Tartrazine, the synthetic azo dye responsible for the bright yellow hue of countless soft drinks, candies, medicines and cosmetics, has long occupied an uneasy place on ingredient lists around the world. Labeled as E102 in Europe and Yellow 5 in the United States, the colorant is permitted by regulators but constrained by strict limits, and a growing body of research has linked excessive intake to allergic reactions, hyperactivity in children, and potential damage to organs ranging from the liver to the nervous system. Against that backdrop, two chemists from Sri Dharmasthala Manjunatheshwara College in Karnataka, India, have unveiled a new electrochemical sensor that promises to make routine screening for tartrazine faster, cheaper and more accessible than existing laboratory methods.
Writing in the journal Discover Electrochemistry, Annapoorna S. Bhat and Rajesh N. Hegde describe the construction of a carbon paste electrode modified with a zinc oxide–cerium dioxide nanocomposite, a material combination that dramatically boosts the electrode’s sensitivity to the dye. The work addresses a persistent analytical challenge: tartrazine appears in real foods alongside sugars, salts, vitamins and other colorants, and regulators such as the European Union’s Scientific Committee for Food and the Joint FAO/WHO Expert Committee on Food Additives set the acceptable daily intake at 7.5 milligrams per kilogram of body weight. Detecting whether products stay within that ceiling requires instruments capable of measuring vanishingly small concentrations without being fooled by the surrounding chemical clutter.
The team’s approach began with the synthesis of the nanocomposite itself. Using a straightforward co-precipitation method, the researchers combined solutions of cerium nitrate and zinc nitrate with ammonium oxalate, stirring the mixture for eight hours at room temperature before filtering, washing, drying and calcining the solid at 400 degrees Celsius for five hours. The result was an agglomerated structure of spherical particles and block-like shapes, which scanning electron microscopy and energy-dispersive X-ray analysis confirmed contained both zinc and cerium phases. Ultraviolet-visible spectroscopy added further confirmation, revealing characteristic absorption bands at 340 nanometers for the composite and 230 nanometers for cerium-oxygen charge-transfer transitions, while Fourier-transform infrared spectroscopy identified the distinctive ZnO stretching vibration at 482 inverse centimeters and the Ce-O vibration at 514 inverse centimeters.
Why pair these two particular oxides? The answer lies in their complementary electronic personalities. Zinc oxide is a wide-bandgap semiconductor prized for its high electron-transfer capability and thermal stability, and it furnishes an abundance of surface active sites where tartrazine molecules can adsorb. Cerium dioxide, meanwhile, is celebrated for its redox behavior, driven by surface defects and oxygen vacancies that shuttle charge with unusual efficiency. Together, the authors report, the composite synergistically increases surface area, accelerates electron transport and stabilizes the electrode, turning an ordinary carbon paste into a far more capable sensing platform.
The evidence for that enhancement is quantitatively clear. By cycling the bare and modified electrodes in a potassium ferricyanide solution and applying the Randles–Sevcik equation, the team calculated that the effective surface area grew from 0.016 square centimeters for the unmodified paste to 0.024 square centimeters after modification, a 50 percent increase. When tartrazine was introduced, the contrast was even more striking. In a pH 5.5 phosphate buffer, the unmodified electrode oxidized the dye at 0.948 volts with a weak peak current of 2.230 microamperes, whereas the nanocomposite-modified electrode delivered a current of 3.228 microamperes, roughly 1.44 times larger, indicating markedly faster electron transfer at the composite surface. The voltammograms showed only an oxidation peak and no reduction peak on the reverse scan, marking the process as electrochemically irreversible.
Optimizing the sensor required the researchers to fine-tune several experimental variables. The pH of the supporting electrolyte proved critical: scanning across buffers from pH 4.5 to 6.5, they found the strongest oxidation signal at pH 5.5, with the peak potential shifting linearly to less positive values as pH rose. The slope of that relationship, 34.8 millivolts per pH unit, pointed to the direct participation of a single proton in the oxidation mechanism. The proportion of nanocomposite in the paste also mattered. Testing loadings from 2.5 to 12.5 percent, the team observed a steady rise in signal up to 10 percent, where the greatest number of electroactive sites became available. Beyond that point, however, the particles began to agglomerate, obstructing electron transfer and dragging the current back down, so the 10 percent formulation was selected for all subsequent measurements.
Scan-rate studies fleshed out the kinetics of the process. As the scan rate climbed from 0.01 to 0.15 volts per second, the oxidation current grew in direct proportion to the rate itself, a signature of adsorption-controlled electron transfer. Applying Laviron’s analysis to the relationship between peak potential and the logarithm of scan rate, the researchers determined that approximately one electron, calculated as 1.32, participates in the oxidation of tartrazine, a finding consistent with a proton-coupled single-electron mechanism on the composite surface.
The analytical performance of the optimized electrode is the heart of the study. Using square-wave voltammetry, the team established a linear relationship between peak current and tartrazine concentration spanning 0.15 to 5 micromolar in the pH 5.5 buffer. From four independent calibration curves, with a standard deviation of 0.0106 and a slope of 0.3679, they calculated a limit of detection of 0.086 micromolar and a limit of quantification of 0.289 micromolar, figures that compare favorably with modified electrodes reported elsewhere in the literature. Selectivity was tested against common food-borne interferents, including sodium, potassium and calcium ions and ascorbic acid. The metal ions left the response essentially untouched, with recoveries between 3.7 and 4.5 percent deviation and relative standard deviations of 2 to 7 percent, while only elevated concentrations of ascorbic acid nudged the peak current slightly.
Crucially, the sensor was not confined to buffer solutions. The researchers applied it to two retail products purchased from local grocery shops in India, an orange-flavored instant drink mix and a custard powder, neither of which declares its tartrazine content on the label. Using the standard-addition method, they quantified 0.71 milligrams per liter of tartrazine in the drink mix and 0.82 milligrams per liter in the custard powder, with recoveries ranging from 91 to 110 percent and relative standard deviations between 1.8 and 8.7 percent across four measurements. Interestingly, an additional oxidation peak between 0.6 and 0.65 volts revealed the presence of Sunset Yellow, a second synthetic dye, in both samples, in agreement with the products’ ingredient declarations and demonstrating the electrode’s ability to flag multiple colorants in a single sweep.
The sensor also proved durable. Five measurements taken with freshly renewed electrode surfaces within a single day yielded a relative standard deviation of just 2.49 percent for the peak current, and over five consecutive days of testing the electrode retained 97.2 percent of its initial response, indicating robust storage stability. Taken together, the results sketch a practical vision for food safety monitoring: a simple, low-cost electrode that can be prepared from graphite powder, paraffin oil and a modest quantity of nanocomposite, then deployed with a portable electrochemical analyzer to check dye levels in minutes rather than hours. The authors conclude that the method provides a rapid and efficient route to tartrazine determination, one that could complement or even replace chromatographic techniques such as high-performance liquid chromatography in quality-control laboratories where affordability and speed matter as much as precision.
Subject of Research: Voltammetric detection of the synthetic food dye tartrazine using a ZnO–CeO2 nanocomposite-modified carbon paste electrode
Article Title: Development of ZnO–CeO2 modified carbon paste electrode for the voltammetric detection of tartrazine
Article References: Development of ZnO–CeO2 modified carbon paste electrode for the voltammetric detection of tartrazine. (n.d.). https://doi.org/10.1007/s44373-026-00155-w
Image Credits: AI Generated
DOI: 10.1007/s44373-026-00155-w
Keywords: tartrazine, food dye, ZnO–CeO2 nanocomposite, carbon paste electrode, voltammetry, electrochemical sensor, food safety, square-wave voltammetry, E102, nanomaterials, limit of detection, commercial food samples
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Bethany Barker. (September 23, 2026). Zinc–Cerium Nanocomposite Sensor Offers Rapid Detection of Controversial Yellow Food Dye. Scienmag. https://scienmag.com/zinc-cerium-nanocomposite-sensor-offers-rapid-detection-of-controversial-yellow-food-dye/
Bethany Barker. “Zinc–Cerium Nanocomposite Sensor Offers Rapid Detection of Controversial Yellow Food Dye.” Scienmag, 23 September 2026, https://scienmag.com/zinc-cerium-nanocomposite-sensor-offers-rapid-detection-of-controversial-yellow-food-dye/. Accessed 23 September 2026.
Bethany Barker. “Zinc–Cerium Nanocomposite Sensor Offers Rapid Detection of Controversial Yellow Food Dye.” Scienmag. September 23, 2026. https://scienmag.com/zinc-cerium-nanocomposite-sensor-offers-rapid-detection-of-controversial-yellow-food-dye/
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Tags: affordable food additive screening methodscarbon paste electrodecommercial food samplesE102electrochemical sensing of food colorantselectrochemical sensorfood dyefood safetyinnovative electrochemical sensors for E102 detectionlimit of detectionnanocomposite sensorsnanomaterial-based food safety testingnanomaterial-enhanced electrodes for food safetynanomaterialsnanotechnology in food quality controlrapid tartrazine detectionregulatory compliance testing for synthetic dyessensitive detection of Yellow 5 in consumablessquare-wave voltammetrytartrazinevoltammetryzinc oxide–cerium dioxide nanocomposite for dye analysisZinc–cerium nanocomposite food dye sensorZnO–CeO2 nanocomposite
