Chloramphenicol is a broad-spectrum antibiotic that has become a poster child for a growing class of environmental contaminants known as active pharmaceutical ingredients. These compounds slip into rivers, lakes, and groundwater through hospital effluents, pharmaceutical plant discharges, improperly discarded medications, landfill leachate, and urban runoff. Detected universally at trace concentrations ranging from nanograms to micrograms per liter, they resist conventional treatment. Chloramphenicol is particularly worrying because of its limited biodegradability, cytotoxicity, potential to drive antimicrobial resistance, and capacity for endocrine disruption even at vanishingly low levels. Standard remedies, from biological degradation and coagulation to ozonation and activated carbon adsorption, each carry drawbacks: they can be compound-specific, energy-intensive, incomplete, or prone to generating toxic transformation products.

The core challenge, the authors note, lies in the complex physicochemical behavior of pharmaceuticals in water. Many behave as weak acids whose charge state shifts with pH, turning from neutral molecules into negatively charged species as acidity drops. That shift can trigger electrostatic repulsion between contaminant and adsorbent, gutting removal efficiency. At trace levels, weak driving forces and competition from natural organic matter and coexisting ions compound the problem. What is needed, the researchers argue, is a multifunctional, magnetically recoverable adsorbent that can grab antibiotics quickly, selectively, and repeatedly under realistic conditions.

Enter iron oxide. Magnetite, or Fe3O4, has long attracted attention in water treatment because it does double duty: it adsorbs contaminants and, thanks to its magnetic character, can be pulled out of treated water with a simple magnet, eliminating the need for filtration or centrifugation. But bare magnetic nanoparticles come with a notorious flaw. They aggregate, clumping together and sacrificing the very active surface area that makes them useful, while also being awkward to handle and reuse. Embedding them in a polymer matrix solves much of this, providing structural stability and dispersing the particles across a larger working surface.

The team’s material is a composite of polystyrene, cellulose acetate, and Fe3O4 nanoparticles, dubbed PS+CA@Fe3O4. Fabrication begins with dissolving polystyrene and cellulose acetate in warm dimethylformamide, then dispersing the nanoparticles with vigorous stirring followed by ten minutes of probe sonication to break up agglomerates. The homogeneous suspension is then electrospun: pushed through an 18-gauge needle at 1.8 milliliters per hour under a 12-kilovolt electric field toward a rotating drum collector positioned 12 centimeters away. After roughly two to two-and-a-half hours of collection and an overnight vacuum dry at 40 degrees Celsius, the result is a fluffy, cotton-like magnetic polymeric adsorbent rather than the dense membrane most electrospinning studies aim to produce.

The deliberate choice to operate at low polymer concentration is the study’s central insight. Insufficient chain entanglement means the spinning jet cannot sustain a continuous, smooth fiber, so bead-on-string morphology emerges instead. Where conventional wisdom sees failure, the researchers see function. The spherical bead domains act as localized adsorption microenvironments rich in accessible surface, while the connecting nanofibers maintain structural connectivity throughout the network. The resulting low-density, loosely packed three-dimensional architecture offers a variety of pore sites, reduced packing density, and shortened diffusion pathways, all of which accelerate mass transfer and give chloramphenicol molecules more chances to encounter active sites on the polystyrene, cellulose acetate, and magnetite components.

A battery of characterization techniques backs up the design. Field-emission scanning electron microscopy revealed the interwoven fibrous network studded with bright-contrast spots indicating well-dispersed Fe3O4. Fourier-transform infrared spectroscopy confirmed the coexistence of all three components, with a fingerprint band near 540 to 600 wavenumbers marking Fe-O stretching from embedded magnetite. X-ray diffraction showed sharp peaks matching the spinel cubic magnetite phase with no impurity phases such as maghemite or hematite, while the amorphous polymer matrix showed up only as a featureless baseline. X-ray photoelectron spectroscopy found the surface composed of roughly 90.68 percent carbon, 6.87 percent oxygen, and 2.45 percent iron, consistent with a polymer-dominated surface carrying iron-containing species. Nitrogen adsorption measurements classified the material as mesoporous, with a BET surface area of 19.36 square meters per gram, an average pore diameter of 31.36 nanometers, and a pore volume of 0.167 cubic centimeters per gram.

Two further measurements illuminate why the material works so fast. Contact angle tests showed pristine polystyrene fibers are strongly hydrophobic at 135.09 degrees, but the composite drops to 85.50 degrees, a shift the authors attribute to oxygen-containing cellulose acetate groups. That enhanced wettability lets water move freely through the structure, speeding delivery of contaminant molecules to active sites. Meanwhile, vibrating sample magnetometry recorded saturation magnetization of about 84 electromagnetic units per gram for pure Fe3O4 and about 48 for the composite, the reduction reflecting dilution by the nonmagnetic polymer. Crucially, both samples showed negligible remanence and low coercivity, a soft-magnetic, near-superparamagnetic character that means the spent adsorbent can be recovered cleanly with a magnet and will not clump together on its own.

Adsorption performance lived up to the architectural promise. In batch experiments across initial chloramphenicol concentrations of 50 to 120 parts per million, removal climbed rapidly within the first 30 to 40 minutes, reaching roughly 70 to 80 percent for all concentrations before plateauing as available sites filled. Kinetic modeling told a clear mechanistic story: the pseudo-second-order model fit superbly, with correlation coefficients between 0.9971 and 0.9997 across the full concentration range, while the pseudo-first-order model lagged behind. That pattern points to chemisorption, surface-controlled uptake governed by site availability, likely through pi-pi stacking between the aromatic rings of polystyrene and the antibiotic, hydrogen bonding between chloramphenicol’s hydroxyl and amide groups and cellulose acetate’s oxygen functionalities, and possible electrostatic interactions. Diffusion analysis with Boyd’s model suggested external film diffusion and surface adsorption jointly control the rate, with intraparticle diffusion playing a secondary role. Equilibrium data were best described by the Langmuir isotherm, indicating predominantly monolayer adsorption, with a maximum capacity of 22.42 milligrams per gram, a figure that edges out biochars, modified clays, molecularly imprinted magnetic chitosan polymers, and carbon nanotubes reported in the literature, which top out between 10 and 21.35 milligrams per gram.

The authors are candid about the limits of their evidence. The XPS analysis was survey-level and performed only on the pristine adsorbent, so the proposed molecular interactions, while chemically plausible, remain to be confirmed by post-adsorption spectroscopy, and no direct control comparison against bead-free fibers of identical composition was included. Still, the conceptual contribution stands on its own: a defect-to-function design philosophy that treats electrospinning’s morphological instability as a tunable engineering variable rather than a nuisance. The adsorbent also showed excellent reusability and stability in the study, and its magnetic recovery addresses one of the biggest practical headaches of nanoparticle-based water treatment. The researchers caution that chloramphenicol served as a single model contaminant, and that testing in mixed pharmaceutical systems, real wastewater matrices, and continuous-flow modules is the necessary next step. If those trials succeed, the lesson of this work could ripple far beyond one antibiotic: sometimes the fastest route to a better material is not eliminating the flaw, but learning what the flaw is for.

Subject of Research: Electrospun magnetic polystyrene-cellulose acetate nanofibrous adsorbents for chloramphenicol removal from water

Article Title: Exploiting electrospinning-induced bead-on-string morphology for enhanced surface accessibility and chloramphenicol adsorption onto magnetic nanofibrous adsorbents

Article References: Ranjan, R., Kullappan, M., Gumfekar, S. P., & Sabapathy, M. (2026). Exploiting electrospinning-induced bead-on-string morphology for enhanced surface accessibility and chloramphenicol adsorption onto magnetic nanofibrous adsorbents. Results in Chemistry, 31, Article 103918. https://doi.org/10.1016/j.rechem.2026.103918

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103918

Keywords: electrospinning, bead-on-string morphology, chloramphenicol, magnetic adsorbent, Fe3O4 nanoparticles, water treatment, pharmaceutical pollution, adsorption kinetics, polystyrene, cellulose acetate, nanofibers, antimicrobial resistance

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