The latest nanotechnology advances for agriculture

(Nanowerk Spotlight) Materials behave in unconventional ways at the nanoscale, and by combining knowledge of biology, chemistry, and nanotechnology, we can achieve the unimaginable.
Nanotechnology has the potential to revolutionize agriculture and food systems. Our agricultural system has been facing many challenges with the growing population and the adverse effects of climate change.
As a result of the rise in the global mean temperature, the weather conditions have become more unpredictable and intense. These unfavorable weather conditions are devastating for farmers. The demand for food production is increasing rapidly, and the current production rate will not be enough to satisfy the growing demand. Scientists have turned to nanotechnology to enhance food production.
Nanobiosensors, nanofertilizers, and nanopesticides have the potential to significantly change the agricultural world.
Nanotechnology research related to agriculture is still in its early stages, meaning these new products are not ready to be put on shelves. Although many of these products have shown promising results by enhancing plant growth, the nanoparticles pose a threat to humans and the environment.
The toxicity of nanoparticles is a serious concern because it can affect the plants, the soil, and the farmers. Also, the issue of chemical translocation from one plant to another is still being addressed. If a chemical reaches a non-target plant, it can have dangerous effects on it.
Overall, nanotechnology in agriculture is a promising technological advancement that can upgrade our food production, but the technology must be thoroughly researched before being implemented.

Food Production Challenges

The world is tragically facing many environmental problems which are jeopardizing our food security. The climate has been drastically changing due to the increase in levels of greenhouse gases in the atmosphere. A global mean temperature rise of 2 °C is inevitable and is likely to change environmental conditions. As the sea level rises from glaciers melting, low-lying croplands will be submerged, and river systems will experience more extreme seasonal flows as well as flooding.
Also, the increase in global temperatures will change rainfall patterns. Areas like Africa and South Asia that heavily rely on rainfed agriculture will have shorter growing seasons1). The warmer temperatures result in more droughts, floods, heatwaves, frosts, and other extreme weather conditions. The variability of the weather will increase as well. Agriculture is sensitive to weather conditions, so these climatic changes are challenging our food security.
The freshwater shortage is also a serious concern. Many rivers don’t reach the ocean, and about 50% of the world’s wetlands have disappeared. The amount of fresh water available per person has decreased fourfold in the past 60 years2).
In addition to climate change, the global population is expected to increase from 6.7 billion to 9 billion by 20502). The world agricultural output needs to rise by 50% by 2030 to keep up with this rising population3).
It is difficult to meet the high food demands because a large amount of the arable land is lost to urbanization, salinization, desertification, and degradation. The world is struggling to feed the growing population with unpredictable weather, shrinking landscape, and water shortage. To cope with these challenges, innovative technology such as nanotechnology is needed to make our food production more reliable.

Nanobiosensors

Nanosensors are devices that respond to small changes in the environment and convert them into useful forms of information. Nanobiosensors combine knowledge of biology, chemistry, and nanotechnology to improve crop productivity. They are used to detect chemical species such as microbes, contaminants, pollutants, and food freshness and monitor environmental conditions4).
Nano smart dust and gas sensors will make it possible to evaluate the presence of pollutants in the environment5). Typically, these devices are used to detect food spoilage in storage, packaging, and transport. Compared to traditional sensors, nanosensors have a higher sensitivity and selectivity, near real-time detections, low cost, and portability6).
Nanosensors have a similar structure to ordinary sensors, except they are produced at nanoscale. Because of their size, nanosensors can be attached to nearly anything and send signals. These tiny sensors are capable of detecting and responding to physicochemical and biological signals and transferring that response into an output. There are many ways to develop nanosensors like top-down lithography, molecular self-assembly, and bottom-up assembly6).
The application of nanomaterials such as metal gold, silver, cobalt, nanoparticles, carbon nanotubes, magnetic nanoparticles, and quantum dots in nanobiosensors are still being studied7). The high specificity of biosensors is due to the combination of bioreceptors with an acceptable transducer which produces a signal when the target molecule is present6).
Biosensors made of electrochemically functionalized SWCNTs fabricated with either metal nanoparticles (NPs) or metal oxide nanoparticles, and metal oxide nanowires and nanotubes can be used to detect gases like ammonia, nitrogen oxide, hydrogen sulfide, sulfur dioxide, and volatile organics8). This function makes the biosensors a favorable device for monitoring agricultural pollutants. With nanobiosensors in use, farmers will be able to understand their crops better and make better decisions because they can monitor the condition of their crops.
Dr. S. Neethirajan developed a tiny sensor using microelectronics and nanotechnology to help farmers detect early signs of grain spoilage during storage6). The sensor is the size of a dime and can detect parts per billion levels of carbon dioxide and odor-causing chemicals to find the cause and source of the spoilage.
Different insects and fungi can grow in grain and each one releases a different chemical which can be detected by the sensors. Once the insect or fungus is detected, a treatment is distributed to solve the problem. The team of researchers is working towards making these nanosensors wireless, so multiple sensors can be distributed throughout the grain to accurately locate and assess the source of spoilage6).
Although nanosensors have many advantages, some setbacks are keeping them from being fully implemented into agricultural production. The environmental health and safety (EHS) of nanotechnology-enabled products must be evaluated because these devices come into contact with humans and the environment.
More specifically, the toxicity of these sensors must be studied to minimize the potential harm the sensors may bring to humans, as well as the environmental exposure from the pre-use and post-use lifecycle. Studies have been conducted on animals to investigate the potential toxicity of nanomaterials for the liver, kidneys, and immune system6).
The concern over safety for nano-products is far greater than for non-nano products because the analytical methods and procedures to acquire and evaluate safety-related information for nanomaterials are still under development. It is difficult to take safety precautions into account when designing nanomaterials because of the knowledge gap related to toxicity and exposure. This drawback is delaying the full implementation of nanosensors.

Nanofertilizers

Nanofertilizers are nanomaterials that provide nutrients to plants to enhance their growth and health. Using nanofertilizers instead of traditional fertilizers allows the nutrients to be released into the soil in a gradual and controlled way, preventing the pollution of water resources.
The advantages of nanofertilizers include increased efficiency of their constituents, lower soil toxicity, and a reduced frequency of fertilizer application. Maize treated with nanoparticles of titanium oxide (TiO2) showed improvements in growth, whereas maize treated with TiO2 in bulk had no significant changes8). Another example is soybeans treated with silicon oxide (SiO2) and TiO2 nanoparticles to improve the activity of nitrate reductase and increase plant absorption capacity.
There are three types of nutrients delivered by nanofertilizers: macronutrients, micronutrients, and nanoparticulates. Macronutrients are needed in large quantities, and they are vital for plant growth. Many researchers have developed macronutrient nanofertilizers and have used them at laboratory and field scales.
The macronutrient fertilizer requirement will increase as the demand for food production increases. The fertilizer requirement will be up to 263 MT by 20509). Nitrogen, phosphorus, potassium, magnesium, sulfur, and calcium are important macronutrients for plant growth10). The high-volume-to-surface ratio of macronutrient nanofertilizers reduces the amount needed and increases the efficiency compared to traditional fertilizers.
R. Liu and R. Lal synthesized a calcium nanoparticle to replace conventional calcium macronutrients, and they measured a 15% increase in biomass of Arachis hypogaea9). Macronutrient nanofertilizers have proven to enhance plant growth. Moreover, micronutrients are required in small quantities and are essential for plant metabolic processes. The bioavailability of micronutrients, nutrition quality, and plant growth are improved when they are in nanoform. Zinc is an essential micronutrient because it regulates the different enzymatic activities in plants.
In a study of N. Alexandratos N and J. Bruinsma, the effects of zinc oxide (ZnO) nanoparticles were tested in Vigna radiate, Cicer ariatium, Cucumis sativas, Raphanus sativus, Brassica napus, and Cluster bean9). The results showed improvement in biomass, shoot length, root, chlorophyll and protein content, and phosphatase enzyme activity. Similarly, spraying 0.05 ppm concentrated manganese (Mn) nanoparticles on Vigna radiata increased the root length by 52%, shoot length by 38%, and biomass by 38% compared to bulk Manganese sulfate (MnSO4). Lastly, nanoparticulates, also known as nutrient-loaded nanofertilizers, are necessary for plant growth promoter activities.
TiO2, SiO2, and carbon nanotubes (CNTs) are commonly used as nanoparticulate fertilizers. CNTs as fertilizers are anticipated to promote water intake capacity and plant growth by entering the germinating seeds. In a study, multiwalled carbon nanotubes (MWCNTs) showed a 55-64% increase in the growth of tobacco cell culture compared to the control group11). All three types of nano-nutrients are necessary for efficient and healthy plant growth.
It is critical to consider the limitations of nanofertilizers before mass implementation. Nanomaterials are very reactive as a result of their small size and enhanced surface area. The plant phytotoxicity from nanomaterials is an issue because different plants respond in various ways to nanomaterials in a volume-dependent manner12).
Nanofertilizers can be absorbed through roots or leaves and translocated to different plants. The unwanted uptake of nanofertilizers by the wrong plant can not only negatively affect the physiology of the plant, but can also be toxic to humans. For this reason, it is crucial to further investigate the safety of nanofertilizers before using them in agricultural fields.

Nanopesticides

Insect pests are a predominant issue in the agricultural field, making nanopesticides a key player in controlling insect pests and host pathogens. Recently, a nanoencapsulated pesticide formulation was developed. This type of pesticide has slow releasing properties with enhanced solubility, specificity, permeability, and stability7). The properties of the nanopesticide are kept intact by protecting the active ingredients in the capsule from premature degradation or by enhancing their pest control efficacy for a longer period.
The main goal of nanopesticide development is to increase the solubility of poorly soluble active ingredients. One way to achieve this is through nanoemulsions which are formed by the emulsion of nanoscale droplets. Due to the size of the droplets, the high ratio of surface area to volume, and elastic modulus, nanoemulsions are far more than regular emulsions7).
Additionally, nanoemulsions contain a lower concentration of surfactants than microemulsions. Typically, nanoemulsions contain 5-10% of surfactant, while microemulsions contain about 20%13). Nanoemulsions can be produced by methods requiring a high energy input, which makes it difficult to scale up for commercial agrochemical production.
Recent research has developed more practical, low energy methods such as spontaneous emulsification and phase inversion temperature methods, but the precise mechanisms of these methods are still under research13).
In a study, the effect of nanopesticide based on copper hydroxide (Cu(OH)2) on lettuce leaves was evaluated. After a series of tests, the leaves had no visible damage, and in some instances, the biomass of the leaves increased significantly. The Cu(OH)2 nanopesticide entered through the stomata and remained mainly in the leaves. Some of the copper (Cu) translocated to the roots.
The results also revealed that the metabolite levels of the leaves were disturbed, however, more research is necessary to determine if the cause of the disturbance was from the Cu or the nanoparticles14).
Overall, the development, efficacy, and effects of nanopesticides must be researched more closely before implementing them in agricultural fields.

Conclusion

In particular, the extensive release of nanomaterials into the environment and the food chain may pose a risk to human health. In conclusion, although nanofertilizers used in agriculture are offering great opportunities to improve plant nutrition and stress tolerance to achieve higher yields in a frame of climate change, not all nanomaterials will be equally safe for all applications. The risks of nanofertilizers and nanopesticides should be thoroughly examined before use, and further biotechnological advances are required for a correct and safe application of nanomaterials in agriculture.

References

[1] John R. Beddington, Mohammed Asaduzzaman, Fernandez A. Bremauntz, Megan E. Clark, Marion Guillou, et al. Achieving food security in the face of climate change: final report from the Commission on Sustainable Agriculture and Climate Change. 2012. https://bit.ly/3uehLO4
[2] Ronald, Pamela. “Plant Genetics, Sustainable Agriculture and Global Food Security.” Genetics, 1 May 2011, doi: 10.1534/genetics.111.128553 .
[3] Baulcombe, D., Crute, I., Davies, B., Dunwell, J., Gale , M., Jones, J., Pretty, J., Sutherland, W. and Toulmin, C., (2009) Reaping the benefits: science and the sustainable intensification of global agriculture. Report. The Royal Society pp72. ISBN 9780854037841
[4] Joyner, J.R., Kumar, D.V. (2015). Nanosensors and their applications in food analysis: a review, The International Journal of Science & Technoledge, Vol. 13, Issue 4, 80-90
[5] Mousavi, Sayed Roholla, and Maryam Rezaei. “Nanotechnology in Agriculture and Food Production.” Journal of Applied Environmental and Biological Sciences, 2011.
[6] Mikličanin, Enisa Omanović, and Mirjana Maksimović. “Nanosensors Applications in Agriculture and Food Industry.” Bulletin of the Chemists and Technologists of Bosnia and Herzegovina, 2016.
[7] Prasad, Ram et al. “Nanotechnology in Sustainable Agriculture: Recent Developments, Challenges, and Perspectives.” Frontiers in Microbiology Vol. 8 1014. 20 Jun. 2017, doi:10.3389/fmicb.2017.01014
[8] Sekhon, Bhupinder Singh. “Nanotechnology in agri-food production: an overview.” Nanotechnology, Science and Applications Vol. 7 31-53. 20 May. 2014, doi:10.2147/NSA.S39406
[9] Alexandratos N, Bruinsma J (2012) World agriculture towards 2030/2050, the 2012 revision. 2012, ESA Working Paper No. 12–03. FAO, Rome
[10] Chhipa, Hemraj. “Nanofertilizers and Nanopesticides for Agriculture” Environmental Chemistry Letters, 5 Dec. 2016, doi:10.1007/s10311-016-0600-4.
[11] Khodakovskaya, Mariya V., et al. “Carbon Nanotubes Induce Growth Enhancement of Tobacco Cells.” ACS Nano, Vol. 6, No. 3, 2012, pp. 2128–2135., doi:10.1021/nn204643g.
[12] Zulfiqar, Faisal, et al. “Nanofertilizer Use for Sustainable Agriculture: Advantages and Limitations.” Plant Science, Vol. 289, 2019, p. 110270., doi:10.1016/j.plantsci.2019.110270.
[13] M. Kah, S. Beulke, K. Tiede & T. Hofmann (2013) Nanopesticides: State of Knowledge, Environmental Fate, and Exposure Modeling, Critical Reviews in Environmental Science and Technology, 43:16, 1823-1867, doi:10.1080/10643389.2012.671750
[14] Zhao, Lijuan, et al. “Metabolomics to Detect Response of Lettuce (Lactuca Sativa) to Cu(OH)2 Nanopesticides: Oxidative Stress Response and Detoxification Mechanisms.” Environmental Science & Technology, Vol. 50, No. 17, 2016, pp. 9697–9707., doi:10.1021/acs.est.6b02763.
Provided by Ms. Sharika Hoque, Dr. Raj Shah, Dr. Steve Nitodas as a Nanowerk exclusive.

About the Authors

Ms. Sharika Hoque is part of a thriving internship program at Koehler Instrument company and a student of chemical engineering at State University of New York, Stony Brook, where Dr. Shah currently heads the External advisory board of directors.
Dr. Raj Shah is a Director at Koehler Instrument Company in New York, where he has worked for the last 25 years. He is an elected Fellow by his peers at IChemE, CMI, STLE, AIC, NLGI, INSTMC, The Energy Institute and The Royal Society of Chemistry An ASTM Eagle award recipient, Dr. Shah recently coedited the bestseller, Fuels and Lubricants handbook.
A Ph.D in Chemical Engineering from The Penn State University and a Fellow from The Chartered Management Institute, London, Dr. Shah is also a Chartered Scientist with the Science Council, a Chartered Petroleum Engineer with the Energy Institute and a Chartered Engineer with the Engineering council, UK. An adjunct professor at the Dept. of Material Science and Chemical Engineering at State University of New York, Stony Brook, Raj has over 375 publications and has been active in the petroleum field for 3 decades.
Dr. Steve (Stephanos) Nitodas is currently a member of the Faculty of the Department of Materials Science and Chemical Engineering at Stony Brook University, NY. His expertise lies in the synthesis and applications of nanostructured carbon and polymer nanocomposites. Dr. Nitodas has worked for several years in the nanotechnology industry, possessing significant know-how related to transfer of knowledge from academia to the industry and the setup of startup companies.

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