Dual emission carbon dots strengthen maize photosynthesis and stress tolerance by converting light more efficiently and reducing oxidative damage, offering a new approach to crop resilience in saline soils.
(Nanowerk Spotlight) Salty soils are becoming one of agriculture’s most persistent constraints. As irrigation water evaporates and leaves minerals behind, salt concentrations rise to levels that can halt plant growth entirely. About a fifth of irrigated farmland worldwide is now affected, and the problem is intensifying as drought and intensive farming alter the global water cycle. Salinity reduces a plant’s ability to absorb water, disrupts nutrient balance, and triggers the production of reactive oxygen species, chemically aggressive forms of oxygen that damage cells from within.
Managing these effects has proved difficult. Breeding can only extend salt tolerance so far before yield declines, and chemical treatments often create new environmental burdens. At the same time, photosynthesis itself operates well below its theoretical limit. Chloroplasts absorb only certain bands of light, leaving much of the available solar energy unused. A material that could both relieve oxidative stress and improve light use would address two major physiological barriers to crop performance.
That goal has drawn researchers toward nanomaterials. Metal oxide nanoparticles can catalyze reactions that limit oxidative damage, but their toxicity and stability remain unresolved. Carbon-based nanomaterials, which consist mainly of inert carbon and can be modified easily, provide a more biocompatible alternative.
Among these, carbon dots stand out for their strong light emission, chemical stability, and small size. These spherical particles measure only a few nanometers across and can pass into plant tissues without disrupting growth. Earlier experiments showed that carbon dots can enhance photosynthesis or neutralize reactive oxygen species, but rarely both. Combining those functions in one material has remained a technical gap.
The design aligns the dots’ optical output with the absorption peaks of chlorophyll, the pigment responsible for photosynthesis, while providing antioxidant protection under salt stress. The researchers test this system in maize, tracking effects on chloroplast activity, growth, and gene expression.
Proposed experimental design. a) Microwave-assisted synthesis dual-emission carbon dot (CD) nanozymes from glutathione/formamide precursors. b) Photosynthetic enhancement via spectral-matched fluorescence and electron transport facilitation in chloroplasts. c) Salt stressmitigation of corn seeds through SOD-like activity. d) Synergetic growth promotion in saline soils through photonic and antioxidant functions of CD nanozymes. (Image: Reprinted from DOI:10.1002/advs.202506906, CC BY) (click on image to enlarge)
The carbon dots were synthesized by heating glutathione and formamide in a microwave reactor, a rapid and inexpensive method that yields uniform particles. Each dot measured roughly four nanometers in diameter and contained a graphitic carbon core surrounded by surface groups rich in oxygen, nitrogen, and sulfur.
Spectroscopic analysis identified carboxyl, hydroxyl, carbonyl, and amino groups on the surface. These groups determine how the dots interact with light and with reactive molecules inside plant cells.
When illuminated, the material emitted both blue light around 466 nanometers and red light near 683 nanometers. The blue emission originated from the carbon core, while the red emission depended on carbonyl groups on the surface. Those wavelengths match the main absorption bands of chlorophyll. When the carbonyl groups were chemically reduced, the red emission nearly disappeared, confirming their central role.
This dual emission means that the dots can absorb higher-energy light and convert it into wavelengths that chloroplasts can use for photosynthesis.
To test this, the team isolated chloroplasts from maize leaves and used the Hill reaction, a standard assay that measures the efficiency of electron transfer in the light reactions of photosynthesis. Chloroplasts mixed with the carbon dots transferred electrons more quickly than chloroplasts alone, indicating enhanced photochemical activity. Photoelectrochemical measurements showed a stronger light-driven current when carbon dots were present, suggesting that they improve both light absorption and charge transport.
The same material was then tested in living plants. In hydroponic maize seedlings, a seven-day treatment with ten milligrams per liter of carbon dots increased shoot length by nearly 28 percent, root length by about 12 percent, and total biomass by around 30 percent. Chlorophyll content rose by more than 14 percent, and measurements of gas exchange showed higher photosynthetic rate, stomatal conductance, transpiration, and water-use efficiency. Imaging confirmed that the particles moved through the roots into stems and leaves and accumulated near chloroplasts, where they could directly influence light capture.
Salt stress presented the more demanding test. Under high salinity, plants accumulate reactive oxygen species that cause oxidative damage. The carbon dots displayed superoxide dismutase-like activity, mimicking an enzyme that converts superoxide radicals into less reactive forms of oxygen.
In chemical assays, increasing the concentration of carbon dots reduced superoxide levels, with about 38 percent removal at a moderate dose. Tests that modified surface chemistry showed that carbonyl and hydroxyl groups were essential to this activity.
Seed germination experiments demonstrated how this property translates into physiological protection. Corn seeds exposed to salt alone germinated at roughly half their normal rate. Seeds pretreated with carbon dots reached an 86 percent germination rate under the same conditions. The seedlings grew longer shoots and roots, contained more chlorophyll, and showed lower levels of oxidative damage markers such as malondialdehyde.
After two weeks under saline conditions, the treated plants continued to outperform untreated controls, maintaining higher growth rates and photosynthetic efficiency.
In young seedlings already growing under salt stress, foliar applications of carbon dots helped sustain development. Treated plants maintained nearly normal leaf structure and photosynthetic function, while untreated ones showed characteristic salt damage such as chloroplast distortion and reduced pigment content.
Pot experiments under more realistic soil conditions confirmed the results. When maize plants were grown in saline soil treated with carbon dots, their fresh weight increased by more than half and their dry weight by almost sixty percent compared with salt-stressed controls. Shoot and root lengths improved by about a third. Measurements of photosynthetic parameters revealed large gains.
Net photosynthetic rate rose by sixty-three percent, stomatal conductance by thirty-four percent, and photosystem II efficiency by nearly ten percent. These changes indicate that the material helped plants maintain both structural growth and photochemical activity under stress.
Chemical analyses of treated leaves showed parallel improvements. Reactive oxygen species decreased, while chlorophyll, vitamin C, and polyphenols increased. These compounds are natural antioxidants, suggesting that the carbon dots not only scavenge harmful molecules directly but also stimulate the plant’s own defense pathways. Nitrate and soluble sugar levels rose, supporting osmotic balance and energy metabolism. Root activity increased by more than sixty percent, a sign of restored physiological vigor.
To explore how the treatment affected gene regulation, the team sequenced messenger RNA from leaves of salt-stressed plants with and without carbon dots. They identified more than fifteen hundred genes whose activity changed significantly. Many were linked to energy metabolism, amino acid synthesis, and the production of secondary metabolites. Genes that drive ATP generation, such as pyruvate kinase and glyceraldehyde 3-phosphate dehydrogenase, showed strong upregulation.
Enzymes involved in nitrogen recycling, including glutamine synthase and glutamate synthase, also increased in activity. Genes associated with the synthesis of antioxidant compounds were elevated, indicating a coordinated adjustment of metabolism that supports both growth and stress tolerance.
Together, the findings outline a coherent mechanism. The carbon dots sit close to chloroplasts and convert incoming light into wavelengths that chlorophyll absorbs efficiently, which strengthens the light reactions of photosynthesis. Their surface groups remove harmful oxygen species and reduce the burden of oxidative stress. The result is a plant that captures light more effectively and maintains metabolic stability under salt exposure. The synthesis process is fast, low cost, and relies on common reagents, which suggests that similar materials could be tailored for other crops.
The work stands out because it integrates optical and enzymatic functions in one simple, biocompatible nanomaterial. The study demonstrates consistent results across laboratory assays, hydroponic systems, and soil experiments. It also highlights a design principle for future research: aligning the emission spectrum of carbon-based particles with chloroplast absorption bands while maintaining active surface chemistry that neutralizes reactive oxygen species.
Field-scale testing, environmental assessment, and cost evaluation remain necessary before practical use, but the results published in Advanced Science show that dual-emission carbon dot nanozymes can strengthen photosynthesis and stress tolerance in maize under saline conditions.
This approach connects materials chemistry with plant physiology in a direct and testable way, pointing toward new tools for sustaining crops in challenging environments.
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