MRI Contrast Agent Joins Zirconium Framework to Catch Banned Antibiotic in Food

Chloramphenicol is one of the most consequential antibiotic residues that food safety laboratories hunt for, and a research team in India has now built an unusual new tool to find it faster. In a study published in the journal Ionics, chemists at REVA University, B.M.S. College of Engineering, and Sir M.V. Government Science College describe a hybrid electrode that combines a zirconium-based metal-organic framework, a gadolinium-containing magnetic resonance imaging contrast agent called gadoteridol, and carbon fibers on a glassy carbon electrode. The composite, assembled with the help of ultrasonication, allowed the team to detect chloramphenicol down to a concentration of 0.2 micromolar with a reported sensitivity of 1.5 microamperes per micromolar per square centimeter. When the researchers spiked real food samples with the antibiotic, the sensor recovered it with high accuracy and standard deviations below five percent, a performance profile that suggests the approach could eventually migrate from the benchtop into routine residue screening.

The stakes behind this kind of analytical chemistry are higher than they might first appear. Chloramphenicol is a broad-spectrum antibiotic that once saw wide clinical use, including historic applications against pneumonic plague and typhoid, but it has been banned or tightly restricted in food-producing animals in many jurisdictions because residues in meat, milk, honey, and aquaculture products can pose direct toxic risks to consumers. Beyond acute toxicity, the presence of antibiotic residues in the food supply is one of the pressures that drives the emergence and spread of antimicrobial resistance, a public health threat that regulators worldwide now treat with mounting urgency. European regulations, including Commission Regulation (EU) 2019/1871 with its reference point for action and the monitoring framework of Regulation (EU) 2021/808, impose strict performance demands on any method used to police banned veterinary drug residues, which is precisely why faster, cheaper, and more portable detection platforms attract so much research attention.

Conventional methods for detecting chloramphenicol are powerful but cumbersome. Liquid chromatography coupled to mass spectrometry remains the gold standard for confirmatory analysis, and it has been applied to everything from honey to chicken muscle and eggs, often after dispersive solid-phase extraction or other cleanup steps. Capillary electrophoresis and high-performance liquid chromatography with ultraviolet detection have also been used, while immunoassays such as enzyme-linked immunosorbent assays offer screening capability at lower cost, and commercial ELISA kits have recently been comparatively assessed for meat and aquaculture products under the new European rules. Fiber optic chemiluminescent immunosensors and time-resolved fluorescence methods have pushed toward on-site use. Each of these techniques, however, typically involves sample preparation, instrumentation, trained operators, and turnaround times that are poorly matched to the pace of modern food distribution. Electrochemical sensors promise something different: direct electrical readout, small footprints, low reagent consumption, and the potential for field deployment.

The core of the new sensor is a zirconium metal-organic framework, a class of crystalline materials in which zirconium clusters are linked by organic struts into porous, cage-like architectures. Zr-MOFs have become favorites in the sensing literature because they combine high surface area with remarkable chemical and thermal stability, and they have already been engineered into platforms for detecting nitrofurazone, amoxicillin, tetracyclines, sulfonamides, and chlorpromazine, among other analytes. Recent reviews have highlighted zirconium-based frameworks as especially promising for food safety sensing. In the new work, the framework provides an abundance of adsorption and catalytic sites, while its ordered porosity concentrates chloramphenicol molecules near the electrode surface, amplifying the current signal that the electrochemical measurement records.

The second ingredient is the most surprising: gadoteridol, a gadolinium-based contrast agent that radiologists inject into patients to sharpen magnetic resonance images. Gadolinium complexes are prized in MRI because the gadolinium ion shortens the relaxation time of nearby water protons, brightening the image, and gadoteridol is one of the clinically approved macrocyclic agents with a well-characterized safety profile for that purpose. Its appearance in an electrochemical sensor reflects a growing recognition that gadolinium chemistry can do more than light up scans. Several recent studies have exploited gadolinium compounds for chloramphenicol detection, including gadolinium tungstate paired with sulfur-doped carbon nitride, nanostructured gadolinium tungstate on reduced graphene oxide, and iron-doped gadolinium oxide nanoparticles, all of which reported enhanced electron transfer and electrocatalytic activity. In the new composite, the gadoteridol component is proposed to contribute gadolinium-centered redox activity and electronic mediation that accelerates the reduction of chloramphenicol’s nitro group, the electrochemical fingerprint the sensor reads out.

The third component, carbon fiber, supplies the conductive backbone. Carbon-based nanomaterials have long served as electrode modifiers because they conduct electricity efficiently, resist corrosion, and present large accessible surfaces. Carbon fibers have previously been functionalized with polydopamine for chloramphenicol sensing, and carbon nanofibers decorated with zirconium dioxide have delivered strong analytical performance in earlier studies. In the hybrid architecture, the fibers interweave with the MOF crystals to form a percolating network that shuttles electrons from the catalytic sites to the underlying glassy carbon electrode, while the ultrasonication-assisted synthesis ensures the three phases are intimately mixed rather than simply layered on top of one another.

Characterization and electrochemical testing together tell the story of why the composite works. Scanning electron microscopy revealed the morphology of the hybrid material, X-ray diffraction confirmed its crystalline structure, and energy-dispersive X-ray analysis verified the elemental composition expected from the three components. The team then interrogated the electrode with the standard toolkit of electroanalysis: electrochemical impedance spectroscopy to measure how readily charge crosses the electrode-solution interface, cyclic voltammetry to map the redox behavior of chloramphenicol at the surface, and differential pulse voltammetry to achieve the fine discrimination needed for quantitative work at low concentrations. These techniques were used to systematically optimize the operating parameters, tuning the conditions under which the reduction signal for chloramphenicol is largest and cleanest.

The analytical figures of merit place the sensor among the competitive entries in a crowded field. A detection limit of 0.2 micromolar and a sensitivity of 1.5 microamperes per micromolar per square centimeter compare favorably with other recent chloramphenicol platforms, from tin oxide on reduced graphene oxide and tin-reduced graphene oxide screen-printed electrodes to nickel-cobalt MOF composites, molybdenum disulfide on carbon nanomaterials, cobalt oxide on graphene, and copper-molybdenum sulfide nanocomposites. Equally important for any sensor hoping to leave the laboratory, the electrode demonstrated strong selectivity against potential interferents, reproducibility from electrode to electrode, and operational stability over repeated measurements. The recovery experiments in food samples, with relative standard deviations under five percent, address the question that matters most to regulators: whether the sensor can find the antibiotic in the messy chemical company of a real food matrix rather than in a pristine buffer solution.

The study is not the team’s first foray into this territory. The same group has previously reported a graphene oxide, copper oxide, and zinc oxide nanocomposite combined with carbon fibers for chloramphenicol detection, and a molybdenum disulfide and carbon nanotube aerogel-based PEDOT nanocomposite for simultaneously detecting chloramphenicol and furazolidone in food. A related hybrid Zr-MOF, carbon nanotube, and nanocellulose sensor achieved dual detection of furazolidone and chloramphenicol. The new work extends that program by introducing a clinically validated MRI contrast agent into the electrode material itself, a design choice that highlights how researchers are increasingly raiding unexpected corners of chemistry, from diagnostic medicine to coordination polymers, in search of better electrocatalysts.

What comes next will determine whether the sensor remains an elegant laboratory demonstration or becomes a practical screening tool. The published work establishes the composite’s synthesis, characterization, and analytical performance, and the encouraging recovery rates in food samples point toward real-world applicability, but translating a modified glassy carbon electrode into a deployable device typically requires integration with portable potentiostats, disposable electrode formats such as screen-printed substrates, and validation across many more food types and laboratories. The broader context is favorable: regulators continue to tighten surveillance of banned veterinary residues, proficiency tests such as the Italian national reference laboratory’s exercise on chloramphenicol in honey underscore how demanding routine control can be, and the literature on Zr-MOF sensing platforms for food safety is expanding rapidly. If hybrid electrodes like this one can be manufactured reliably and cheaply, the unlikely marriage of an imaging drug, a porous zirconium framework, and carbon fiber may help put rapid antibiotic residue testing within reach of far more of the food supply chain than today’s chromatography suites can cover.

Subject of Research: Electrochemical detection of chloramphenicol antibiotic residues in food using a hybrid Zr-MOF/gadoteridol/carbon fiber composite electrode

Article Title: A Hybrid Zr-MOF/gadoteridol/carbon fiber composite glassy carbon electrode for rapid and sensitive electrochemical determination of chloramphenicol in food samples

Article References: R. B., R., Reddy, S., K.N., H., & Achary, G. (2026). A Hybrid Zr-MOF/gadoteridol/carbon fiber composite glassy carbon electrode for rapid and sensitive electrochemical determination of chloramphenicol in food samples. Ionics. https://doi.org/10.1007/s11581-026-07548-2

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07548-2

Keywords: chloramphenicol, Zr-MOF, gadoteridol, carbon fiber, electrochemical sensor, food safety, antibiotic residues, metal-organic frameworks, voltammetry, antimicrobial resistance, glassy carbon electrode, gadolinium