Highly-sensitive electrochemical sensing platforms for food colourants based on the property-tuning of porous carbon

Recent advances in electrochemical sensors based on nanomaterials for detection of red dyes in food products: A review

Red dyes as Allura Red (E129), Amaranth (E124), Ponceau 4R (E123), Erythrosine (E127) and Carmoisine (E122), are very popular food additives due to their stability, low cost, and minimal microbial contamination. Despite these advantages, their consumption may result in asthma, hyperactivity, carcinogenic effects, etc depending on the uptake and age. Therefore, the United States Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) have managed the permissions of allowed daily intake (ADI) for consumption levels of these dyes to be 0.01-7.0 mg/kg to assure foodstuffs consumer's safety and avoid their adverse effects. Yet, many countries as Japan and USA have prohibited their use in food and drinks to reduce their possible health risks. Based on the above concentration ranges, highly sensitive and selective detection techniques are required, accordingly, the application of electrochemical sensors for the analysis of these dyes in food samples is very promising due to their superior sensitivity and selectivity, low cost and rapid response compared to traditional spectrophotometric or chromatographic methods. Also, they can be miniaturized, portable and require no complicated sampling or preparation procedures, besides being ecofriendly which allows their commercialization for public consumers in fast detection kits. In this review, the role of nanomaterials such as: carbon-based, transition metal oxides, metal organic frameworks, ionic liquids and others in enhancing the detection properties of modified electrochemical sensors for red dyes will be evaluated in terms of the type of nanomaterial applied, tested food samples and their impact on the evaluation of foodstuffs quality.

Combination of colorimetry, inner filter effect-induced fluorometry and smartphone‑based digital image analysis: A versatile and reliable strategy for multi-mode visualization of food dyes

Herein, a multi-mode visualization platform was initiated for in-situ detection of food dyes (FDs) by combining colorimetry, fluorometry and smartphone‑based digital image analysis, in which water-dispersible quantum dots (QDs) were served as nanoprobes. Colorimetry was achieved by color comparison, while both fluorometry and fluorescence quantification were performed through inner filter effect (IFE)-induced fluorescence quenching, then color information (RGB & gray-scale values) of colorimetry and fluorometry was picked by a smartphone to reconstruct digitized alignments. Since IFE mechanism was concentration-dependent but did not rely on the interaction between fluorophore and quencher, the whole process of fluorescence response could be finished within 10 s, and both color gradients and fluorescence changes showed fine mappings to FDs concentrations in the range of 1.0 × 10^-3∼0.035 mg/mL for brilliant blue, and 1.0 × 10^-4∼0.1 mg/mL for Allura red and sunset yellow. As a proof-of-concept, the in-situ multi-mode visualization of these FDs in real beverages was experimentally proved to be highly feasible and reliable as compared with instrumental techniques like UV-vis/fluorescence spectrometry, along with HPLC. Finally, this strategy was extended to the multi-mode visualization of non-food dyes in three simulated wastewater samples with high credibility by contrast with the true additive amounts of model dyes.

Carbon Paper Modified with Functionalized Poly(diallyldimethylammonium chloride) Graphene and Gold Phytonanoparticles as a Promising Sensing Material: Characterization and Electroanalysis of Ponceau 4R in Food Samples

This paper presents a novel eco-friendly sensing material based on carbon paper (CP) volumetrically modified with a composite nanomodifier that includes functionalized poly(diallyldimethylammonium chloride) graphene (PDDA-G) and phytosynthesized gold nanoparticles (phyto-AuNPs). The functionalization of graphene was justified by Fourier-transform infrared spectroscopy. The phyto-AuNPs (d = 6 nm) were prepared by "green" synthesis with the use of strawberry leaf extract. The sensing material was characterized using scanning electron microscopy, electrochemical impedance spectroscopy, and voltammetry. The research results indicated a more than double increase in the electroactive surface area; a decrease in the resistance of electron transfer on nanocomposite-modified CP, compared to bare CP. The phyto-AuNPs/PDDA-G/CP was used for the electrosensing of the synthetic dye Ponceau 4R. The oxidation signal of colorant enhanced 4-fold on phyto-AuNPs/PDDA-G/CP in comparison to CP. The effect of the quantity of nanomodifier, solution pH, potential scan rate, accumulation parameters, and differential pulse parameters on the peak current of Ponceau 4R was studied. Under optimal conditions, excellent sensory characteristics were established: LOD 0.6 nM and LR 0.001-2 μM for Ponceau 4R. High selectivity and sensitivity enable the use of the sensor for analyzing the content of Ponceau 4R in food products (soft drinks, candies, and popsicles) without additional sample preparation.

Recent advances in carbon nanomaterials-based electrochemical sensors for food azo dyes detection

Azo dyes as widely applied food colorants are popular for their stability and affordability. On the other hand, many of these dyes can have harmful impacts on living organs, which underscores the need to control the content of this group of dyes in food. Among the various analytical approaches for detecting the azo dyes, special attention has been paid to electro-analytical techniques for reasons such as admirable sensitivity, excellent selectivity, reproducibility, miniaturization, green nature, low cost, less time to prepare and detect of specimens and the ability to modify the electrode. Satisfactory results have been obtained so far for carbon-based nanomaterials in the fabrication of electrochemical sensing systems in detecting the levels of these materials in various specimens. The purpose of this review article is to investigate carbon nanomaterial-supported techniques for electrochemical sensing systems on the analysis of azo dyes in food samples in terms of carbon nanomaterials used, like carbon nanotubes (CNT) and grapheme (Gr).

Recent advances in Ponceau dyes monitoring as food colorant substances by electrochemical sensors and developed procedures for their removal from real samples

Ponceau dyes are one of the food coloring materials that are added to various pharmaceutical, health and food products and give them an appearance. These dyes contain contaminants such as Benzidine, 4-Aminobiphenyl, and 4-Aminoazobenzene that are safe in small amounts, but they are not approved by the US Food and Drug Administration (US-FDA) for human consumption. This study comprehensively was reviewed the properties, applications, chemistry, and toxicity of Ponceau dyes as food colorant substances. Electroanalysis of Ponceau dyes was discussed in detail, and the various electrochemical sensors used to detect and monitor these dyes as food colorant were examined. The applied methods of removing and degradation of these dyes in municipal and industrial wastes were also discussed. Conclusions and future perspectives to motivate future research were also explored.

Physical, Thermal and Biological Properties of Yellow Dyes with Two Azodiphenylether Groups of Anthracene

Two yellow bis-azo dyes containing anthracene and two azodiphenylether groups (BPA and BTA) were prepared, and an extensive investigation of their physical, thermal and biological properties was carried out. The chemical structure was confirmed by the FTIR spectra, while from the UV-Vis spectra, the quantum efficiency of the laser fluorescence at the 476.5 nm was determined to be 0.33 (BPA) and 0.50 (BTA). The possible transitions between the energy levels of the electrons of the chemical elements were established, identifying the energies and the electronic configurations of the levels of transition. Both crystals are anisotropic, the optical phenomenon of double refraction of polarized light (birefringence) taking place. Images of maximum illumination and extinction were recorded when the crystals of the bis-azo compounds rotated by 90° each, which confirms their birefringence. A morphologic study of the thin films deposited onto glass surfaces was performed, proving the good adhesion of both dyes. By thermal analysis and calorimetry, the melting temperatures were determined (~224-225 °C for both of them), as well as their decomposition pathways and thermal effects (enthalpy variations during undergoing processes); thus, good thermal stability was exhibited. The interaction of the two compounds with collagen in the suede was studied, as well as their antioxidant activity, advocating for good chemical stability and potential to be safely used as coloring agents in the food industry.

A Simple but Efficient Voltammetric Sensor for Simultaneous Detection of Tartrazine and Ponceau 4R Based on TiO2/Electro-Reduced Graphene Oxide Nanocomposite

In this work, we report a simple but efficient voltammetric sensor for simultaneous detection of ponceau 4R and tartrazine based on TiO2/electro-reduced graphene oxide nanocomposites (TiO2/ErGO). TiO2/ErGO nanocomposites were prepared by ultrasonically dispersing TiO2 nanoparticles (TiO2 NPs) into graphene oxide (GO) solution followed by a green in-situ electrochemical reduction. TiO2 NPs were uniformly supported on ErGO nanoflakes, which provides a favorable interface for the adsorption and subsequent oxidation of target analytes. TiO2/ErGO showed remarkable electrocatalytic capacity for the oxidation of ponceau 4R and tartrazine, with minimized oxidation overpotentials and boosted adsorptive striping differential pulse voltammetric (AdSDPV) response peak currents. Under the optimal experimental conditions, the anodic peak currents of ponceau 4R and tartrazine increase linearly with the respective natural logarithm of concentrations from 0.01 to 5.0 μM. The detection limits (LOD = 3σ/s) for ponceau 4R and tartrazine are 4.0 and 6.0 nM, respectively. The extraordinary analytical properties of TiO2/ErGO/GCE are primarily attributed to the synergistic enhancement effect from ErGO nanoflakes and TiO2 NPs. Moreover, the proposed TiO2/ErGO/GCE achieves reliable determination of ponceau 4R and tartrazine in orange juice with excellent selectively, reproducibility and stability. Together with simplicity, rapidness, and low cost, the proposed sensor demonstrates great potential for on-site detection of azo colorants.

Green tea extract assisted green synthesis of reduced graphene oxide: Application for highly sensitive electrochemical detection of sunset yellow in food products

The search to find simple, cost-effective, environmentally friendly method for synthesising of reduced graphene oxide (rGO) has motivated the use of various natural materials. Also, monitoring of sunset yellow (SY) level in foods due to the potential negative side effects is imperative. In this study, tea extract was explored as reducing and stabilizing agent for synthesising of rGO. The rGO modified carbon paste electrode (rGO/CPE) was used as a highly sensitive electrochemical sensor for the detection of SY. The rGO/CPE, due to the large surface area, showed strong enhancement effect on electrochemical oxidation of SY. Under optimized conditions, linear range between 0.05 and 10 µM with a detection limit of 27 nM could be achieved. The proposed sensor was used to determine the amount of SY in food products with satisfactory results, and the results were in good agreement with the results obtained by UV-Vis spectroscopy.

An electrochemical sensor for the determination of tartrazine based on CHIT/GO/MWCNTs/AuNPs composite film modified glassy carbon electrode

A novel nanocomposite film of chitosan/graphene oxide (CHIT/GO)/multi-walled carbon nanotubes (MWCNTs)/gold nanoparticles (AuNPs) was applied to fabricate glassy carbon electrode (CHIT/GO/MWCNTs/AuNPs/GCE) for the determination of Tartrazine (TZ), synthetic dyes in food products. The electrochemical sensors found it to be highly sensitive by combining the signal amplification properties of GO and the excellent electronic and antifouling properties of MWCNTs. The CHIT/GO/MWCNTs/AuNPs/GCE exhibited as superior electron transfer materials and possesses intercalation properties which provide synergistic influence on the increment of the current signals. The optimum conditions were found at pH 7, 30 s, and 0.3 Vs^-1. The modified GCE obtained with a linear response ranging from 10 to 100 mg mL^-1 (r² = 0.99037) with a sensitivity of 0.018 μA μM^-1. The limit of detection (LOD) and quantification obtained were 1.45 and 4.83 mg mL^-1, respectively. The determination of TZ in spiked samples was reliable with recovery percentage from 94.52 to 109.0%. The developed sensor successfully tested in the determination of TZ analyte in commercial candy, jelly, and soft drinks with acceptable results.

Morphology-dependent electrochemical sensing performance of metal (Ni, Co, Zn)-organic frameworks

To clarify the morphology effect of metal-organic frameworks (MOFs) on their electrochemistry as well as to explore their electrochemical applications, three MOFs with metal centers of nickel, cobalt, and zinc are synthesized. The used organic ligand is only 1,3,5-benzenetricarboxylic acid. Characterizations using Fourier Transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and electrochemical techniques reveal that these MOFs possess similar bonding properties, crystalline structures and phase purity, but various morphology and electrochemical activities, including their own redox behavior, electrochemical response toward redox probes and analytes in solutions. As a case study of analytes, voltammetry of Ponceau 4R is investigated on three MOFs. Its sensitive and selective monitoring is further achieved on nickel MOFs with a linear range from 0.5 to 150 nM and a detection limit of 80 pM. Therefore, the morphology of MOFs determines electrochemistry of MOFs and their electrochemical sensing applications.

A Zinc Oxide Nanoflower-Based Electrochemical Sensor for Trace Detection of Sunset Yellow

Zinc oxide nanoflower (ZnONF) was synthesized by a simple process and was used to construct a highly sensitive electrochemical sensor for the detection of sunset yellow (SY). Due to the large surface area and high accumulation efficiency of ZnONF, the ZnONF-modified carbon paste electrode (ZnONF/CPE) showed a strong enhancement effect on the electrochemical oxidation of SY. The electrochemical behaviors of SY were investigated using voltammetry with the ZnONF-based sensor. The optimized parameters included the amount of ZnONF, the accumulation time, and the pH value. Under optimal conditions, the oxidation peak current was linearly proportional to SY concentration in the range of 0.50-10 μg/L and 10-70 μg/L, while the detection limit was 0.10 μg/L (signal-to-noise ratio = 3). The proposed method was used to determine the amount of SY in soft drinks with recoveries of 97.5%-103%, and the results were in good agreement with the results obtained by high-performance liquid chromatography.

Extraction, Analytical and Advanced Methods for Detection of Allura Red AC (E129) in Food and Beverages Products

Allura Red AC (E129) is an azo dye that widely used in drinks, juices, bakery, meat, and sweets products. High consumption of Allura Red has claimed an adverse effects of human health including allergies, food intolerance, cancer, multiple sclerosis, attention deficit hyperactivity disorder, brain damage, nausea, cardiac disease and asthma due to the reaction of aromatic azo compounds (R = R′ = aromatic). Several countries have banned and strictly controlled the uses of Allura Red in food and beverage products. This review paper is critically summarized on the available analytical and advanced methods for determination of Allura Red and also concisely discussed on the acceptable daily intake, toxicology and extraction methods.