How helpful is nanotechnology in agriculture?

Nanoscale carriers can be utilized for the efficient delivery of fertilizers, pesticides, herbicides, plant growth regulators, etc. The mechanisms involved in the efficient delivery, better storage and controlled release include: encapsulation and entrapment, polymers and dendrimers, surface ionic and weak bond attachments among others. These mechanisms help improve stability against degradation in the environment and ultimately reduce the amount to be applied, which reduces chemical runoff and alleviates environmental problems. These carriers can be designed in such a way that they can anchor the plant roots to the surrounding soil structure and organic matter. This can only be possible through the understanding of molecular and conformational mechanisms between the delivery nanoscale structure and targeted structures and matter in soil [5]. These advances will help in slowing the uptake of active ingredients, thereby reducing the amount of inputs to be used and also the waste produced.

We are able to study the physico-chemical and biological interactions between plant cell bodies and various disease-causing organisms, i.e. pathogens, through the advancement in nanofabrication and characterization tools. These tools have helped us in understanding the mechanisms involved and ultimately improved the strategies for the treatment of these diseases [6]. For example in the past, to study xylem-inhabiting bacteria, changes in bacterial populations were monitored through destructive sampling techniques at different distances from inoculation sites but this does not provide information about colonization, film development, and subsequent movement and re-colonization at new areas because the same sample site cannot be followed temporarily. It has only been through the discovery of micro-fabricated xylem vessels with nano-sized features that we are able to study the above mechanisms which otherwise was not possible through traditional methods [7].

Recently, nanosized lignocellulosic materials have been obtained from crops and trees which had opened a new market for innovative and value-added nano-sized materials and products, e.g. nano-sized cellulosic crystals have been used as lightweight reinforcement in polymeric matrix [8, 9]. These can be applied in food and other packaging, construction, and transportation vehicle body structures. Cellulosic nano-whisker production technology from wheat straw has been developed by Michigan Biotechnology Incorporate (MBI) International, and is expected to make biocomposites that could substitute for fiberglass and plastics in many applications, including automotive parts [10]. For the commercialization of this technology, North Dakota State University (NDSU) is currently engaged in a project.

Clay nanotubes (Halloysite) have been developed as carriers of pesticides for low cost, extended release and better contact with plants, and they will reduce the amount of pesticides by 70–80%, hence reducing the cost of pesticide and also the impact on water streams [11].

One of the processes using nanoparticles is photocatalysis [12]. It is a combination of two words 'photo' means 'light' and 'catalysis' means 'reaction caused by a catalyst'. So, it involves the reaction of catalyst (nanoparticles) with chemical compounds in the presence of light. The mechanism of this reaction is that when nanoparticles of specific compounds are subjected to UV light, the electrons in the outermost shell (valence electrons) are excited resulting in the formation of electron hole pairs, i.e. negative electrons and positive holes. These are excellent oxidizing agents and include metal oxides like TiO₂ [13], ZnO [14], SnO₂ [15], etc., as well as sulfides like ZnS [16]. Due to their large surface-to-volume ratio, these have very efficient rates of degradation and disinfection (see table 2). As the size of particles decrease, surface atoms are increased, which results in tremendous increase in chemical reactivity and other physico-chemical properties related to some specific conditions such as photocatalysis, photoluminescence, etc. So this process can be used for the decomposition of many toxic compounds such as pesticides, which take a long time to degrade under normal conditions [17], e.g. pathogens, etc.

3.5.1. Bioremediation of resistant pesticides.

3.5.2. Disinfectants.

3.5.3. Wastewater treatment.

In our daily life, identification tags have been applied in wholesale agriculture and livestock products. Due to their small size, nanoparticles have been applied in many fields ranging from advanced biotechnology to agricultural encoding. Nanobarcodes (>1 million) have been applied in multiplexed bioassays and general encoding because of their possibility of formation of a large number of combinations that make them attractive for this purpose. The UV lamp and optical microscope are used for the identification of micrometer-sized glass barcodes which are formed by doping with rare earth containing a specific type of pattern of different fluorescent materials [9].

The particles to be utilized in nanobarcodes should be easily encodeable, machine-readable, durable, sub-micron-sized taggant particles. For the manufacture of these nanobarcode particles, the process is semi-automated and highly scalable, involving the electroplating of inert metals (gold, silver, etc.) into templates defining particle diameter, and then the resulting striped nanorods from the templates are released. These nanobarcodes have the following applications.

3.6.1. Biological applications of nanobarcodes.

3.6.2. Non-biological applications of nanobarcodes.

Bacteria, the most primitive life forms present almost everywhere, are useful as well as harmful for life. There are numerous bacteria which are responsible for many diseases in humans like tetanus, typhoid fever, diphtheria, syphilis, cholera, food-borne illness, leprosy and tuberculosis caused by different species. As a remedial process, we need to detect bacteria and for this, dye staining method is used. To stain bacteria, the most commonly used biolabels are organic dyes, but these are expensive and their fluorescence degrades with time. So the need of the hour is to find durable and economical alternatives.

Fluorescent labeling by quantum dots (QDs) with bio-recognition molecules has been discovered through the recent developments in the field of luminescent nanocrystals. QDs are better than conventional organic fluorophores (dyes) due to their more efficient luminescence compared to the organic dyes, narrow emission spectra, excellent photostability, symmetry and tunability according to the particle sizes and material composition. By a single excitation light source, they can be excited to all colors of the QDs due to their broad absorption spectra [23]. Bio-labeled bacillus bacteria with nanoparticle consisting of ZnS and Mn²⁺ capped with bio compatible 'chitosan' gave an orange glow when viewed under a fluorescence microscope.

For the detection of E. coli O157:H7, QDs were used as a fluorescence marker coupled with immune magnetic separation [24]. For this purpose, magnetic beads were coated with anti-E. coli O157 antibodies to selectively attach target bacteria, and biotin-conjugated anti-E. coli antibodies to form sandwich immune complexes. QDs were labeled with the immune complexes via biotin-streptavidin conjugation after magnetic separation.

A variety of characteristic volatile compounds are produced by microorganisms that are useful as well as harmful to human beings, e.g. fermentation makes use of yeasts while alcohol is produced as a by-product when bacteria eat sugar. For rapid growth of a wide range of microorganisms, dairy products, bakery products and other food products represent ideal media. The most common causal organisms of food rotting are bacteria. Foul odor is a clear indication of food rotting. The human nose can detect and distinguish a large number of odors, but sometimes it may be impractical and a further cause for poisoning. Therefore, it is more sensible to use an instrument like rapid detection biosensors for the detection of these odors.

3.8.1. Rapid detection biosensors.

3.8.2. Enzymatic biosensors.

3.8.3. Electronic nose (E-nose).

Man has been fascinated by gold for a long time. It is one of the most widely studied and abundantly used nanoparticles like bulk gold. Due to several qualities, it has remained valuable both as a medium of exchange and for decorative use as jewelry throughout history. The gold nanoparticles, commercially used as rapid testing arrays for pregnancy tests and biomolecule detectors, are based on the fact that the color of these colloids depends on the particle size, shape, refractive index of the surrounding media and separation between the nanoparticles. A quantifiable shift in the surface plasmon response (SPR) absorption peak results due to a small change in any of these parameters.

We can make these nanoparticles attach to specific molecules by carefully choosing the capping agent for stabilizing gold nanoparticles. These specific molecules get adsorbed on the surface of these nanoparticles and change the effective refractive index (RI) of the immediate surroundings of the nanoparticles [28]. A few nanoparticles will be adsorbed if the detecting molecules (bio-macromolecules) are larger than the gold nanoparticles and result in the formation of lumps after agglomeration. Ultimately, color of gold nanoparticles is changed due to shift in SPR that results from the reduction of particle spacing.

We can use the 'smart dust' technology for monitoring various parameters like temperature, humidity, and perhaps insect and disease infestation to create distributed intelligence in vineyards and orchards.

ZigBee is a wireless mesh networking standard with low-cost and utilizes low-power. It has given the concept of 'Smart Fields' and 'SoilNet'. It consists of one or more sensors for environmental data (temperature, humidity, etc.), a signal conditioning block, a microprocessor/microcontroller with an external memory chip and a radio module for wireless communication between the sensor nodes and/or a base station. It can be used for the identification and monitoring of pests, drought or increased moisture levels in order to counterbalance their adverse effects on crop production [29]. Through this wireless sensor technology with nanoscale sensitivity, we can control plant viruses and level of soil nutrients, as the plant surfaces can be changed at nanoscale with specific proteins. This technology is important in realizing the vision of smart fields in particular. Wireless network sensor technology can also be used for monitoring the optimal conditions for mobile plants biotechnology.

The main challenge in sustainable agriculture is to minimize the inputs and to maximize the output. Feedstock is the most important input in animal production. Feeding efficiency is inversely related with demand of feed, discharges of waste, environmental burden, production cost and competing with other uses of the grains, biomass and other feed materials. Nanotechnology has the potential to improve the profile of nutrients and their efficiency. In developing countries, animal feeds are mostly suboptimal in nutrient composition. To supplement them with nutrients is an efficient way of elevating the efficiency of protein synthesis and utilization of minor nutrients in animals. Similarly, cellulosic enzymes can help in better utilization of the energy in plant-derived materials. Moreover, micronutrients and bioactives can help improve the overall health of animals, ultimately achieving and maintaining optimal physiological state. For efficient supply of nutrients, a large number of nanoscale delivery systems like micelles, liposomes, nano-emulsions, biopolymeric nanoparticles, protein-carbohydrate nanoscale complexes, solid nano lipid particles, dendrimers and others have been developed. These systems not only have better adaptability against environmental stresses and processing impacts but also have high absorption and bioavailability, better solubility and disperse-ability in aqueous-based systems, i.e. food and feed, and controlled release kinetics [31]. Sustainability can be achieved through the utilization of self-assembled and thermodynamically stable structures. So less energy is needed to process these structures. In addition, efficient veterinary drug delivery can be achieved through these systems which protect the drug in gastrointestinal tract and provide optimal rate and location for optimal action. These systems have helped in improved utilization efficiency of nutrients and product quality, as well as reducing the amount and financial burden of the producers, and ultimately production yield. Similarly to food applications, it is the requirement of the system to be effective in its intended use and against adverse effects or unintended uses. There should be an accurate risk assessment of the nanoscale particles to be used in order to ensure safe and sound development and deployment in the products.

Substantial losses in animal production are caused by diseases such as bovine mastitis, tuberculosis, respiratory disease complex, Johne's disease, avian influenza, and porcine reproductive and respiratory syndrome (PRRS). According to an estimate of the World Health Organization (WHO), 1/5 of animal production costs in the developed world and 1/3 in the developing world are represented by animal diseases. During the last thirty years, infectious diseases have emerged and 75% of them are zoonotic [32], which not only cause economic loss but also serious danger to human health, e.g. Variant Creutzfeldt–Jakob disease (vCJD). The zoonotic diseases include mad cow disease, avian influenza, H1N1 influenza, Ebola virus and Nipah virus. For integrated animal disease management, detection and intervention are two important tools in order to reduce and/or to eradicate the disease. Nanotechnology has the potential to provide these strategies and has enabled revolutionary changes in this field, and new state-of-the-art strategies are expected to be developed in the near future [33, 34]. Numerous detection and diagnostic techniques have been offered by nanotechnology which are highly specific and sensitive, can detect multiple samples at a time, are time saving, robust, have on-board signal processing, communication, automation, and are convenient to use and economical. These help in quick, simple and inexpensive treatment strategies that can be taken to remedy the situation. For agricultural field applications, portable, implantable devices have been developed. Drugs and vaccines developed through nanotechnology are relatively more effective and cheaper than those manufactured through previous technologies. This has enabled precise delivery and controlled release of drugs, resulting in a small footprint in animal waste and the environment, which would otherwise result in antibiotic resistance. So it has reduced environmental concerns associated with the use of antibiotics and enabled new drug administrations that are easy, quick, non-intrusive to animals and most importantly, economical. Through advancement in nanotechnology, theragnostics has been developed in which both diagnostics and therapy are performed in a single step. But before deploying this innovative technology, pharmacokinetic and pharmacodynamic studies should be conducted under in vivo conditions in order to establish a relationship between dose, drug concentration at the site of action and drug response [35]. Moreover, there should be collaboration between human and veterinary medical communities in the research and development for dealing with zoonotic diseases.

Animal reproduction is an important challenge for both developing and developed countries, as low fertility causes low production rate, increases in financial input and reduced efficiency of livestock operations [36]. To improve animal reproduction, many technologies have been developed, but microfluidic technology has ruled over the last two decades and many nanoscale processing and monitoring technologies have been integrated, which include food and water quality, animal health and environmental contaminations. These have enabled us to produce an automated and large number of embryos in vitro, and this has improved genetics and selection of livestock for human food and fiber production. In Brazil, fixed-time artificial insemination (FTAI) technology has been used to increase the cattle reproduction rate for many years, but its efficiency depends on the regulation of progesterone. Inefficient and irregular dispersion of hormone, disposal issues, being labor intensive, and requiring multiple animal handlings for each attempt are the drawbacks of this technology. Nanotechnology-based delivery systems help to improve bioavailability and release kinetics, reduce labor intensity, and minimize waste and discharge to the environment [33, 36]. An implanted nanotechnology-enabled sensing device with wireless transmission ability is another strategy that can be used to control animal hormone level, thus providing information about the optimal available fertility period. This information is helpful for the livestock operators in decision making for reproduction [37].

Modification of animal feed not only improves the animal production but also product value and quality, which is helpful in producing animal-derived foods or products consistent with health recommendations and consumer perceptions, e.g. milk fatty acids, cis-9, trans-11 conjugated linoleic acid (CLA) and vaccenic acid (VA). These products help in the prevention of chronic human diseases such as cancer and atherogenesis [38]. Nanotechnology based delivery of nutrients is helpful in efficiently controlling the biosynthesis and concentration of CLA and VA in the milk fat of lactating ruminants. It also helps in examining the biological benefits of functional foods with high CLA/VA contents and their relationship with human chronic diseases using biomarkers and biomarker triggered release mechanisms. Moreover, it has played an important role in economical sequencing of the mammalian genome within 24 h [22]. In the next decade, if this technology is available, advances in biotechnology research and development will be substantially accelerated.

In the animal production industry, animal waste is a serious concern and its irresponsible discharge can only be prevented through strict environmental policies. It is also responsible for the production of unpleasant odors that adversely affect quality of air and, in turn, living conditions and the real estate value of the adjacent area. Animal waste could be used for the production of high-quality organic fertilizer when value is added, and for improving environmental quality. Its bioconversion into energy and electricity can result in new revenue, renewable energy in the form of natural gas [39]. In efficient and cost effective bioconversion, nanotechnology based catalysts will play a critical role in electricity production and its storage which will be very helpful in the development of distributed energy supplies, especially in rural communities where infrastructure is lacking [40,41]. Such an approach could eliminate the need for a system of wide electricity grids, accelerate rural development and improve productivity.

Physico-chemical microbial disinfection systems like chlorine dioxide, ozone and ultraviolet are being commonly used in developed countries, but most of the developing countries are lacking these systems due to the requirement of large infrastructure which makes them costly. The need of the hour is to search and develop alternative cost-effective technologies. Nanotechnology based oligodynamic metallic particles have the ability to serve this function. Among these nanomaterials, silver is the most promising one as it is both bactericidal and viricidal due to the production of reactive oxygen species (ROS) that cleaves DNA and can be utilized for a wide range of applications. Other properties include low toxicity, ease of use, its charge capacity, high surface-to-volume ratios, crystallographic structure and adaptability to various substrates [44].

Visible light photocatalysis of transition metal oxides, another nanoscale technological development, produces nanoparticles, nanoporous fibers and nanoporous foams that can be used for microbial disinfection [45] and for the removal of organic contaminants like PPCPs and EDCs. Moreover, tubular nanostructures, embedded into microbial cell wall, can disrupt its cell structure resulting in the leakage of intracellular compounds, and ultimately cell death.

Due to limited resources of fresh water, it is likely that in the near future, desalination of sea water will become a major source of fresh water. Conventional desalination technologies like reverse osmosis (RO) membranes are being used but these are costly due to the large amount of energy required. Nanotechnology has played a very important role in developing a number of low-energy alternatives, among which three are most promising. (i) protein-polymer biomimetic membranes, (ii) aligned-carbon nanotube membranes and (iii) thin film nanocomposite membranes [46]. These technologies have shown up to 1000 times better desalination efficiencies than RO, as these have high water permeability due to the presence of carbon nanotube membranes in their structure. Some of these membranes are involved in the integration of other processes like disinfection, deodorizing, de-fouling and self-cleaning. Some of these technologies may be introduced in the market place in the near future but scale-up fabrication, practical desalination effectiveness and long-term stability are the most critical challenges to be considered before their successful commercialization.

Ligand based nanocoating can be utilized for effective removal of heavy metals as these have high absorption tendency. It becomes cost effective as it can be regenerated in situ by treatment with bifunctional self-assembling ligand of the previously used nanocoating media. Multiple layers of metal can be bonded to the same substrate using crystal clear technologies [47] and this technology is expected to be available in near future. According to [48], another strategy for the removal of heavy metals is the use of dendrimer enhanced filtration (DEF) and it can bind cations and anions according to acidity.

Crop growth and field conditions like moisture level, soil fertility, temperature, crop nutrient status, insects, plant diseases, weeds, etc. can be monitored through advancement in nanotechnology. This real-time monitoring is done by employing networks of wireless nanosensors across cultivated fields, providing essential data for agronomic intelligence processes like optimal time of planting and harvesting the crops. It is also helpful for monitoring the time and level of water, fertilizers, pesticides, herbicides and other treatments. These processes are needed to be administered given specific plant physiology, pathology and environmental conditions and ultimately reduce the resource inputs and maximize yield [3].

Scientists and engineers are working from dawn to dusk in developing the strategies which can increase the water use efficiency in agricultural productions, e.g. drip irrigation. This has moved precision agriculture to a much higher level of control in water usage, ultimately towards the conservation of water. More precise water delivery systems are likely to be developed in the near future. These factors critical for their development include water storage, in situ water holding capacity, water distribution near roots, water absorption efficiency of plants, encapsulated water released on demand, and interaction with field intelligence through distributed nano-sensor systems [43].

Sensing and detection of various contaminants in water at nanoscale under laboratory and field conditions has remained a hot issue over the last decade. In the near future, state-of-the-art nanotechnology-based techniques will help in developing many new technologies that will have better detection and sensing ability [1].