Electropolymerised-hemin-catalysed reduction and analysis of tartrazine and sunset yellow

Red-emissive carbon dot as fluorescent probe for the sensitive detection of sunset yellow in foodstuffs

The highly efficient red-emissive carbon dots (R-CDs) were synthesized from citric acid, polyethyleneimine, and benzil via a facile solvothermal process. The R-CDs displayed maximum fluorescence properties at excitation and emission wavelengths of 550 and 631 nm, respectively, which fall within the red wavelength range. Moreover, the R-CDs exhibited a high fluorescence quantum yield of 11.3 %, and this fluorescence was effectively quenched by Sunset Yellow (SY). Consequently, a novel fluorescent probe was developed for SY detection. This probe exhibited a linear range of 0.085-11.31 μg/mL and limit of detection of 0.026 μg/mL. The R-CDs were validated for SY quantification in various food samples, including carbonate beverages, powdered beverage, cider vinegar, fruit flavored drinks, chocolate, and hard candy samples, achieving recovery rates of 91.2-122 % and a relative standard deviation of 1.0-3.5 %. The synthesized R-CDs therefore show promise for application as a probe for the detection of SY in foods.

Facile incorporation of non-canonical heme ligands in myoglobin through chemical protein synthesis

The incorporation of non-canonical amino acids (ncAAs) into the metal coordination environments of proteins has endowed metalloproteins with enhanced properties and novel activities, particularly in hemoproteins. In this work, we disclose a scalable synthetic strategy that enables the production of myoglobin (Mb) variants with non-canonical heme ligands, i.e., HoCys and f4Tyr. The ncAA-containing Mb* variants (with H64V/V68A mutations) were obtained through two consecutive native chemical ligations and a subsequent desulfurization step, with overall isolated yield up to 28.6 % in over 10-milligram scales. After refolding and heme b cofactor reconstitution, the synthetic Mb* variants showed typical electronic absorption bands. When subjected to the catalysis of the cyclopropanation of styrene, both synthetic variants, however, were not as competent as the His-ligated Mb*. We envisioned that the synthetic method reported herein would be useful for incorporating a variety of ncAAs with diverse structures and properties into Mb for varied purposes.

Designing nano ranged electrode modifier comprised of samarium niobate anchored carbon nanofibers for trace level detection of food colourant: Tartrazine

Tartrazine (TRZ) is a predominantly used food color in food processing industries which is soluble in water to produce a orange colour. This food colorant is categorized under the mono-azo pyrazolone dye group known for the perilous azo group (-NN-) attached to the aromatic ring that threatens human health. In consideration of these aspects, a novel TRZ sensing platform with advanced electrode material is designed by incorporating nanotechnology with chemical engineering. This innovative sensor is prepared by electrode modification through a nano ranged electrode modifier of SmNbO₄ decorated on the enmeshed carbon nanofibers. This is the first report on the investigation of SmNbO₄/f-CNF as an electrode modifier to extricate the superlative electrochemical properties towards TRZ detection and protracted its practicality to food samples with a lower limit of detection (2 nmolL^-1), broad linear range, good selectivity, and functional stability.

Electropolymerized 4-Aminobenzoic Acid Based Voltammetric Sensor for the Simultaneous Determination of Food Azo Dyes

Electrochemical sensors with polymeric films as a sensitive layer are of high interest in current electroanalysis. A voltammetric sensor based on multi-walled carbon nanotubes (MWCNTs) and electropolymerized 4-aminobenzoic acid (4-ABA) has been developed for the simultaneous determination of synthetic food azo dyes (sunset yellow FCF and tartrazine). Based on the voltammetric response of the dyes' mixture, the optimal conditions of electropolymerization have been found to be 30-fold potential scanning between -0.3 and 1.5 V, at 100 mV s^-1 in the 100 µmol L^-1 monomer solution in phosphate buffer pH 7.0. The poly (4-ABA)-based electrode shows a 10.5-fold increase in its effective surface area and a 17.2-fold lower electron transfer resistance compared to the glassy carbon electrode (GCE). The sensor gives a sensitive and selective response to sunset yellow FCF and tartrazine, with the peak potential separation of 232 mV in phosphate buffer pH 4.8. The electrooxidation parameters of dyes have been calculated. Simultaneous quantification is possible in the dynamic ranges of 0.010-0.75 and 0.75-5.0 µmol L^-1 for both dyes, with detection limits of 2.3 and 3.0 nmol L^-1 for sunset yellow FCF and tartrazine, respectively. The sensor has been tested on orange-flavored drinks and validated with chromatography.

Sensitive Electrochemical Sensor Based On an Aminated MIL-101(Cr) MOF for the Detection of Tartrazine

The aminated metal-organic framework H₂N-MIL-101(Cr) was used as the carbon paste electrode (CPE) modifier for the determination of tartrazine (Tz) in soft drinks. The amino material was characterized by electrochemical impedance spectroscopy and showed significantly faster electron transfer with lower charge-transfer resistance (0.13 kΩ) compared to the electrode modified with the unfunctionalized MIL-101(Cr) material (1.1 kΩ). The H₂N-MIL-101(Cr)-modified CPE [H₂N-MIL-101(Cr)-CPE] was then characterized by cyclic voltammetry (CV) using [Fe(CN)₆]^3- and [Ru(NH₃)₆]³⁺ ions as the redox probes, showing good accumulation of [Fe(CN)₆]^3- ions on the electrode surface. A CV scan of Tz in Britton Robinson buffer solution revealed an irreversible system with an oxidation peak at +0.998 V versus Ag/AgCl/KCl. Using CV and differential pulse voltammetry, an electrochemical method for quantifying Tz in aqueous medium was then developed. Several parameters that affect the accumulation and detection steps were optimized. Optimal detection of Tz was achieved after 180 s of accumulation in Britton Robinson buffer solution (pH 2) using 2 mg of H₂N-MIL-101(Cr) material. Under optimal conditions, the sensor exhibited a linear response in the concentration range of 0.004-0.1 μM and good detection sensitivity (35.4 μA μM^-1), and the detection limit for Tz was found to be 1.77 nM (S/N = 3). Satisfactory repeatability, stability, and anti-interference performance were also achieved on H₂N-MIL-101(Cr)-CPE. The sensor was applied to commercial juices, and the results obtained were approximately similar to those given by UV-vis spectrophotometry.

Noncanonical Heme Ligands Steer Carbene Transfer Reactivity in an Artificial Metalloenzyme*

Changing the primary metal coordination sphere is a powerful strategy for tuning metalloprotein properties. Here we used amber stop codon suppression with engineered pyrrolysyl-tRNA synthetases, including two newly evolved enzymes, to replace the proximal histidine in myoglobin with N_δ -methylhistidine, 5-thiazoylalanine, 4-thiazoylalanine and 3-(3-thienyl)alanine. In addition to tuning the heme redox potential over a >200 mV range, these noncanonical ligands modulate the protein's carbene transfer activity with ethyl diazoacetate. Variants with increased reduction potential proved superior for cyclopropanation and N-H insertion, whereas variants with reduced E^o values gave higher S-H insertion activity. Given the functional importance of histidine in many enzymes, these genetically encoded analogues could be valuable tools for probing mechanism and enabling new chemistries.

Electropolymerized melamine for simultaneous determination of nitrite and tartrazine

Poly(melamine) (PMel) was synthesized via the electropolymerization of melamine monomer, which was then characterized by field-emission scanning electron microscopy (FESEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The possible polymerization mechanisms of melamine were also revealed by FT-IR spectroscopy and UV-Vis spectroscopy. Next, the PMel modified GCE (PMel/GCE) was used for the simultaneous determination of nitrite (NO₂^-) and tartrazine, and the parameters were optimized. The kinetic study showed that the electrochemical oxidation of nitrite and tartrazine at the surface of PMel/GCE is a typical surface-controlled electrode process. Under the optimun conditions, the developed sensor outperformed those previously reported, and it also exhibited high selectivity and reproducibility. Finally, the PMel/GCE was used for the simultaneous determination of nitrite and tartrazine in foodstuffs, and the results indicated that the proposed sensor could be a promising candidate for accurate determination of nitrite and tartrazine in real food samples.

Electrochemiluminescence Detection of Sunset Yellow by Graphene Quantum Dots

Use of food additives, such as colorants and preservatives, is highly regulated because of their potential health risks to humans. Therefore, it is important to detect these compounds effectively to ensure conformance with industrial standards and to mitigate risk. In this paper, we describe the preparation and performance of an ultrasensitive electrochemiluminescence (ECL) sensor for detecting a key food additive, sunset yellow. The sensor uses graphene quantum dots (GQDs) as the luminescent agent and potassium persulfate as the co-reactant. Strong and sensitive ECL signals are generated in response to trace amounts of added sunset yellow. A detection limit (signal-to-noise ratio = 3) of 7.6 nM and a wide linear range from 2.5 nM to 25 μM are demonstrated. A further advantage of the method is that the luminescent reagents can be recycled, indicating that the method is sustainable, in addition to being simple and highly sensitive.

Synthetic Food Dyes – Some Aspects Of Use And Methods Of Determination

Color is one of the key ingredients for increasing the appetizing of food, so food dyes have become firmly established in food production technologies. However, with the acquisition of toxicity data of synthetic food dyes (SFD), there were restrictions and standards for their content in food have emerged. Numerous papers published in recent years demonstrate the importance of the problem of the use and definition of SFD. The review contains over 180 literary references in the field of usage and methods of determination of synthetic food dyes, among them regulatory documents (regulations), official internet resources of international and Ukrainian organizations, review articles and original works. Varieties of chromatography, enzyme-linked immunoassay, optical and electrochemical methods are used to identify and determine SFD. Special attention was paid to voltammetry (VA) as a method that is cheaper than chromatography and completely satisfies selectivity, sensitivity, reliability requirements and is compatible with the concept of green analytical chemistry, as it doesn't need organic solvents. Moreover, single sweep voltammetry can be considered as a screening method with low limits of determination and rapid respons