Simultaneous detection of sunset yellow and tartrazine using the nanohybrid of gold nanorods decorated graphene oxide

Trends in pulse voltammetric techniques applied to foodstuffs analysis: The food additives detection

Food additives are chemical compounds intentionally added during foodstuff production to control technological functions, such as pH, viscosity, stability (color, flavor, taste, and odor), homogeneity, and loss of nutritional value. These compounds are fundamental in inhibition the degradation process and prolonging the shelf life of foodstuffs. However, their inadequate employment or overconsumption can adversely affect consumers' health with the development of allergies, hematological, autoimmune, and reproductive disorders, as well as the development of some types of cancer. Thus, the development and application of simple, fast, low-cost, sensitivity, and selectivity analytical methods for identifying and quantifying food additives from various chemical classes and in different foodstuffs are fundamental to quality control and ensuring food safety. This review presents trends in the detection of food additives in foodstuffs using differential pulse voltammetry and square wave voltammetry, the main pulse voltammetric techniques, indicating the advantages, drawbacks, and applicability in food analysis. Are discussed the importance of adequate choices of working electrode materials in the improvements of analytical results, allowing reliable, accurate, and inexpensive voltammetric methods for detecting these compounds in foodstuffs samples.

Vivid-Colored Electrorheological fluids with simultaneous enhancements in color clarity and Electro-Responsivity

HYPOTHESIS

Surface modification of dielectric materials changes the dipole-dipole interactions under electric fields, thereby controlling the electrorheological (ER) response. The introduction of metal oxides onto mica templates and further coating of dyes is expected to simultaneously improve the color clarity and ER performance.

EXPERIMENTS

Dye-coated TiO2 platelets on mica are synthesized for high-performance colorful ER fluids. A sol-gel method is utilized to grow TiO2 on mica to prepare precursor light-colored mica/TiO2 materials, which are coated with appropriate dyes to enhance the vividness as determined by the Commission Internationale de clairage L*a*b* color system. The color expression and color clarity improvement are explained via the light interference effect and the presence of chromophores.

FINDINGS

The uniform TiO2 layers can be obtained under low pH conditions with controlled nucleation kinetics. The addition of dyes to TiO2 increases the surface area and porosity of ER materials and introduces heteroatoms that act as positive factors. In practical ER applications, dye-coated TiO2-based ER fluids exhibit higher ER performances compared with the corresponding light-colored TiO2-based ER fluids. The vivid-colored ER fluids could provide an easy selection for a wide range of rheological systems requiring a specific magnitude of stress by confirming the color.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

2D-ReS2 & diamond nanoparticles-based sensor for the simultaneous determination of sunset yellow and tartrazine in a multiple-pulse amperometry FIA system

We present a flow injection system with a multiple pulse amperometric detection (FIA-MPA)-based methodology for the simultaneous analysis of sunset yellow and tartrazine. As transducer, we have developed a novel electrochemical sensor based on the synergistic effect of ReS₂ nanosheets and diamond nanoparticles (DNPs). Among several transition dichalcogenides for the sensor development, we have selected ReS₂ nanosheets since it yields a better response towards both colourants. Scanning probe microscopy characterization shows that the surface sensor is composed by scattered and stacked ReS₂ flakes and large aggregates of DNPs. With this system, the gap between the oxidation potential values of sunset yellow and tartrazine is wide enough to allow the simultaneous determination of both dyes. Under the optimum potential pulse conditions (0.8 and 1.2 V) during 250 ms, a flow rate of 3 mL/min and a volume injection of 250 μL, detection limits of 3.51 × 10^-7 M and 2.39 × 10^-7 M for sunset yellow and tartrazine, respectively, were obtained. This method exhibits good accuracy and precision with Er minor than 13% and RSD lower than 8% with a sampling frequency of 66 samples per hour. Pineapple jelly samples were analyzed by the standard addition method, obtaining 53.7 mg/kg and 29.0 mg/kg of sunset yellow and tartrazine, respectively. From the analysis of fortified samples, recoveries of 94% and 105% were obtained.

An Electrochemical Sensor for Sunset Yellow Detection Based on Cu@Cu2O-BNPC Formed by Modified Porous Carbon

Control and detection of sunset yellow (SY) are an utmost demanding issue due to its high risk of detrimental effects on living systems caused by excessive ingestion. In this study, we reported the synthesis of Cu@Cu₂O nanoparticle-decorated B and N codoped porous carbon (BNPC) and its use in developing a novel electrochemical sensor for SY. The Cu@Cu₂O-BNPC catalyst was fabricated through single-step polymerization, followed by carbonization. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy characterization results showed that Cu@Cu₂O anchored on the porous BNPC successfully. Compared with the BNPC-modified electrode, it was found that the Cu@Cu₂O-BNPC-modified electrode showed superior electrocatalytic activity in both electrochemical impedance spectroscopy and cyclic voltammetry tests. The as-prepared Cu@Cu₂O-BNPC catalyst directly acted as a sensor for amperometric detection of SY without further assembling, which exhibited an ultrahigh sensitivity of 0.09 μA nM^-1 cm^-2, a low limit of detection (2.4 nM), and a wide linear detection ranging from 10 nM to 8 μM. To further validate its possible application, the proposed method was successfully used for the determination of SY in Fanta drinks with satisfactory results.

Optimization of uric acid detection with Au nanorod-decorated graphene oxide (GO/AuNR) using response surface methodology

A modified glassy carbon electrode (GCE) was developed based on a synthesized graphene oxide (GO) gold nanorod (AuNR) decorated composite (GO/AuNR) for sensitive electrochemical sensing of uric acid (UA). The electrochemical performance of GO/AuNR/GCE for UA detection was investigated employing the differential pulse voltammetry (DPV) technique. Central composite design (CCD) was applied to obtain the optimum composition of the GO and AuNR composite, which provide the highest possible UA oxidation peak current. The optimum composition was obtained at a GO concentration of 5 mg mL-1 and AuNR volume of 10 mL. Under the optimum conditions, GO/AuNR/GCE showed acceptable analytical performance for UA detection with good linearity (concentration range of 10-90 μM) and both a low detection limit (0.4 μM) and quantitation limit (1.0 μM). Furthermore, the proposed sensor exhibits superior stability, reproducibility, and selectivity using ascorbic acid (AA), dopamine (DA), urea, glucose, and magnesium as interferents. Finally, practical use of GO/AuNR/GCE was demonstrated by successfully determining the content of UA in human urine samples with the standard addition approach.

An Electrochemical Sensor Based on Carbon Paper Modified with Graphite Powder for Sensitive Determination of Sunset Yellow and Tartrazine in Drinks

The paper describes the development of an electrochemical sensor to be used for the determination of synthetic food colorants such as Sunset Yellow FCF (SY) and Tartrazine (TZ). The sensor is a carbon paper (CP) electrode, manufactured by using hot lamination technology and volume modified with fine-grained graphite powder (GrP). The sensor (GrP/CP) was characterized by scanning electron microscopy, energy dispersive spectrometry, electrochemical impedance analysis, cyclic, linear sweep and differential pulse voltammetry. The mechanism of SY and TZ electrochemical oxidation on GrP/CP was studied. The developed sensor has good electron transfer characteristics and low electron resistance, high sensitivity and selectivity. Applying the differential pulse mode, linear dynamic ranges of 0.005–1.0 μM and 0.02–7.5 μM with limits of detection of 0.78 nM and 8.2 nM for SY and TZ, respectively, were obtained. The sensor was used to detect SY and TZ in non-alcoholic and alcoholic drinks. The results obtained from drink analysis prove good reproducibility (RSD ≤ 0.072) and accuracy (recovery 96–104%).

Specific and Sensitive Detection of Tartrazine on the Electrochemical Interface of a Molecularly Imprinted Polydopamine-Coated PtCo Nanoalloy on Graphene Oxide

A novel electrochemical sensor designed to recognize and detect tartrazine (TZ) was constructed based on a molecularly imprinted polydopamine (MIPDA)-coated nanocomposite of platinum cobalt (PtCo) nanoalloy-functionalized graphene oxide (GO). The nanocomposites were characterized and the TZ electrochemical detection performance of the sensor and various reference electrodes was investigated. Interestingly, the synergistic effect of the strong electrocatalytic activity of the PtCo nanoalloy-decorated GO and the high TZ recognition ability of the imprinted cavities of the MIPDA coating resulted in a large and specific response to TZ. Under the optimized conditions, the sensor displayed linear response ranges of 0.003-0.180 and 0.180-3.950 µM, and its detection limit was 1.1 nM (S/N = 3). The electrochemical sensor displayed high anti-interference ability, good stability, and adequate reproducibility, and was successfully used to detect TZ in spiked food samples. Comparison of important indexes of this sensor with those of previous electrochemical sensors for TZ revealed that this sensor showed improved performance. This surface-imprinted sensor provides an ultrasensitive, highly specific, effective, and low-cost method for TZ determination in foodstuffs.

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).

Controllable synthesis of NiCo layered double hydroxide sheets on laser-induced graphene as electrodes for high-performance supercapacitors

NiCo-LDH@P12-LIG electrodes are prepared using the laser-induced graphene under hydrothermal conditions, showing an areal specific capacitance of 2072 mF cm−2.

Latest advances on the nanomaterials-based electrochemical analysis of azo toxic dyes Sunset Yellow and Tartrazine in food samples

Azo-dyes such as Allura Red, Carmoisine, Amaranth, Sunset Yellow (SY), Brilliant Blue, Tartrazine (Tz), etc., are popular as food coloring agents due to their low cost and stability. SY and Tz are the most used members of this group of dyes since they have similar colors and are usually used together in food products. Despite their advantageous industrial use, they exhibit a risk toxicity profile with adverse effects such as allergy, asthma, carcinogenicity, genotoxicity, cytotoxicity, anxiety, etc. Therefore, the United States Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) regulate the permissions for using these compounds to provide safe food products for consumers and prevent adverse effects both short and long-term. Considering all of these, for the analysis of azo toxic dyes, highly sensitive, low-cost, simple, and rapid sensors are necessary. Electrochemical nanosensors, which combine the unique features of electrochemistry and nanotechnology, are devices with all these advantages and are widely used for the determination of azo dyes. SY and Tz step forth as the most used food dyes in the class of azo-toxic dyes. They are often preferred together in food products, increasing the occurrence and exposure risk. Therefore, the analysis of Sunset Yellow and Tartrazine in food products has significant importance. In this review, the latest nanomaterial-based approaches for the electrochemical sensors on the analysis of SY and Tz in food samples were evaluated in terms of used nanomaterials and applied food samples.

Rational design of ultrahigh sensitive sunset yellow sensor based on 3D hierarchical porous graphitic carbon with sub-nanopores

The content of sunset yellow (SY) in food must be strictly controlled, because its excessive intake may cause many adverse health effects. Herein, we proposed an ultrasensitive SY sensor by using hierarchical porous graphitic (HPG) carbon derived from polyaniline hydrogel. After a first step of polymerization, the HPG carbon was prepared through carbonization and further chemical activation. In particular, the activation process endowed the HPG carbon with a high content of optimized porous architecture (sub-nanoporous surface area accounts for more than 90% of microporous surface area), and thus providing a structural basis for high efficiency of SY pre-concentration on HPG carbon surface. Therefore, the proposed sensor showed record-high sensitivity (5285.7 A M^-1 cm^-2) and ultra-low detection limit (0.15 nM), which represents a performance improvement in SY sensing. Furthermore, the sensor displays excellent selectivity, reproducibility and stability, exhibiting a great perspective in ultrasensitive monitoring of SY in commercial products.

Graphene Oxide-Coated Gold Nanorods: Synthesis and Applications

The application of gold nanorods (AuNRs) and graphene oxide (GO) has been widely studied due to their unique properties. Although each material has its own challenges, their combination produces an exceptional material for many applications such as sensor, therapeutics, and many others. This review covers the progress made so far in the synthesis and application of GO-coated AuNRs (GO-AuNRs). Initially, it highlights different methods of synthesizing AuNRs and GO followed by two approaches (ex situ and in situ approaches) of coating AuNRs with GO. In addition, the properties of GO-AuNRs composite such as biocompatibility, photothermal profiling, and their various applications, which include photothermal therapy, theranostic, sensor, and other applications of GO-AuNRs are also discussed. The review concludes with challenges associated with GO-AuNRs and future perspectives.

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

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2 min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50-1000 nM (R² = 0.996) and limit of detection (LOD) estimated to 19.2 nM (equivalent to 8.9 μg L^-1). The developed sensor possesses a very high sensitivity of 9 μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks. Graphical abstract.

A Novel Modified Electrode for Detection of the Food Colorant Sunset Yellow Based on Nanohybrid of MnO₂ Nanorods-Decorated Electrochemically Reduced Graphene Oxide

The nanohybrid of electrochemically-reduced graphene oxide (ERGO) nanosheets decorated with MnO₂ nanorods (MnO₂ NRs) was modified on the surface of a glassy carbon electrode (GCE). Controlled potential reduction was applied for the reduction of graphene oxide (GO). The characterization was performed by scanning electron microscopy, X-ray diffraction and cyclic voltammetry. Compared with the poor electrochemical response at bare GCE, a well-defined oxidation peak of sunset yellow (SY) was observed at the MnO₂ NRs-ERGO/GCE, which was attributed to the high accumulation efficiency as well as considerable electrocatalytic activity of ERGO and MnO₂ NRs on the electrode surface. The experimental parameters for SY detection were optimized in detail. Under the optimized experiment conditions, the MnO₂ NRs-ERGO/GCE showed good linear response to SY in concentration range of 0.01–2.0 μM, 2.0–10.0 μM and 10.0–100.0 μM with a detection limit of 2.0 nM. This developed method was applied for SY detection in soft drinks with satisfied detected results.

A multifunctional sensor for selective and sensitive detection of vitamin B12 and tartrazine by Förster resonance energy transfer

We used thiamine nitrate (TN) as single material to fabricate nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) with a quantum yield of 10.4% through one-pot hydrothermal method, and its properties were characterized by TEM, XPS, FTIR, fluorescence (FL) and UV-vis spectrophotometer, respectively. The fluorescence of N,S-CQDs was effectively quenched in the presence of vitamin B12 (VB12)/tartrazine due to Förster resonance energy transfer (FRET). Moreover, the rate (K_T) and efficiency (E%) of energy transfer from N,S-CQDs (as a donor) to VB12/tartrazine (as an acceptor) enhanced with increasing the concentrations of acceptor, and the K_T and E% were also varied with the change of excitation wavelengths (from 338 to 408 nm). Based on this principle, a multifunctional fluorescence probe was designed for selective and sensitive detection of VB12/tartrazine with a detection limit (3σ/slope) of 15.6/18.0 nmol/L. Meanwhile, the proposed method was successfully employed to detect VB12/tartrazine in milk and several beverages with a recovery range of 97.5-104.2%/91.0-110.6%.

Novel Electrochemical Sensors Based on Cuprous Oxide-Electrochemically Reduced Graphene Oxide Nanocomposites Modified Electrode toward Sensitive Detection of Sunset Yellow

Control and detection of sunset yellow is an utmost demanding issue, due to the presence of potential risks for human health if excessively consumed or added. Herein, cuprous oxide-electrochemically reduced graphene nanocomposite modified glassy carbon electrode (Cu₂O-ErGO/GCE) was developed for the determination of sunset yellow. The Cu₂O-ErGO/GCE was fabricated by drop-casting Cu₂O-GO dispersion on the GCE surface following a potentiostatic reduction of graphene oxide (GO). Scanning electron microscope and X-ray powder diffractometer was used to characterize the morphology and microstructure of the modification materials, such as Cu₂O nanoparticles and Cu₂O-ErGO nanocomposites. The electrochemical behavior of sunset yellow on the bare GCE, ErGO/GCE, and Cu₂O-ErGO/GCE were investigated by cyclic voltammetry and second-derivative linear sweep voltammetry, respectively. The analytical parameters (including pH value, sweep rate, and accumulation parameters) were explored systematically. The results show that the anodic peak currents of Cu₂O-ErGO /GCE are 25-fold higher than that of the bare GCE, due to the synergistic enhancement effect between Cu₂O nanoparticles and ErGO sheets. Under the optimum detection conditions, the anodic peak currents are well linear to the concentrations of sunset yellow, ranging from 2.0 × 10⁻⁸ mol/L to 2.0 × 10⁻⁵ mol/L and from 2.0 × 10⁻⁵ mol/L to 1.0 × 10⁻⁴ mol/L with a low limit of detection (S/N = 3, 6.0 × 10⁻⁹ mol/L). Moreover, Cu₂O-ErGO/GCE was successfully used for the determination of sunset yellow in beverages and food with good recovery. This proposed Cu₂O-ErGO/GCE has an attractive prospect applications on the determination of sunset yellow in diverse real samples.

Sensitive and Selective Detection of Tartrazine Based on TiO₂-Electrochemically Reduced Graphene Oxide Composite-Modified Electrodes

TiO₂-reduced graphene oxide composite-modified glassy carbon electrodes (TiO₂–ErGO–GCE) for the sensitive detection of tartrazine were prepared by drop casting followed by electrochemical reduction. The as-prepared material was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Cyclic voltammetry and second-order derivative linear scan voltammetry were performed to analyze the electrochemical sensing of tartrazine on different electrodes. The determination conditions (including pH, accumulation potential, and accumulation time) were optimized systematically. The results showed that the TiO₂–ErGO composites increased the electrochemical active area of the electrode and enhanced the electrochemical responses to tartrazine significantly. Under the optimum detection conditions, the peak current was found to be linear for tartrazine concentrations in the range of 2.0 × 10⁻⁸–2.0 × 10⁻⁵ mol/L, with a lower detection limit of 8.0 × 10⁻⁹ mol/L (S/N = 3). Finally, the proposed TiO₂–ErGO–GCEs were successfully applied for the detection of trace tartrazine in carbonated beverage samples.

A New Laccase Based Biosensor for Tartrazine

Laccase enzyme, a commonly used enzyme for the construction of biosensors for phenolic compounds was used for the first time to develop a new biosensor for the determination of the azo-dye tartrazine. The electrochemical biosensor was based on the immobilization of laccase on functionalized methacrylate-acrylate microspheres. The biosensor membrane is a composite of the laccase conjugated microspheres and gold nanoparticles (AuNPs) coated on a carbon-paste screen-printed electrode. The reaction involving tartrazine can be catalyzed by laccase enzyme, where the current change was measured by differential pulse voltammetry (DPV) at 1.1 V. The anodic peak current was linear within the tartrazine concentration range of 0.2 to 14 μM (R² = 0.979) and the detection limit was 0.04 μM. Common food ingredients or additives such as glucose, sucrose, ascorbic acid, phenol and sunset yellow did not interfere with the biosensor response. Furthermore, the biosensor response was stable up to 30 days of storage period at 4 °C. Foods and beverage were used as real samples for the biosensor validation. The biosensor response to tartrazine showed no significant difference with a standard HPLC method for tartrazine analysis.

Gold nanrods plasmon-enhanced photoelectrochemical aptasensing based on hematite/N-doped graphene films for ultrasensitive analysis of 17β-estradiol

It remains a vital task to establish ultrasensitive sensing interfaces for detection of target analytes to meet the demands of modern analysis. Herein, a highly sensitive turn-on photoelectrochemical (PEC) platform for trace 17β-estradiol (E2) assay was developed based on Au nanrods (AuNRs) with surface plasmon resonance (SPR) properties induced signal amplification. Specifically, a ternary hybrid was prepared by integrating hematite (α-Fe₂O₃) nanocrystals and N-doped graphene (NG) with AuNRs, which further served as highly efficient photoactive species. Subsequently, a PEC sensing platform was fabricated based on the specific binding of E2 and its aptamer. On such a sensor, the capture of E2 molecules by aptamers led to increased photocurrent. This was attributed to that the specific recognition reaction between E2 and aptamer resulted in the conformational change of the aptamers and complete dissociation of some aptamers on the PEC sensing interface. It can be confirmed by the electrochemical impedance spectroscopy (EIS) results. This process decreased the steric hindrances between the electrode surface and solution and thus increased the photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibited superb analytical performances for detection of E2 in the range from 1×10^-15M to 1×10^-9M with a detection limit of 3.3×10^-16M. The aptasensor manifested outstanding selectivity towards E2 when other endocrine disrupting compounds with similar structure coexisted. Furthermore, the aptasensor was successfully applied for the determination of E2 in milk powder. The present strategy provides a potential way to boost the activity of photoactive materials and improve the sensitivity of PEC biosensor.