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

PVDF is a semicrystalline fluoropolymer prized for its chemical resistance, thermal robustness, mechanical durability, and innate hydrophobicity. It is also polymorphic, crystallizing in phases that include the nonpolar alpha form and the piezoelectric beta phase, a combination that makes it attractive for filtration membranes, sensors, energy harvesters, and water-oil separation systems. The Brazilian group, led by Gabriel da Cruz Dias of the Universidade Estadual de Maringá together with colleagues at UNESP and UNIFUNEC, asked a question that most prior studies had avoided: what happens when clay content climbs far beyond the low loadings, typically at or below 10 percent by weight, that researchers usually dare to use?

The answer required an unconventional fabrication route. Electrospinning, the dominant method for producing polymer nanofibers, relies on high electric fields, delivers modest production rates, and is difficult to scale. Solution Blow Spinning instead uses a pressurized gas jet to draw fibers from a polymer solution, offering higher throughput, simpler equipment, and lower cost. In the experiments, PVDF was dissolved in N,N-dimethylformamide at a concentration of 30 percent weight per volume, and montmorillonite K10 clay was dispersed in the solvent beforehand at levels of 3, 5, 10, 20, and 30 percent relative to the polymer mass. The mixture was fed through the nozzle at 76 microliters per minute under an air pressure of 140 kilopascals, with a working distance of 21 centimeters, yielding self-supported fibrous mats whose average fiber diameters stayed below 200 nanometers.

Scanning electron microscopy revealed that pure PVDF fibers were uniform, smooth, and cylindrical, with only occasional bead defects caused by jet instability and incomplete solvent evaporation. As clay content rose, imperfections multiplied. At 30 percent loading, clay clusters became prominent, hanging from the fibers like stones tied to a string and, according to the authors’ vivid analogy, pulling the loaded jets toward the collector faster than the polymer threads could follow. The consequence was measurable: with a constant 5 milliliters of solution for every production run, composite thickness fell only slightly up to 10 percent clay but dropped considerably at 20 and 30 percent, signaling that the process was losing efficiency as aggregates sabotaged fiber deposition.

Perhaps counterintuitively, the viscosity of the spinning solutions decreased as more clay was added. The explanation lies in sample preparation: because the clay was first dispersed in DMF, higher clay concentrations demanded additional solvent, and this dilution effect outweighed the thickening expected from suspended solid particles. Thinner solutions allowed polymer chains to disentangle and stretch more easily under the constant air pressure, producing finer fibers at high clay contents. Up to 10 percent clay, where solvent content remained constant, the trend reversed, with diameters rising slightly as viscosity increased—behavior consistent with earlier electrospinning and blow-spinning studies of clay-laden polymer solutions.

Elemental mapping by energy-dispersive X-ray spectroscopy confirmed that silicon, oxygen, and aluminum from the clay were distributed fairly homogeneously through the fibrous networks, with localized clustering at the two highest loadings. X-ray diffraction showed that both the alpha and beta crystalline phases of PVDF coexisted in every mat and, crucially, that clay addition did not alter this balance. The researchers attribute the phase formation to the blow-spinning process itself, in which rapid solvent evaporation favors the alpha phase while simultaneous fiber stretching promotes the beta phase, and they note that room-temperature processing may explain why clay did not act as the beta-phase nucleation catalyst reported in studies using heated routes. Differential scanning calorimetry reinforced the structural picture, showing a single melting peak near 176 degrees Celsius for all compositions, with a shoulder attributed to melting of the interfacial region between crystalline and amorphous lamellae.

Thermogravimetric analysis, however, delivered a caution. Pure PVDF remained stable to roughly 420 degrees Celsius before losing about 75 percent of its mass through dehydrofluorination, the reaction that releases hydrogen fluoride and leaves behind unsaturated carbon species. The composites degraded in two steps, and an initial degradation peak intensified with clay content, evidence that dispersed rather than exfoliated clay particles, and particularly the metal ions within them, catalyzed chain scission. Without the barrier effect that well-exfoliated clay layers would provide, higher filler contents reduced the composite’s thermal stability rather than enhancing it.

Mechanical testing traced a clear arc from reinforcement to collapse. Pure PVDF membranes were highly ductile, stretching about 58 percent before breaking with an elastic modulus near 13 megapascals, behavior typical of fibrous mats in which fibers align and reorient under load. Adding up to 5 percent clay increased both stiffness and tensile strength, because rigid particles acted as bridging points that transferred stress between neighboring fibers. Beyond roughly 5 to 10 percent, however, performance deteriorated sharply: elongation at break fell steadily with filler content, and at 30 percent clay the tensile strength had dropped by about 54 percent relative to pure PVDF. The culprit, visible in both electron micrographs and elemental maps, was agglomeration—defects that concentrate stress and sever efficient load transfer through the network.

Wettability measurements added an unexpected twist. All composites remained hydrophobic, with static water contact angles of 114 degrees for pure PVDF and, apart from a slight dip at 3 percent clay, rising values of 115, 119, 122, and 123 degrees as clay content climbed to 5, 10, 20, and 30 percent. Because montmorillonite is inherently hydrophilic, the trend runs against intuition, but the authors attribute it to increased surface roughness imparted by clay particles, which amplifies the low surface energy conferred by PVDF’s strongly bonded carbon-fluorine groups. A water-ethanol mixture reduced the contact angles, offering a simple lever for tuning wettability in applications such as filtration and separation without changing the material’s composition.

The study’s broader message is twofold. First, Solution Blow Spinning is a genuinely viable and scalable route to PVDF-based fibrous nanocomposites, producing sub-200-nanometer fibers at productivity levels electrospinning cannot match—here, 5 milliliters of a 30 percent solution yielded mats roughly 500 micrometers thick. Second, the technique’s tolerance for inorganic fillers has hard limits. The 30 percent formulation, with its thin, fragile mats, abundant aggregates, and depressed mechanical performance, marks a boundary that future work should not cross without improved dispersion strategies. For now, the sweet spot sits at low clay contents, where composites combine hydrophobic surfaces, controllable porosity, and enhanced stiffness, positioning them for filtration, environmental remediation, and membrane applications. The authors suggest that next steps should focus on refining filler dispersion, optimizing processing parameters, and evaluating functional metrics such as permeability, selective adsorption, and long-term stability under realistic operating conditions.

Beyond the specific findings, the study offers a useful methodological template for anyone probing the limits of high-throughput fiber fabrication. Rather than presenting a single optimized formulation, the authors deliberately swept a wide compositional range and documented where each characterization technique registered a change in behavior. This threshold-mapping approach—tracking solution viscosity, fiber diameter, mat thickness, crystalline phase content, degradation onset, tensile response, and contact angle as a function of filler loading—makes the results directly comparable across laboratories and provides benchmarks against which future dispersion strategies can be judged.

The work also situates itself within a broader shift in fibrous membrane research. Electrospinning remains the reference technique for producing submicron polymer fibers, but its dependence on high voltages and modest throughput has long constrained industrial adoption. Solution Blow Spinning, by contrast, requires only a pressurized gas supply, a syringe pump, and a rotating collector, all of which are inexpensive and straightforward to operate. The demonstration that this setup can accommodate inorganic loadings up to 30 percent by weight—while still yielding self-supported mats with sub-200-nanometer fibers—suggests that the technique’s real bottleneck is not fiber formation itself but the rheology and homogeneity of the precursor solutions.

For applications, the combination of hydrophobic surfaces, interconnected porosity, and tunable stiffness is particularly relevant to membrane-based separations, where water-repellent fibrous mats are sought for treatments involving oily wastewater or for supporting catalytic and adsorptive phases. The observation that a simple water-ethanol test liquid lowers contact angles hints at how wetting behavior could be tuned in practice, either through liquid choice or through post-processing that modifies surface texture. The authors’ open-access publication, released in the first volume of the Journal of Materials Science: Polymers, makes the full dataset available to groups working on scalable nanocomposite fibers, and the identification of agglomeration as the dominant failure mode above roughly 10 percent clay gives a clear target for subsequent studies employing surface-modified or organophilic clays, alternative solvents, or in-line dispersion methods.

Subject of Research: Fabrication of hydrophobic PVDF/clay fibrous nanocomposites via solution blow spinning with tunable mechanical properties

Article Title: Hydrophobic PVDF/clay fibrous nanocomposites prepared by solution blow spinning with tunable mechanical properties

Article References: Dias, G. D. C., Zadorosny, L., Sanches, A. O., de Paula, F. R., dos Santos, M. C., & Malmonge, L. F. (2026). Hydrophobic PVDF/clay fibrous nanocomposites prepared by solution blow spinning with tunable mechanical properties. Journal of Materials Science: Polymers, 1(1), Article 19. https://doi.org/10.1007/s44493-026-00018-1

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00018-1

Keywords: PVDF, montmorillonite clay, solution blow spinning, nanocomposites, nanofibers, hydrophobicity, contact angle, tensile properties, thermal stability, crystalline phases, fibrous membranes, morphology