Nanoparticles: Hope for the agriculture of the future
Young geochemist Martin Šebesta from the Faculty of Natural Sciences became the 2023 Personality in science and technology under 35. A jury of experts recognised his research of inorganic nanoparticles. The young researcher studies how these small particles work in soil, water and on plants. He is also looking for ways to increase the positive effects of zinc nanoparticles on plants.
How can you describe a nanoparticle?
A nanoparticle can only be seen under an electron microscope, nanoparticles measure from 1 to 100 nanometres. For comparison, the diameter of a hair is 40 to 100 micrometres and 1 micrometre is 1000 nanometres. So the diameter of a hair is equivalent to between 40,000 and 100,000 nanoparticles.
What is it like to work with something that small in the lab? How do you research them?
We work with very large numbers and observe them as white or coloured powder, which is actually just a big bunch of nanoparticles. When we "dissolve" them in water, they form a very fine, cloudy mixture of some colour, depending on what substance they contain. I really enjoy showing our students nanoparticles of gold. They measure about 14 nanometres and their suspension looks like a ferociously purple soft drink.
But we all know that gold is yellow.
That is precisely what happens on nano-scale. Nanoparticles are very tiny and exhibit special quantum effects, which means they produce a different colour than micro- or macro- particles. This comes from physics that I personally do not research, just make use of. We can measure how many nanoparticles there are in, say, a litre of solution. It is similar to dissolving soluble chemicals, except nanoparticles are not really soluble at all. They are just so small and have such a large surface charge that they repel each other. Because of this property, they can pretend to dissolve, i.e. become suspended.
In your research, you study the concentration of nanoparticles in the soil, determining when their concentration becomes harmful and when it has positive effects on the soil. How did you get there?
During my master study, I researched how the pharmaceutical substance ibuprofen binds to soil. It gets there, for example, from sewage sludge. Ibuprofen is a small, simple molecule, so it is usually very easily consumed by microorganisms as a source of carbon. I came across studies on nanoparticles of ibuprofen that can increase its effectiveness in the human body. And since I was already working with soil samples, I began focusing on inorganic nanoparticles in soil during my doctoral studies.
You research man-made inorganic nanoparticles. What kind are they?
I mostly focus on zinc, or more exactly, zinc oxide nanoparticles. Zinc is one of the important micronutrients for plants. It is essential as a coenzyme in more than 200 enzymes, to maintain correct chemical reactions in the body. However, plants suffer from a lack of zinc in areas with strong soil weathering, i.e. in the tropical and subtropical zones. Zinc oxide is quickly leached from the soil.
Can that be prevented?
That is precisely our focus right now. We investigate how zinc oxide nanoparticles of different sizes behave in soil. We discovered that it is more effective to add zinc to the surface of the leaves than to add it into the soil. Nanoparticles remain on the leaf surface and form a kind of film. They quickly reach the parts of the leaf that are important for photosynthesis. At the same time, they slightly absorb or reflect UVA and UVB radiation. In this way they protect photosynthetic pigments such as chlorophyll. This increases the lifespan of the pigments and prevents them from degrading as quickly in sunlight. The effect is similar to that of sunscreen on the skin. There, you also create a film of mineral sunscreen that reflects UVA and UVB radiation. Nanoparticles can be transparent, but they still capture UVA and UVB rays.
Does that mean that spraying zinc compounds on plants in the form of nanoparticles could have a great effect on the overall prosperity of the plant?
Yes, and it could significantly help agriculture in dry and hot climates. Given overall climate developments, this is starting to be a problem in our country as well.
| Mgr. Martin Šebesta, PhD., | ||
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In your VEGA project, you also study inorganic nanoparticles and fungi. How are they related?
We are studying how to "wrap" a nanoparticle of, for example, zinc oxide so that as much zinc as possible reaches the plant exactly where it is needed. Wood-decay fungi like the oyster mushroom are special in that they want to penetrate the tissues of the plant, and have specific enzymes to do that. These enzymes could also help the nanoparticle get into the plant better. In other words, we want to use the properties of mushrooms and moulds that we usually don't particularly like, for something useful. We synthesize nanoparticles in the presence of organic substances secreted by the fungi, and we investigate how they are transported to the inner tissues, where in the plant they accumulate, and so on.
Where do you source the mushrooms for your research?
My doctoral student Veronika Cyprichová has a mushroom farm run by the non-profit organization Drž hubu (Literal Slovak translation: 'Hold the Mushroom’, and also ‘Shut Up!’). Only the fruit body of the mushroom can be sold for consumption, but the most vital part – the mycelium that spreads through the soil or dying tree trunks – is usually thrown away and composted. However, this is the part of the fungus from which we can obtain various enzymes and proteins by extracting them into a solution. And that is the ‘wrapper’ for our nanoparticles. The coated nanoparticles could theoretically have similar or even better properties than uncoated ones. It is also a very "green" procedure, because we use the natural properties of mushrooms and work with something that would otherwise be discarded as waste.
So the plant fertilizer of the future could be a combination of zinc nanoparticles and their coating, made of proteins from organic matter that would otherwise end up as waste, applied by spraying on leaves.
Yes. I believe that the ultimate goal of this research is to produce commercially viable nanoparticles with a coating that is well absorbed and utilised by the plant.
Where will your research lead you next?
In the following years, I will synthesize other metals: in addition to zinc oxide nanoparticles we also want to work with iron, because iron is another important element for living organisms. But I also work with gold. Of course, gold nanoparticles will not be applied commercially to plants because even if they had any positive effect, the cost would be too great. But gold is a very good subject for analysis, because it is easy to work with. We can easily see whether its nanoparticles penetrated into certain parts of the leaves or stem. At the same time, we know that all the gold we measure in the plant is the gold that we applied to it and the plant did not obtain it from other sources like soil. With zinc, this is impossible to guarantee, because the plant must have already contained a certain amount of zinc before the experiment, or else it would not have grown at all.
You have received the Slovak 2023 Personality in science and technology under 35 prize. The award was presented to you at the gala dinner which was the culmination of the Week of Science and Technology. What does that mean for you?
In a way, it was very pleasant. The only stressful thing was that this was my first time speaking on live TV. I think I can give a lecture, I can be quite confident in front of the class, but with three spotlights in my face on stage, it was much more difficult. I did have a prepared speech, but the moment I walked on the stage, I forgot all of it.
In addition to lecturing at the faculty, you are also an avid populariser of science.
I was a lecturer for the non-profit environmental organization Daphne, which educates students about environmental protection. I gave lectures at primary and secondary schools and gave tours to groups of children of places of exceptional natural interest or preserved natural areas around Bratislava – Dunajské luhy or Devínska kobyla, which supports enormous biodiversity, many rare species and unusual habitats. Through Daphne, as a college student, I went to the U.S. for 10 months, to one of the most popular national parks, the Cuyahoga Valley National Park in Ohio. In the environmental education center there, I lectured to primary and secondary school children about the environment. I'm still learning to talk about my own research in an intelligible way, and I realise it is very important.
How does the Faculty of Natural Sciences support your research?
Our laboratory was renovated using ACCORD project funding, we now have better equipment and the overall work environment was greatly improved. We also have a good cooperation with the Slovak Academy of Sciences, who can do analyses for us which we are unable to do with our equipment. I also have great team-mates, and the head of our Institute for Laboratory Research of Geomaterials, associate professor Peter Matúš, gives me sufficient freedom in research.
Barbora Tancerová