clove oil by voltammetry of immobilized microdroplets. J. Solid State Electrochem. 2018, 22, 2277–2285. [Google Scholar] [CrossRef]
  13. Kowalcze, M.; Wyrwa, J.; Dziubaniuk, M.; Jakubowska, M. Voltammetric determination of anethole on La2O3/CPE and BDDE. J. Anal. Methods Chem. 2018, 2018, 2158407. [Google Scholar] [CrossRef]
  14. Ziyatdinova, G.K.; Antonova, T.S.; Mubarakova, L.R.; Budnikov, H.C. An amperometric sensor based on tin dioxide and cetylpyridinium bromide nanoparticles for the determination of vanillin. J. Anal. Chem. 2018, 73, 801–808. [Google Scholar] [CrossRef]
  15. Zhang, R.; Liu, S.; Wang, L.; Yang, G. Electroanalysis of ascorbic acid using poly(bromocresol purple) film modified glassy carbon electrode. Measurement 2013, 46, 1089–1093. [Google Scholar] [CrossRef]
  16. Banu, R.; Swamy, B.E.K. Poly (Bromocresol purple) incorporated pencil graphite electrode for concurrent determination of serotonin and levodopa in presence of L-Tryptophan: A voltammetric study. Inorg. Chem. Commun. 2022, 141, 109495. [Google Scholar] [CrossRef]
  17. Ziyatdinova, G.; Guss, E.; Morozova, E.; Budnikov, H.; Davletshin, R.; Vorobev, V.; Osin, Y. Simultaneous voltammetric determination of gallic and ellagic acids in cognac and brandy using electrode modified with functionalized SWNT and poly(pyrocatechol violet). Food Anal. Methods 2019, 12, 2250–2261. [Google Scholar] [CrossRef]
  18. Taei, M.; Hasanpour, F.; Tavakkoli, N.; Bahrameian, M. Electrochemical characterization of poly(fuchsine acid) modified glassy carbon electrode and its application for simultaneous determination of ascorbic acid, epinephrine and uric acid. J. Mol. Liq. 2015, 211, 353–362. [Google Scholar] [CrossRef]
  19. Promsuwan, K.; Kaewjunlakan, C.; Saichanapan, J.; Soleh, A.; Saisahas, K.; Thipwimonmas, Y.; Kongkaew, S.; Kanatharana, P.; Thavarungkul, P.; Limbut, W. Poly(phenol red) hierarchical micro-structure interface enhanced electrode kinetics for adsorption and determination of hydroquinone. Electrochim. Acta 2021, 377, 138072. [Google Scholar] [CrossRef]
  20. Zhupanova, A.; Guss, E.; Ziyatdinova, G.; Budnikov, H. Simultaneous voltammetric determination of flavanones using an electrode based on functionalized single-walled carbon nanotubes and polyaluminon. Anal. Lett. 2020, 53, 2170–2189. [Google Scholar] [CrossRef]
  21. Guss, E.V.; Ziyatdinova, G.K.; Zhupanova, A.S.; Budnikov, H.C. Voltammetric determination of quercetin and rutin in their simultaneous presence on an electrode modified with polythymolphthalein. J. Anal. Chem. 2020, 75, 526–535. [Google Scholar] [CrossRef]
Figure 1. Structure of monomers under study.
Figure 1. Structure of monomers under study.
Engproc 82 00018 g001
Figure 2. Electropolymerization of triphenylmethane dyes: (a) 1.0 × 10−5 M thymolphthalein at the MWCNTs/GCE in phosphate buffer pH 7.0; (b) 2.5 × 10−5 M bromocresol purple at the SWCNTs-f/GCE in phosphate buffer pH 7.0; (c) 1.0 × 10−4 M pyrogallol red at the carboxylated MWCNTs/GCE in Britton–Robinson buffer pH 7.0; (d) 1.0 × 10−4 M mixture of phenol red and p-coumaric acid at the MWCNTs/GCE in Britton–Robinson buffer pH 7.0.
Figure 2. Electropolymerization of triphenylmethane dyes: (a) 1.0 × 10−5 M thymolphthalein at the MWCNTs/GCE in phosphate buffer pH 7.0; (b) 2.5 × 10−5 M bromocresol purple at the SWCNTs-f/GCE in phosphate buffer pH 7.0; (c) 1.0 × 10−4 M pyrogallol red at the carboxylated MWCNTs/GCE in Britton–Robinson buffer pH 7.0; (d) 1.0 × 10−4 M mixture of phenol red and p-coumaric acid at the MWCNTs/GCE in Britton–Robinson buffer pH 7.0.
Engproc 82 00018 g002
Figure 3. SEM images of the sensor surface: (a) bare GCE; (b) poly(thymolphthalein)/MWCNTs/GCE; (c) poly(bromocresol purple)/SWCNTs-f/GCE; (d) poly(pyrogallol red)/Carboxylated MWCNTs/GCE; (e) poly(phenol red–co–p-coumaric acid)/MWCNTs/GCE.
Figure 3. SEM images of the sensor surface: (a) bare GCE; (b) poly(thymolphthalein)/MWCNTs/GCE; (c) poly(bromocresol purple)/SWCNTs-f/GCE; (d) poly(pyrogallol red)/Carboxylated MWCNTs/GCE; (e) poly(phenol red–co–p-coumaric acid)/MWCNTs/GCE.
Engproc 82 00018 g003
Table 1. Electropolymerization conditions of triphenylmethane dyes (n = 5; p = 0.95).
Table 1. Electropolymerization conditions of triphenylmethane dyes (n = 5; p = 0.95).
Sensing Layerc, MNumber of ScansPotential Range, Vυ,
mV s−1
Supporting
Electrolyte
Poly(thymolphthalein)/MWCNTs1.0 × 10−5100.0–1.01000.1 M phosphate buffer pH 7.0
Poly(bromocresol purple)/SWCNTs-f2.5 × 10−5100.0–1.2100
Poly(pyrogallol red)/Carboxylated MWCNTs1.0 × 10−4100.0–1.375Britton–Robinson buffer pH 7.0
Poly(phenol red–co–p-coumaric acid)/MWCNTs1.0 × 10−4150.0–1.250
Table 2. Figures of merit for voltammetric sensors for natural phenolic antioxidants of essential oils.
Table 2. Figures of merit for voltammetric sensors for natural phenolic antioxidants of essential oils.
SensorAnalyteMethodEox, VLinear Dynamic Range, MDetection Limit, M
Poly(thymolphthalein)/MWCNTs/GCEThymolDPV 10.815.0 × 10−8–2.5 × 10−5
2.5 × 10−5–1.0 × 10−4
3.7 × 10−8
Carvacrol0.831.0 × 10−7–1.0 × 10−5
1.0 × 10−5–1.0 × 10−4
6.3 × 10−8
Poly(bromocresol purple)/SWCNTs-f/GCEVanillinDPV0.861.0 × 10−7–5.0 × 10−6
5.0 × 10−6–2.5 × 10−5
6.4 × 10−8
Poly(pyrogallol red)/Carboxylated MWCNTs/GCEEugenolDPV0.577.5 × 10−7–1.0 × 10−47.3 × 10−7
Poly(phenol red–co–p-coumaric acid)/MWCNTs/GCEtrans-AnetholeAdDPV 20.951.0 × 10−7–7.5 × 10−6
7.5 × 10−6–7.5 × 10−5
9.5 × 10−8
1 Differential pulse voltammetry, 2 Adsorptive differential pulse voltammetry.
Table 3. Tolerance limits of interferences for the determination of natural phenolic antioxidants of essential oils using poly(triphenylmethane dye)-modified electrodes.
Table 3. Tolerance limits of interferences for the determination of natural phenolic antioxidants of essential oils using poly(triphenylmethane dye)-modified electrodes.
InterferenceTolerance Limit, M
1.0 × 10−6 M
Thymol or Carvacrol
1.0 × 10−6 M
Vanillin
5.0 × 10−6 M
Eugenol
1.0 × 10−6 M
trans-Anethole
K+, Mg2+, Ca2+, NO3, Cl, SO42−1.0 × 10−31.0 × 10−35.0 × 10−31.0 × 10−3
Glucose, rhamnose, sucrose1.0 × 10−41.0 × 10−45.0 × 10−41.0 × 10−4
Thymol02.5 × 10−52.5 × 10−7
Cavacrol05.0 × 10−52.5 × 10−7
Vanillin05.0 × 10−40
trans-Anethole1.0 × 10−705.0 × 10−4
Eugenol5.0 × 10−61.0 × 10−41.5 × 10−5
α-Pinene1.0 × 10−45.0 × 10−55.0 × 10−42.5 × 10−7
Limonene1.0 × 10−45.0 × 10−55.0 × 10−45.0 × 10−7
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Kalmykova, A.; Zhupanova, A.; Ziyatdinova, G. Electropolymerized Dyes as Sensing Layer for Natural Phenolic Antioxidants of Essential Oils. Eng. Proc. 2024, 82, 18. https://doi.org/10.3390/ecsa-11-20480

AMA Style

Kalmykova A, Zhupanova A, Ziyatdinova G. Electropolymerized Dyes as Sensing Layer for Natural Phenolic Antioxidants of Essential Oils. Engineering Proceedings. 2024; 82(1):18. https://doi.org/10.3390/ecsa-11-20480

Chicago/Turabian Style

Kalmykova, Alena, Anastasiya Zhupanova, and Guzel Ziyatdinova. 2024. "Electropolymerized Dyes as Sensing Layer for Natural Phenolic Antioxidants of Essential Oils" Engineering Proceedings 82, no. 1: 18. https://doi.org/10.3390/ecsa-11-20480

APA Style

Kalmykova, A., Zhupanova, A., & Ziyatdinova, G. (2024). Electropolymerized Dyes as Sensing Layer for Natural Phenolic Antioxidants of Essential Oils. Engineering Proceedings, 82(1), 18. https://doi.org/10.3390/ecsa-11-20480

Article Metrics

Back to TopTop