The researchers, led by Surendirakumar Kannaiah and Suguna Paramasivam, collected the fruit pedicel waste, known locally as sundakai kambu, from household kitchens in Pudukkottai, Tamil Nadu. After washing, shade-drying, and grinding the material into a coarse powder, they boiled ten grams of the powder in one hundred milliliters of distilled water at 65 degrees Celsius for one hour. The resulting pale-yellow extract was filtered and then added to a one millimolar solution of silver nitrate, the precursor salt supplying silver ions. Within twenty-four hours of incubation in the dark at room temperature, the mixture shifted in color from pale yellow to orange brown, a visible signature that silver ions had been reduced to metallic silver nanoparticles. The team designated the resulting material ST@AgNPs, reflecting the role of the Solanum torvum extract in their creation.

The chemistry behind this transformation lies in the phytochemical richness of the turkey berry plant. Solanum torvum, a wild relative of the eggplant consumed as a vegetable across Africa and Asia and used extensively in traditional medicine, contains abundant alkaloids, flavonoids, saponins, tannins, and glycosides. In green nanoparticle synthesis, these biomolecules perform two simultaneous jobs: they donate electrons to convert silver ions into neutral silver atoms that nucleate into particles, and they adsorb onto the growing particle surfaces as capping and stabilizing agents that prevent uncontrolled clumping. Fourier-transform infrared spectroscopy of the synthesized particles revealed absorption bands characteristic of O-H and C-H stretching vibrations, amide I bands from proteins, and phenolic and aromatic functional groups, confirming that a cocktail of plant metabolites coats each nanoparticle and governs its formation.

Optical characterization confirmed the success of the synthesis. Ultraviolet-visible spectroscopy showed a distinct surface plasmon resonance peak at 418 nanometers, within the expected 390 to 450 nanometer window for silver nanoparticles and absent from the starting materials. Surface plasmon resonance arises from the collective oscillation of conduction electrons excited by incoming light, and its position and shape report on particle size, distribution, and stability. The researchers also mapped how synthesis conditions affect yield. At acidic pH values of five and six, no meaningful absorption peak appeared because particles agglomerate rather than nucleate, while neutral pH proved optimal. Temperature profiling showed that 35 degrees Celsius encouraged particle formation while preserving the integrity of the heat-sensitive biomolecules, whereas temperatures above 55 degrees Celsius degraded the extract and lowered yields. Time-course measurements revealed that absorbance increased steadily with incubation, reaching a maximum reduction of silver ions around 72 hours.

Structural analysis painted a consistent picture of crystalline, roughly spherical particles. X-ray diffraction produced sharp reflections at 2-theta values of 38.72, 44.16, 63.12, 77.60, and 82.74 degrees, indexed to the (111), (200), (220), (311), and (222) planes of face-centered cubic metallic silver, matching the standard reference pattern for elemental silver. Applying the Debye-Scherrer equation to the diffraction peaks yielded a crystallite size of approximately 22.8 nanometers for the dominant (111) plane. Field-emission scanning electron microscopy showed spherical particles, some with irregular shapes, ranging from roughly 100 to 200 nanometers with mild agglomeration attributable to capillary forces during drying. Energy-dispersive X-ray analysis confirmed elemental silver as the dominant component at 42.46 percent, with an absorption signal near 3 kiloelectronvolts characteristic of metallic silver nanocrystals, alongside contributions from carbon, oxygen, chlorine, and sulfur residues of the plant capping layer.

Transmission electron microscopy resolved individual particles as isotropic spheres with some elliptical and aggregated forms, and the size distribution histogram derived from the images gave an average particle diameter of about 108 nanometers. Selected-area electron diffraction produced concentric rings of elemental silver, confirming high crystallinity. Dynamic light scattering and zeta potential measurements added a critical stability insight: the particles carried a surface charge of negative 16.2 millivolts. This negative charge, attributed to the bioorganic capping layer inherited from the plant extract, generates electrostatic repulsion between particles and keeps the colloid from settling or fusing. The authors note that the hydrodynamic size in this study is larger than the 20 to 27 nanometer particles previously reported from Solanum torvum fruit and root extracts, a difference likely reflecting the distinct phytochemical profile of pedicel tissue compared with other plant organs.

The biological performance of the nanoparticles was tested against four human pathogenic bacteria: the Gram-positive Staphylococcus aureus and Staphylococcus haemolyticus, and the Gram-negative Klebsiella pneumoniae and Pseudomonas aeruginosa. In agar well diffusion assays, activity rose with dose. At the highest concentration of 100 micrograms per milliliter, the nanoparticles produced inhibition zones of 18 millimeters against Staphylococcus aureus, 16 millimeters against Klebsiella pneumoniae, 15 millimeters against Pseudomonas aeruginosa, and 8 millimeters against Staphylococcus haemolyticus, with a clearly dose-dependent effect when compared against the standard antibiotic ampicillin. Broth dilution assays quantified the minimum inhibitory concentrations, yielding IC50 values of 68.54 micrograms per milliliter for Staphylococcus aureus, 53.12 for Klebsiella pneumoniae, 72.78 for Pseudomonas aeruginosa, and 81.40 for Staphylococcus haemolyticus, along with marked reduction of bacterial colony formation on agar plates even at the lowest tested doses.

The mechanism of this antibacterial action operates on several fronts. Silver nanoparticles bind to the negatively charged bacterial cell surface, disrupting membrane integrity and interfering with permeability, osmoregulation, electron transport, and respiration. Particles that penetrate the cell interact with DNA, proteins, and other phosphorus- and sulfur-containing biomolecules, triggering cellular dysfunction and death. In addition, the particles release silver ions that amplify the bactericidal effect in a size- and concentration-dependent manner. Because antibiotic resistance continues to erode the effectiveness of conventional drugs, metal nanoparticles are increasingly viewed as a promising platform for new antimicrobial coatings, wound dressings, food preservation systems, and antiseptic formulations, and the low minimum inhibitory concentrations observed here support that trajectory.

Perhaps the most striking result came from the cancer experiments. Using the MTT viability assay on A549 human lung adenocarcinoma cells, the team found that ST@AgNPs suppressed cell proliferation in a dose-dependent manner with an IC50 value of 38.2 plus or minus 0.8 micrograms per milliliter. For comparison, the clinical chemotherapy drug doxorubicin, used as the positive control, showed an IC50 of 24.3 plus or minus 1.05 micrograms per milliliter. While the plant-derived nanoparticles did not outperform the commercial drug, the authors emphasize that achieving potent cytotoxicity with a material synthesized from discarded kitchen waste, without toxic chemical reagents, represents a meaningful step toward affordable bioactive therapeutics. The team cautions that further clinical studies are needed before any therapeutic application, but the convergence of waste valorization, green chemistry, and demonstrated antibacterial and anticancer activity makes ST@AgNPs a compelling example of how nanotechnology can convert environmental liabilities into biomedical assets and advance a more circular bioeconomy.

Subject of Research: Green synthesis of antibacterial and anticancer silver nanoparticles from Solanum torvum fruit pedicel waste

Article Title: Antibacterial and cytotoxic effect of green synthesized silver nanoparticles using Solanum torvum fruit pedicel waste extract

Article References: Kannaiah, S., Paramasivam, S., Sanasam, B., Sekar, N., Nongthombam, K. S., Palanivel, K., & Pandiyan, J. (2026). Antibacterial and cytotoxic effect of green synthesized silver nanoparticles using Solanum torvum fruit pedicel waste extract. Discover Biotechnology, 3(1), Article 2. https://doi.org/10.1007/s44340-026-00049-y

Image Credits: AI Generated

DOI: 10.1007/s44340-026-00049-y

Keywords: silver nanoparticles, green synthesis, Solanum torvum, food waste valorization, antibacterial activity, A549 lung cancer cells, MTT assay, phytochemicals, zeta potential, nanobiotechnology, Turkey berry, sustainable nanomaterials

Indigo carmine, chemically known as disodium (2E)-3-oxo-2-(3-oxo-5-sulfonato-1,3-dihydro-2H-indol-2-ylidene)-5-indolinesulfonate, carries a molar mass of 466.36 grams per mole and appears throughout the textile, food, and pharmaceutical industries. Its high water solubility, aromatic structure, and sulfonate functional groups make it both persistent and difficult to strip from industrial effluents. Beyond aesthetic concerns, exposure carries documented risks including biotoxic effects and potential mutagenic and carcinogenic consequences, which makes effective treatment of dye-laden wastewater an environmental priority. Adsorption has long been considered one of the most attractive remediation routes because it is efficient, simple to operate, and inexpensive when low-cost or waste-derived materials are used.

The twist in this study lies in how the researchers deliberately avoided the chemistry that usually dominates when lithium manganese oxide meets this dye. Under acidic conditions, the spinel lattice of LiMn2O4 is redox-active: protons attack the structure, driving delithiation toward lambda-MnO2 and partial disproportionation to MnO, while manganese ions are reduced and the dye is oxidatively destroyed. Previous work, including earlier studies by the same group, exploited this acid-driven redox coupling for oxidative decolorization. But those experiments could not separate adsorption from chemical degradation. By working at pH 7 and pH 11, where manganese redox activity and acid-assisted lattice dissolution are suppressed, the team isolated purely surface-controlled interactions for the first time.

To build the adsorbent, the researchers manually disassembled commercial Nokia BL-4C cellphone batteries, chosen because their cathodes are predominantly LiMn2O4, and separated the cathode tape from the other components. A mild thermal pretreatment at 200 degrees Celsius for five hours in air was applied to volatilize residual organic solvents and electrolyte-derived species while preserving the spinel structure. The authors are careful to note that this step cannot remove polymeric binders such as PVDF, which degrade at higher temperatures, but scanning electron microscopy with energy-dispersive X-ray analysis showed a marked reduction in fluorine and phosphorus signals, consistent with partial cleaning of electrolyte residues such as LiPF6 and its decomposition products.

Characterization confirmed that the recovered material retained its essential identity. X-ray diffraction patterns indexed to the cubic spinel structure of LiMn2O4 in the Fd3-bar space group, matching the JCPDS reference 35-0782, and the pattern was essentially unchanged after dye uptake, showing no new crystalline phases or significant peak shifts. Fourier-transform infrared spectroscopy revealed Mn-O vibrational bands between 500 and 700 reciprocal centimeters characteristic of MnO6 octahedra in mixed Mn3+/Mn4+ valence states. After adsorption, new features appeared in the 900 to 1100 and 1480 to 1650 reciprocal centimeter regions, assigned to C-N and aromatic C=C stretching modes of the dye, alongside a broad 3100 to 3500 band reflecting hydrogen bonding between dye N-H and O-H groups and surface hydroxyl sites.

The quantitative heart of the study is the adsorption isotherm analysis. Using a fixed adsorbent dose of one gram per liter and dye concentrations from 10 to 100 milligrams per liter at 25 degrees Celsius, the Langmuir model fit the pH 7 data exceptionally well, yielding a monolayer capacity of 4.95 milligrams per gram with a correlation coefficient of 0.99. At pH 11, that capacity collapsed to just 0.13 milligrams per gram. Crucially, the Freundlich constant fell by nearly two orders of magnitude and the heterogeneity exponent dropped from 5.40 to 2.68, indicating weaker and less favorable adsorption under alkaline conditions, yet the high correlation coefficients at both pH values showed that the underlying adsorption mechanism remained intact.

The explanation for this dramatic pH dependence came from electrostatics rather than site loss. Zeta potential measurements showed that the recycled powder carries a point of zero charge near pH 3; above it, the surface becomes increasingly negative, ranging from about minus 20 millivolts at pH 7 to minus 60 millivolts at pH 11. Because indigo carmine exists predominantly as a dianionic IC2- species under these conditions, the increasingly negative surface electrostatically repels the dye, excluding it from the adsorption region. Applying a Poisson-Boltzmann-based electrostatic accessibility model in which the apparent Langmuir capacity scales with an exponential Boltzmann factor, the researchers found that matching the experimental capacity ratio required an effective dye charge of approximately minus 2.2, consistent with speciation diagrams showing the dianion accounts for roughly 95 percent of dissolved species even at pH 11.

Thermodynamics painted the picture of a physisorption-dominated process. The enthalpy change of 1.3 plus or minus 0.1 kilojoules per mole is small and positive, indicating a weakly endothermic interaction with no strong chemical bond formation. The entropy change of 100 plus or minus 2 joules per mole per kelvin is large and positive, reflecting the release of structured water molecules and counterions as the dye attaches to the surface. The resulting Gibbs free energy change of minus 28.5 plus or minus 0.6 kilojoules per mole at 298 kelvin confirms spontaneity, and the combination of low enthalpy with high entropy marks adsorption as entropy-driven rather than enthalpy-driven, the classic signature of physical adsorption on heterogeneous oxide surfaces.

Where the material truly distinguishes itself is durability. Although its maximum capacity trails many engineered adsorbents, including functionalized carbon nanotubes, modified graphene oxide composites, and mesoporous metal oxide nanoparticles, the recycled cathode maintained greater than 95 percent removal efficiency across repeated adsorption-regeneration cycles, retaining about 94 percent after 20 adsorption-desorption cycles with only 6 percent total efficiency loss. Regeneration involved simply filtering the powder and soaking it in dilute 0.01 molar hydrochloric acid for 24 hours. The weak physical binding that limits capacity also enables nearly complete dye desorption, minimizing irreversible fouling of active sites. Ultraviolet-visible spectroscopy reinforced the point: after adsorption, the characteristic dye bands at 610, 290, and 250 nanometers remained, merely diminished in intensity, showing the chromophore survived intact and no redox degradation or new degradation products formed.

The broader context makes the approach timely. Global production of spent lithium-ion batteries is projected to exceed 11 million tons by 2030, and cathode materials account for roughly 30 to 40 percent of battery mass while containing high-value metals and structurally robust oxides. Repurposing that waste stream as a functional water-treatment material embodies circular economy principles, converting an environmental liability into an asset. The authors position recycled LiMn2O4 not as a high-capacity engineered sorbent but as a low-cost, waste-derived, structurally stable, and reusable material whose performance hinges on electrostatic accessibility. By coupling isotherm modeling, thermodynamics, zeta potential measurements, and Poisson-Boltzmann theory, the study delivers something rarer than a new adsorbent: a quantitative framework predicting exactly how pH and surface charge govern dye uptake, a framework that could guide the rational deployment of recycled battery oxides in real wastewater treatment wherever near-neutral conditions prevail.

Subject of Research: Adsorptive removal of indigo carmine dye from water using recycled LiMn2O4 cathode material from spent lithium-ion batteries under non-redox conditions.

Article Title: Adsorptive removal of indigo carmine using recycled LiMn2O4 cathode material under non redox conditions

Article References: Garcia, E. M., Dias, T. M., Taroco, H. A., Melo, J. O. F., Mariz, C. S., & de Almeida Rocha, F. (2026). Adsorptive removal of indigo carmine using recycled LiMn2O4 cathode material under non redox conditions. Discover Industrial Chemistry and Materials, 1(1), Article 11. https://doi.org/10.1007/s44508-026-00012-z

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00012-z

Keywords: lithium-ion battery recycling, LiMn2O4, indigo carmine, adsorption, wastewater treatment, physisorption, electrostatic accessibility, zeta potential, Langmuir isotherm, circular economy, dye removal, recycled cathode material

The appeal of the technique lies in its simplicity. A cold plasma microjet is essentially a pencil-thin plume of ionized helium gas that remains close to room temperature even while it carries a menagerie of reactive species: electrons, ions, radicals, and energetic ultraviolet photons. When the researchers aimed this plume at magnesium wire submerged in liquid, the plasma’s chemistry attacked the metal surface, driving oxidation and dissolution reactions that ultimately precipitated magnesium hydroxide directly in the solution. Because no reducing chemicals are added at any stage, the process sidesteps many of the environmental and purification headaches associated with conventional wet-chemical nanoparticle synthesis, in which reagents such as sodium borohydride or organic solvents must later be removed from the final product.

To confirm that they had actually built what they intended to build, the team subjected their nanoparticles to a battery of characterization techniques. X-ray diffraction, which probes the arrangement of atoms by measuring how X-rays scatter from crystal planes, produced patterns that matched crystalline magnesium hydroxide exactly, and analysis of the peak widths revealed an average crystal size of approximately 10.5 nanometers. That is astonishingly small. For scale, a single human hair is roughly 7,000 times wider than one of these particles, and at that dimension the surface-to-volume ratio becomes enormous, meaning a large fraction of every particle’s atoms sit at the surface where they can interact directly with biological targets.

Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy provided the second pillar of evidence. The electron micrographs showed particles with a near-spherical morphology and a tight, uniform distribution, while the accompanying elemental analysis confirmed high chemical purity with no detectable contaminant phases introduced by the plasma process. Perhaps most importantly for any eventual biomedical use, zeta potential measurements returned values between +30 and +40 millivolts. Zeta potential is a measure of the electrical charge a particle presents to its surroundings, and values of this magnitude indicate strong electrostatic repulsion between neighboring particles. In practical terms, the nanoparticles resist clumping together and settling out of suspension, which means a stable, well-dispersed formulation can be prepared and stored without specialized stabilizers.

With the material thoroughly characterized, the researchers turned to the question that drives most of nanomedicine: what does it do to cancer cells? They exposed HeLa cells, a famous and hardy line of cervical cancer cells first isolated in 1951, to nanoparticle concentrations ranging from 0.025 to 1.0 parts per million, then measured cell viability using the MTT assay at 24, 48, and 72 hours. The MTT assay relies on the fact that metabolically active cells reduce a yellow tetrazolium compound into purple formazan crystals; the amount of purple dye produced is directly proportional to the number of living, functioning cells. It is one of the most widely trusted readouts of cytotoxicity in cell biology, and the results here followed a clear and reproducible pattern.

Cell viability dropped steadily as both concentration and exposure time increased, a dose- and time-dependent relationship that is exactly what one expects from a genuine cytotoxic agent rather than a measurement artifact. At the highest concentration after 72 hours, cytotoxicity exceeded 80 percent, meaning that more than four out of every five cancer cells in the treated cultures had lost viability. Under the microscope, the researchers documented the physical consequences of that toxicity: treated cells visibly shrank and their membranes showed signs of damage, morphological hallmarks consistent with progressive cellular collapse rather than a transient growth slowdown.

The mechanism behind magnesium hydroxide’s anticancer effect is not fully mapped, and the study’s authors are careful on this point, emphasizing that the molecular pathways involved still need to be elucidated in future work. The existing literature, however, offers several plausible leads. Magnesium hydroxide is mildly alkaline and slowly releases hydroxide ions, which can perturb the delicate pH homeostasis that tumor cells work hard to maintain. Prior studies have shown that magnesium hydroxide nanoparticles can physically damage bacterial cell walls, raising the possibility that similar mechanical stress on the more fragile membranes of cancer cells contributes to the observed membrane damage. Related magnesium oxide nanoparticles have been linked to elevated reactive oxygen species, oxidative stress being one of the classic triggers of programmed cell death. Disentangling these candidate mechanisms, and determining which dominates at the low parts-per-million concentrations used in this study, is the obvious next experimental frontier.

The researchers are equally candid about the most important caveat: selectivity. A compound that kills cancer cells but harms healthy cells equally well is simply a poison, not a therapy. This study evaluated cytotoxicity exclusively against HeLa cells, so the question of how the nanoparticles behave toward normal cervical epithelial cells, fibroblasts, or other healthy tissue types remains open. Earlier work on magnesium-based nanomaterials has often reported favorable biocompatibility profiles, and magnesium itself is a biologically essential element that the human body regulates and tolerates well, which gives the field reason for optimism. But optimism is not evidence, and the authors explicitly call for comparative studies against normal cell lines before any clinical relevance can be claimed.

If those selectivity studies succeed, the potential applications extend beyond anticancer therapy. Magnesium hydroxide nanoparticles have already attracted interest as antibacterial agents, wound-dressing components, and drug-delivery platforms, with prior reports describing magnesium hydroxide nanocomposite hydrogels for infected wound care and fluorescent magnesium hydroxide nanosheets for antimicrobial bandages that also monitor wound pH. A synthesis method that is cheap, green, and reproducible, as the cold plasma microjet route demonstrably is, lowers the barrier to producing the quantities of well-defined nanomaterial that such applications demand. The plasma approach also produces the particles in a single step from a metallic precursor, avoiding the surfactants, high temperatures, and prolonged hydrothermal processing that other routes require.

What makes the study genuinely notable, then, is the combination of three results that rarely appear together: an unusually clean and sustainable synthesis, a rigorously characterized and colloidally stable product, and a striking biological effect at remarkably low concentrations. Parts per million is an extraordinary range in which to see strong cytotoxicity, and if future work confirms that the effect is selective for transformed cells, cold-plasma-synthesized magnesium hydroxide nanoparticles could move from the physics lab toward preclinical evaluation. For now, the study stands as a persuasive demonstration that one of the most extreme tools in modern physics can craft one of chemistry’s humblest compounds into a serious candidate for cancer research, and it offers a template for how plasma science and biomedicine can be married to greener effect.

The choice of helium as the plasma-forming gas is itself worth noting. Helium’s high ionization energy and low breakdown voltage make it the workhorse gas for atmospheric-pressure plasma jets, producing a discharge that is dense in reactive oxygen and nitrogen species yet gentle enough to operate in open air near liquid surfaces. Researchers in the same laboratory group have previously applied this technique to other materials, including zinc oxide, copper oxide, iron oxide, and selenium nanoparticles, suggesting that the microjet platform functions as a general-purpose synthesis tool rather than a one-off method tailored to a single compound.

The positive surface charge reported for the particles also has biological implications beyond shelf stability. Positively charged nanoparticles generally interact more readily with the negatively charged membranes of mammalian cells, which can promote cellular uptake through endocytosis. Prior work on related magnesium-based nanomaterials has traced toxicity to caveolin-1-mediated endocytosis in endothelial cells, illustrating how surface charge and internalization pathways can shape a nanoparticle’s biological behavior.

The concentration range examined here deserves emphasis. At 0.025 to 1.0 parts per million, the effective doses are far below those typically reported for many metal oxide nanoparticles in similar assays, where tens or hundreds of parts per million are often required to achieve comparable killing. Whether this heightened potency reflects the small crystal size, the high purity, the colloidal stability, or some combination of these properties remains an open question that comparative studies against conventionally synthesized magnesium hydroxide could resolve.

It is also useful to place the safety picture in context. Animal studies of magnesium oxide nanoparticles have generally found limited acute toxicity, and investigations of magnesium hydroxide nanoparticles in normal biological systems have reported favorable biosafety profiles at antibacterial doses. That record, combined with magnesium’s status as an essential physiological element, provides a plausible foundation for the selectivity studies the authors now call for, though in vitro potency at parts-per-million levels will need careful re-examination in more complex biological systems before therapeutic claims can be entertained.

Subject of Research: Cold plasma synthesis of magnesium hydroxide nanoparticles and their in vitro cytotoxicity against HeLa cervical cancer cells.

Article Title: Cold Plasma Synthesis Mg(OH)₂ Nanoparticles: In Vitro Cytotoxic Evaluation Against HeLa Cervical Cancer Cells

Article References: saad akram, R., Majeed, N. F., Abdalameer, N. K., & Zaydan, E. A. (2026). Cold Plasma Synthesis Mg(OH)₂ Nanoparticles: In Vitro Cytotoxic Evaluation Against HeLa Cervical Cancer Cells. Journal of Medical and Biological Engineering. https://doi.org/10.1007/s40846-026-01055-5

Image Credits: AI Generated

DOI: 10.1007/s40846-026-01055-5

Keywords: cold plasma, magnesium hydroxide, nanoparticles, HeLa cells, cervical cancer, cytotoxicity, MTT assay, green synthesis, nanomedicine, biomedical engineering, X-ray diffraction, zeta potential

The study, led by Quéren Hapuque de Castro Novelli of the University of Campinas in São Paulo, together with colleagues from ImmunoCamp Science and Technology, the Adolfo Lutz Institute, and other Brazilian institutions, focused on a quantity known as the zeta potential. This is a measure of the electrical potential at the slipping plane surrounding a suspended particle, and it governs how particles interact with each other and with their chemical environment. When two surfaces carry like charges, they repel; when their charges are opposite, they attract. For parasite eggs, cysts, and oocysts suspended in fecal material, these electrostatic forces can determine whether the structures sediment to the bottom of a tube, float to the surface of a dense solution, bind to debris, or drift uselessly out of the operator’s field of view.

Standard diagnostic protocols for intestinal parasites—spontaneous sedimentation, centrifugal sedimentation using formalin with ether or ethyl acetate, and flotation techniques based on zinc sulfate, sodium chloride, or sucrose solutions—are designed around a single physical property: the density of the parasite structure. Yet the researchers point out that these methods largely ignore electrostatic forces and the inherent hydrophobicity of parasite surfaces, factors that can reduce recovery efficiency and contribute to the low-to-moderate sensitivity that plagues routine parasitology. The motivation for the new work was to quantify this neglected variable in structures taken directly, or in natura, from preserved fecal samples rather than from laboratory-cultured parasites under idealized conditions.

To obtain clean parasite material, the team screened samples submitted to the Ouro Verde Hospital Municipal Laboratory of Campinas, selecting those that tested positive with high infection intensity by the Kato-Katz method. The samples, preserved in 7.5 percent buffered formalin, were filtered through 400 and 200 micrometer meshes and then subjected to repeated cycles of dilution in deionized water and centrifugation at 490 times gravity for five minutes, a process repeated five times to strip away fecal debris and concentrate the parasite structures. Under a stereomicroscope, individual eggs and cysts were then captured with a 10 microliter micropipette and transferred to fresh tubes, a meticulous manual procedure repeated six times that ultimately yielded approximately 400 helminth eggs and more than 1,000 protozoan cysts completely free of contaminating fecal material.

Surface charge was then measured with a Malvern Zetasizer Nano ZS, an instrument that determines zeta potential from electrophoretic mobility. An electric field is applied across the sample cell, inducing charged particles to move at speeds proportional to their charge density. The instrument tracks this motion by analyzing Doppler shifts in laser light scattered by the moving particles: faster-moving particles produce larger frequency shifts, and from these shifts the electrophoretic mobility and the zeta potential are calculated. Each sample was analyzed in triplicate, and the instrument’s software classified every measurement as good quality, ruling out artifacts from bubbles, viscosity, or inadequate particle concentration.

The results were unambiguous. All three parasite species carried net negative surface charges, with values ranging across samples from −14.2 to −32.1 millivolts. Giardia duodenalis cysts proved the most strongly charged, averaging −28 millivolts, while Ascaris lumbricoides eggs averaged −21.9 millivolts and Taenia species eggs averaged −18.4 millivolts. Statistical comparison across species groups using ANOVA confirmed the significance of the measurements. Notably, this is the first study ever to report the surface charge of Ascaris lumbricoides and Taenia eggs, filling a long-standing gap in the physicochemical characterization of these globally important pathogens.

The findings align closely with earlier work on related organisms studied under controlled conditions. Previous research found that Cryptosporidium oocysts carry surface charges of around −38 to −40 millivolts and Giardia cysts around −17 to −35 millivolts, with charge becoming less negative as the surrounding medium grows more acidic. Studies of Ascaris suum eggs have shown that more than 70 percent of the egg surface is hydrophobic, a property explained by electron microscopy studies revealing the egg’s layered architecture: an outer proteinaceous membrane, a middle chitin layer, and an inner lipid layer. That layered composition likely underlies the negative charge and hydrophobic character observed in the present study as well.

The clinical significance of these numbers becomes clear when placed in the context of known diagnostic failures. The authors cite work on the formalin-ether concentration procedure showing that even when centrifugation force, time, solvents, and surfactants were systematically optimized, certain parasite species stubbornly resisted sedimentation—as though an invisible chemical force were acting against their movement through the suspension. The zeta potential measurements now provide a candidate explanation: repulsive electrostatic interactions between the negatively charged parasite surfaces and the surrounding medium or other negatively charged fecal particles can oppose the gravitational and density-driven forces on which sedimentation and flotation depend, keeping eggs and cysts suspended and out of the diagnostic sediment.

Understanding these surface properties also points toward solutions. One proposed alternative technique, dissolved air flotation, exploits surface charge directly by using carrier molecules adsorbed onto air bubbles to capture oppositely charged particles, which then rise to the surface for collection. Similar electrostatic logic underpins the successful use of paramagnetic microspheres to isolate Schistosoma mansoni eggs from feces and of immunomagnetic particles to capture Cryptosporidium oocysts. The authors suggest that ionic compounds capable of reducing the repulsive charges in fecal suspensions could replace some of the harsh and hazardous reagents currently used—saturated salt solutions that damage parasite morphology, and volatile solvents such as ether and ethyl acetate that pose risks to laboratory workers and the environment. Evidence from malaria research reinforces the principle: red blood cells infected with Plasmodium falciparum trophozoites exhibit a zeta potential of −14.6 millivolts, significantly lower than uninfected cells, promoting the cytoadherence that is central to the disease’s pathology.

Beyond improving today’s diagnostic protocols, the researchers argue that these first quantitative surface-charge data for Ascaris and Taenia eggs open the door to an entirely new generation of tools, including engineered nanoparticles designed to bind specifically to enteric pathogens based on their electrochemical signatures. In an era when intestinal parasites still disproportionately affect communities with poor sanitation, and when preventive chemotherapy faces the growing threat of anthelmintic resistance, even modest gains in diagnostic sensitivity could translate into meaningful public health benefits. By revealing the hidden electrostatic forces at play inside a routine stool specimen, this study gives laboratory scientists a physical parameter they have largely ignored for decades—and a concrete target for the diagnostic methods of the future.

The choice of formalin as a preservative deserves particular attention when interpreting these measurements. Buffered formalin has been the workhorse preservative of parasitology laboratories for generations because it fixes parasite morphology and halts decay without requiring refrigeration, making it practical in resource-limited settings where most infections occur. Yet fixatives can alter surface chemistry, cross-linking membrane proteins and changing the ionizable groups exposed at the particle surface. The fact that robust negative charges persisted even after formalin fixation suggests that the electrostatic character of these structures is stable and intrinsic, but it also means that measurements from fresh, unfixed specimens remain an open question for future work.

The zeta potential itself is not a direct reading of the membrane charge but an indirect inference made at the slipping plane, the boundary between the tightly bound ion layer around a particle and the diffuse layer that moves with it under an electric field. This is why factors such as ionic strength, pH, and temperature of the suspending medium all influence the measured value. The deionized water and dilute formalin used here create a low-conductivity environment that favors clean electrophoretic measurements, but real fecal suspensions are far more chemically complex, rich in bile salts, fatty acids, and electrolytes that can screen or modify surface charges. Translating these clean measurements to the messy reality of a diagnostic suspension is the next conceptual step.

The public health stakes are considerable. Soil-transmitted helminths such as Ascaris lumbricoides infect hundreds of millions of people worldwide, and Giardia duodenalis is among the most frequently identified causes of diarrheal illness in children in low-income regions. World Health Organization deworming programs depend on diagnostic stool examination both to map infection prevalence and to monitor the impact of mass drug administration, yet the modest sensitivity of conventional concentration techniques means true infection burdens are likely underestimated, particularly for light infections that fall below the detection threshold of a single slide.

There is also a methodological legacy worth noting: the sedimentation and flotation techniques in routine use today descend largely from methods formalized in the early twentieth century, refined empirically long before particle electrophoresis became accessible to parasitology laboratories. The present study exemplifies a broader trend of importing characterization tools from colloid science and environmental engineering into medical parasitology, a convergence that previously proved fruitful in water treatment research on Cryptosporidium and Giardia, where surface charge informed the design of filtration and coagulation processes for drinking water safety.

Subject of Research: Measurement of surface zeta potential charges of intestinal parasite eggs and cysts in preserved fecal samples and their impact on diagnostic separation techniques

Article Title: The Evaluation of Surface Charges of Ascaris Lumbricoides, Giardia Duodenalis, and Taenia spp., in Preserved Fecal Samples Processed in Natura

Article References: de Castro Novelli, Q. H., Soares, F. A., Margatho, V. S., Fernandes, E. P., Suzuki, C. T. N., Sabadini, E., dos Santos, B. M., de Melo, L. C. V., de Oliveira Baccin, A., Falcão, A. X., & Gomes, J. F. (2026). The Evaluation of Surface Charges of Ascaris Lumbricoides, Giardia Duodenalis, and Taenia spp., in Preserved Fecal Samples Processed in Natura. Acta Parasitologica, 71(5), Article 209. https://doi.org/10.1007/s11686-026-01367-1

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01367-1

Keywords: Ascaris lumbricoides, Giardia duodenalis, Taenia, zeta potential, surface charge, parasite diagnosis, fecal samples, sedimentation, flotation, electrophoretic mobility, hydrophobicity, parasitology