Chitosan Nanoparticles Boost Selenium and Iodine Uptake in Spinach Across Three Seasons

Selenium and iodine are two of the most widespread micronutrient deficiencies on the planet, quietly shaping the health of billions of people who never realize their diets lack these essential trace elements. Now, a team of researchers from Polish universities, working with a collaborator in Malaysia, has reported the first field-based, three-season evidence that a nanotechnology approach can dramatically improve the way these nutrients are delivered into one of the world’s most popular leafy vegetables. Their study, published in Applied Microbiology and Biotechnology, shows that wrapping selenium and iodine in chitosan nanoparticles and spraying the formulation onto spinach leaves boosts fertilization efficiency by roughly 41 percent for selenium and 34 percent for iodine compared with conventional ionic salt fertilizers. The work, led by Ewelina Grochowska of the University of Agriculture in Kraków together with corresponding author Anna Gorczyca, offers a promising route toward functional foods that could help close global micronutrient gaps without requiring people to change what they eat.

The strategy the researchers tested is known as agronomic biofortification, which involves enriching crops with trace elements during cultivation rather than relying on genetic modification or dietary supplements. Conventional biofortification typically applies selenium as selenate and iodine as iodide, either to the soil or directly onto foliage. The problem is that these ionic forms are notoriously inefficient. Iodide applied to soil leaches away quickly, volatilizes into the atmosphere, or gets locked up by soil minerals before roots can absorb it. Selenate competes with sulfate for uptake channels and can be lost through runoff. Foliar sprays improve retention, but the nutrients still sit vulnerably on the leaf surface, exposed to washing off in rain, photodegradation, and inconsistent penetration through the waxy cuticle. The result is inconsistent enrichment from one field, season, or even one application to the next, which makes it difficult to guarantee that a serving of spinach will actually deliver the promised dose of micronutrients.

Chitosan nanoparticles offer a way around these limitations. Chitosan is a biopolymer derived from chitin, the structural material found in crustacean shells, and it is biodegradable, biocompatible, and naturally antimicrobial. When engineered into nanoparticles, chitosan can complex with trace elements and act as a microscopic delivery vehicle. The positively charged amino groups on chitosan bind anions such as selenate and iodide, holding them in a stable reservoir that adheres well to leaf surfaces. Because the particles are nanoscale, they can navigate the stomata and cuticular pathways of leaves far more effectively than dissolved ions alone, promoting gradual uptake rather than rapid loss. The researchers hypothesized that this controlled-release behavior would not only raise the concentration of selenium and iodine in spinach leaves but also stabilize yields when growing conditions turn hostile, since chitosan itself is known to elicit plant defense responses and mild biostimulant effects.

To test this rigorously, the team conducted a field experiment using spinach cultivar Pawnie F1, laid out in a randomized complete block design, the gold standard for agricultural trials because it controls for spatial variation in soil and microclimate. Crucially, they repeated the experiment across three distinct growing seasons in 2025 on the North European Plain: spring, summer, and autumn. This multi-season design matters enormously, because most biofortification studies are conducted in a single season or in greenhouses, leaving open the question of whether results hold up under real-world variability. The comparison pitted conventional selenate and iodide salts against the same nutrients complexed with chitosan nanoparticles, applied as foliar treatments, with the dual selenium-iodine nanoparticle formulation as the centerpiece of the study.

The yield data told a story of seasonal stress and nanoscale resilience. Fresh biomass was highest in spring, reaching 1.62 kilograms per square meter, and lowest in summer, dropping to 1.17 kilograms per square meter, reflecting the heat and light stress that spinach, a cool-season crop, experiences in midsummer. What caught the researchers’ attention was what happened in the less favorable summer and autumn seasons: plots treated with chitosan nanoparticle formulations maintained more stable yields than those treated with ionic salts. This buffering effect suggests that the nanoparticles act not merely as passive nutrient carriers but as biostimulants, helping plants cope with suboptimal conditions. For farmers, this dual benefit, enrichment plus yield stability, could make nanoparticle biofortification economically attractive even before accounting for the reduced fertilizer inputs that higher efficiency implies.

On the enrichment side, both the conventional and nanoparticle treatments significantly increased selenium and iodine concentrations in spinach leaves, confirming that foliar biofortification works in principle. But the efficiency gap was decisive. Averaged across the three seasons, the chitosan-based formulations increased fertilization efficiency for selenium by approximately 41 percent and for iodine by approximately 34 percent relative to the ionic salt formulations. In practical terms, this means farmers could achieve the same nutritional enrichment with substantially less applied nutrient, reducing costs and minimizing the environmental losses that plague conventional fertilization. Importantly, applying selenium and iodine together via the nanoparticles did not reduce the uptake efficiency of either element, demonstrating that simultaneous dual biofortification is technically feasible, something that has been difficult to guarantee with ionic forms because of potential chemical interactions between the two trace elements.

To make sense of the complex dataset, the researchers employed principal component analysis, a statistical technique that condenses many correlated measurements into a few underlying axes of variation. The first principal component, accounting for 36.5 percent of the variability, was dominated by growing season, confirming that weather and photoperiod were the largest sources of variation in the experiment. The second component, explaining 27.5 percent, captured the biofortification effect itself. Within this statistical landscape, the chitosan nanoparticle treatments formed a distinct cluster associated with both higher yields and higher nutrient content, visually separating them from the ionic treatments and reinforcing the conclusion that the nanocarrier fundamentally changes how the crop responds to fertilization.

Food safety, of course, is the make-or-break question for any biofortification technology, and the study addressed it head-on. Spinach is a notorious accumulator of nitrates, which can be converted to nitrites and pose health risks, particularly for infants. The researchers measured nitrate and nitrite levels in the enriched leaves and found that all values remained within the limits set by European Union regulations, regardless of treatment. They then calculated the maximum single-day intake, or MSDI, of selenium and iodine for different consumer groups and confirmed that even the most enriched spinach was safe for all age groups, from children to adults. This dual safety verification, covering both antinutritional compounds and trace element intake, provides the evidence base regulators will need before nanoparticle-fortified crops can reach the market.

The implications stretch well beyond spinach. Micronutrient deficiency, sometimes called hidden hunger, affects an estimated two billion people worldwide, and staple-crop biofortification programs have made progress but often struggle with the same uptake inefficiencies that motivated this study. A biodegradable, shell-derived nanocarrier that boosts efficiency by a third or more while stabilizing yields under stress could be adapted to other leafy vegetables and trace elements, potentially transforming functional food production. The work was supported by Poland’s Implementation Doctorate 2024 program funded by the Ministry of Science and Higher Education, reflecting a deliberate push to move nanotechnology from the laboratory into agricultural practice. As the authors note, this is the first field-based, three-season evidence supporting chitosan nanoparticles for simultaneous selenium and iodine biofortification, and it arrives at a moment when climate volatility is making every advantage in crop resilience and nutrient delivery count. If follow-up studies in other regions and crops replicate these gains, the humble spinach leaf could become a far more powerful vehicle for public health than anyone imagined a decade ago.

Subject of Research: Chitosan nanoparticle-based foliar delivery of selenium and iodine for agronomic biofortification of spinach

Article Title: Nano-delivery of selenium and iodine improves spinach biofortification

Article References: Grochowska, E., Niemiec, M., Komorowska, M., Kula-Maximenko, M., Tan, S. H., Radwan-Pragłowska, J., Mirowski, K., & Gorczyca, A. (2026). Nano-delivery of selenium and iodine improves spinach biofortification. Applied Microbiology and Biotechnology. https://doi.org/10.1007/s00253-026-14073-9

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14073-9

Keywords: chitosan nanoparticles, selenium, iodine, spinach, biofortification, foliar fertilization, micronutrient deficiency, functional food, nanobiotechnology, food safety, crop yield, plant biostimulants