Nano-Pesticides and Nano-Herbicides

Nanotechnology has potential for efficient delivery of chemical and biological pesticides using  nanosized preparations or nanomaterials based agrochemical formulations. The active ingredient is adsorbed, attached, encapsulated or entrapped unto or into the nano-matrix. Controlled release of the active ingredient is achieved due to the slow release characteristics of the nanomaterials, bonding of the ingredients to the material and the environmental conditions. The benefits of NMs based formulations are the improvement of efficacy due to higher surface area, higher solubility, higher mobility and lower toxicity due to elimination of organic solvents. Nanopesticides involve either very small particles of pesticidal active ingredients or other small engineered structure with useful pesticidal properties. Nanopesticides can increase the dispersion and wettability of agricultural formulations and unwanted pesticide movement. Nanomaterials and biocomposites exhibit useful properties such as stiffness, thermal stability, solubility, permeability, crystallity and biodegradability needed for formulating  nanopesticide.  Nanopesticides also offer large specific surface area and hence increased affinity to the target. Nanoemulsions, nanoencapsulates, nanocontainers and nanocages are some of the nanopesticides delivery techniques that have been discussed recently. Nanopesticides delivery techniques have the ability to control or delayed delivery, absorption and more effective and environmentally friendly approach. Currently spraying of pesticides involves wither knapsacks that deliver large droplets associated with splash loss or ultralight volume sprayer for controlled droplet application with smaller droplets causing spray drift. Constraints due to droplet size may be overcome by using NP encapsulated or nanosized pesticides that will contribute to efficient spraying and reduction of spray drift and splash losses. 

Basically, the nano-formulation should degrade faster in the soil and slowly in plants with residue level below the regulatory criteria in food stuff. The sodium dodecyl sulphate (SDS) is used to increase the photo-degradation of the nanoparticles in soil. The SDS modified Ag/TiO₂ imidacloprid nanoformulation has been developed using a microencapsulation technique that used chitosan and alginate. Formulation stability is also an important aspect at the nano level.  A stable nanopesticide (bifenthrin) using polymer stabilizer such as Polyvinylpyrrolidone (PVP), Polyvinyl alcohol (PVOH), and Poly(acrylic acid)-b-poly(butyacrylate (PAA-b-PBA) has been formulated successfully.

Plants provide a non-toxic source of molecules with proven biological efficacy that are usually non-persistent in fresh water and soil. However, phytochemcials such as secondary metabolites and essential oils face problems of stability and cost effectiveness. Incorporation of Artemisia arborescens essential oil into solid lipid NPs (200-204 nm) reduced the rapid evaporation of essential oil. Amorphous nanosilica is obtained from various sources such as the shell wall of phytoplankton, volcanic soil, displayed promising potential as a biopesticide. Nano-silica may be useful against stored grain, household pests, fungal organism, worms etc.

Bacteria, viruses and fungi can function as biological control agents against insect pests. Bacterial and viral formulations need to be ingested by the host and are susceptible to desiccation, heat and UV inactivation. The use of nano-formulations may offer new ways to enhance the stability of these biological agents. Mycopesticides or fungal biocontrol agents are promising as they act by contact and do not need ingestion, can be easily mess produced, and are relatively specific. Microbial products such as enzymes, inhibitor, antibiotics and toxins are promising as biopesticides against plant pests and pathogens. The insecticidal properties of bacterial toxins (Bt) are well known. However, microbial products need stabilization and directed delivery mechanism towards identified targets. Chitosan or clay as stabilizing and delivery agents have potential of biocompatible and biodegradable nanomaterials.

Unwanted plants along with the desired plant crops are called weeds. To kill these weeds, herbicides are used but conventional herbicide when sprayed has a chance of getting affected to the foods crops too by this and there can be huge loss in the crop yield. By using nano herbicide which is 1-100 nm range will try to mingle with the soil particle and try to destroy the entire weeds from their roots by not affecting other food crops. As the nanoparticles are target specific they can be used to kill the weeds and destroy it to get better yield. Herbicides like atrazine, triazine could be encapsulated to get efficient release to the plants.

 

Nano-Fertilizers and Nano-Biofertilizers

Much of the fertilizers are unavailable to plants as they are lost as run-off causing pollution. Localized application of large amount of fertilizer, in the form of ammonium salts, urea and nitrate or phosphate compounds are harmful. Nanomaterials have potential contribution in slow release of fertilizers. Fertilizers with sulphur nanocoatings are useful slow release fertilizers. In addition to sulphur nanocoatings or encapsulation of urea and phosphate and their release will be beneficial to meet the soil and crop demands. Other nanomaterials with potential applications include kanolin and polymeric biocompatible NPs. We can use biodegradable, polymeric chitosan NPs for controlled release of the NPK fertilizer sources such as urea, calcium phosphate and potassium chloride. Biofertilizers are live formulations of beneficial microorganism such as the fungal mycorrhizae, plant growth promoting rhizobacteria  Rhizobium, Azotobacter, Azosprillum and blue green algae, phosphate solubilizing bacterial Pseudomonas sp and Bacillus sp. Some constraints in their widespread usage are short shelf life, lack of suitable carrier materials, susceptibility to high temperature, problems in transportation and storage.  Potential application of polymeric NPs are for coating of biofertilzer preparations to yield formulations that are resistant to desiccation. Micronutrients promote optimum plant growth. Supplementation of soil with micronutrients trapped in NMs for their slow release would promote plant growth and soil health. 

NANOTECHNOLOGY IN AGRICULTURE

Crop production and growth severely decrease under stress. Environmental stress conditions such as drought, heat, salinity, cold or pathogen infection can have a devastating impact on plant growth and yield. As traditional approach for crop improvement reach their limits, agriculture has to adopt novel approaches such as nanotechnology to meet the demand of an ever-growing world population. Precision farming has been a long-derived goal to maximize output (i.e. crop yield) while minimize inputs (i.e. fertilizers, pesticides, herbicides etc.) through monitoring environmental variables and applying targeted action. One application of nanotechnology in agriculture addresses low use efficiency of inputs. Controlled release mechanisms via nanoscale carriers avoids temporal overdose, reduce the amount of agricultural chemicals used and minimize input and waste.

Nanosensors are devices that respond to environmental conditions converting them to a useful form of information.  They are capable of detecting very small amounts of contaminants, nutrients, pests and even stress caused by drought, temperature and nutrient deficiencies or pathogen presence. This detection engages nano delivery systems that deliver nutrients to crops with high precision. Smart precision farming makes use of computers, global satellite positioning system (GPS) and remote sensing devices to measure highly localized environmental. Networks of wireless nanosensors positioned throughout cultivated fields guarantee real-time monitoring of the crop growth provide essential data leading to better agronomic practices. Nanotechnology may be developed and deployed for real-time monitoring of the crop growth and field conditions including moisture level, soil fertility, temperature, crop nutrient status, insects, plant diseases, weeds. Networks of wireless nanosensors positioned across cultivated fields provide essential data leading to best agronomic intelligence processes with the aim to minimize resource inputs and maximize output and yield. Smart sensors and smart delivery systems will help in enhancing productivity in agriculture by providing accurate information and thus help maintaining farms and fields with precise control and report timely needs of crops; and consequently helping farmer to make better decision.

               The potential applications and main key focus areas for nanotechnology in agricultural research are:

     ·     Slow release of nanomaterials-assisted fertilizers, biofertilizers           and   micronutrients for efficient use
·      Delivery of nanocides i.e. pesticides encapsulated nanomaterials           for control release,
·        Stabilization of biopesticides with nanomaterials,
·        Agricultural diagnostics,
·        Water retention,
·        Nano-genetic manipulation of agricultural crops,
·        Nano-biosensors,
·        Nano-biofarming.

Nanotechnology: A Brief Introduction

The term ‘Nanotechnology’ was first defined in 1974 by Norio Taniguchi of the Tokyo Science University as the study of manipulating matter on an atomic and molecular scale. The definition of nanotechnology is based on the prefix ‘nano’ which is from the Greek word meaning ‘dwarf’. Technically the word ‘nano’ means one billionth of something. A nanometer is one billionth of a meter. The word nanotechnology is generally used when referring to materials with the size of 1 to 100 nanometers (nm). Nanotechnology is a new branch of science that deals with the generation and alteration of materials to nanosize. Materials with a particle size less than 100 nm at least in one dimension are generally classified as nanomaterials. These materials display different properties from bulk materials due to their size. These differences include physical strength, chemical reactivity, electrical conductance, magnetism and optical effects. Therefore, nanotechnology is the manipulation or self-assembly of individual atoms or molecule or molecular cluster into structures to create materials and devices with new or vastly different properties. Nanosensors and monitoring system enabled by nanotechnology will have a large impact on future precision methodologies. Hence, nanotechnology employs materials (NPs) having one or more dimension in the order of 100 nm or less.

Nanomaterials (NMs) of inorganic and organic origin are used for nanoparticles (NPs) synthesis by a variety of physical and chemical methods. The techniques for making nanoparticles are generally involved either a top-down approach or a bottom-up approach. In top-down approach, size reduction is achieved by various chemical and physical treatments such as milling, high pressure homogenization and sonication while in bottom-up synthesis, the nanostructure building blocks of the nanoparticles are formed first and then assembled to produce the final particle.

Among inorganic materials, metal oxide nanoparticles such as ZnO, TiO_2, AgO, MgO are of particular interest as they are physically and optically stable with tunable optical properties. Metallic nanomaterials are very interesting materials with unique electronic and electrocatalytic properties depending on their size and morphology and include the utilization of nanostructured materials with specific forms like quannologytum dots (QDs). Other inorganic materials such as montmorillionite and other clay nanoparticles have a structure of stacked platelets with one dimension of the platelet in the nanometer scale. Nano-clays have a high aspect ratio that provide more interactive surface when exfoliated and dispersed well. Organic materials such as carbon nanotubes, lipids and polymers are versatile materials with multiple applications.

Carbon nanotubes (CNTs) are hollow cylindrical tubes composed of one, two or several concentric graphite layers capped by fullerenic hemisphere, which are referred to as single-, double-, and multi-walled CNTs. The unique electronic, metallic and structural characteristics make CNTs an important class of materials. The possibility of electron transfer reaction due to their structure dependent metallic character and their high surface area provides ground for unique biochemical sensing system. Solid lipid nanoparticles are delivery systems that comprise of aqueous dispersion of solid lipids or dry powder such as triglycerides, steroids, waxes, long chain fatty acids and emulsifiers prepared by high pressure homogenization. Polymeric nanoparticles made from natural and synthetic polymers by wet synthetic routes are widely used due to their stability and ease of surface modification. Nanoparticles prepared from biopolymers or natural sources possess merits such as available from replenishable agricultural (cellulose, starch, pectin) or marine (chitin and chitosan) resources, biocompatibility, biodegradability and other ecological safety. Chitosan is one of the most promising NMs due to its excellent biocompatibility, complete biodegradiability and non-tixic nature. The degradation products of chitosan are harmless natural metabolites. It is obtained by the deacetylation of chitin, the second most abundant natural polymer after cellulose, which is found in the shells of crustaceans (crabs and shrimp), the cuticles of insects, and the cell walls of fungi. It is suitable for electrochemical sensors due to its transparent nature. Quantum dots (QDs) are inorganic nanocrystals, approximately 1-100 nm in size, with unique properties of broad excitation, narrow size-tunable emission spectra, high photochemical stability and negligible photoleaching. They have been widely used, mainly as alternative to fluorophores,  for the development of optical biosensors to detect ions, organic compounds and biomolecules such as nucleic acids, proteins, amino acids, enzymes, carbohydrates.  Dendrimers are known as organic macromolecules with tridimensional (3D) and highly defined structure functionality. The capability of these dendrimeric structures to stabilize and maintain the integrity of metallic nanoparticles has been reported.

Nanoparticles are generally characterized by their size, shape surface area, and disparity. The common techniques of characterizing nanoparticles are scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-visible spectrophotometery, X-ray diffraction (XRD), dynamic light scattering (DLS), energy dispersive spectroscopy (EDS).

Some nanomaterials and their applications

Nanomaterials

Applications

Inorganic Metal nanoparticles           AgO, TiO2, ZnO, CeO2; Fe2O3,          FePd, Fe-Ni; Silica; CdTe, CdSe   Clay         Montmorillonite layerd double hydroxides Organic  Carbon nanotubes,           nanofibres  Lipids       Liposomes       Lippolyplexes       Solid lipid nanoparticles Poymeric       Natural         Cellulose, Starch, Gelatin, Albumin         Chitin, Chitosan      Synthetic        Dendrimers        Polyethylene oxide        Polyethylene  glycol        Polylactides

Delivery of biomolecules (proteins, peptides, nucleic acids), biosensors, diagnostic techniques, pesticide degradation Delivery of pesticides, fertilizers, plant growth promoting hormones Biocatalysts, sensing, Delivery of DNA  and pesticides, essential oils Biocompatible, biodegradable Delivery of DNA/RNA Delivery of pesticides and DNA/RNA

Nanotechnology in Agriculture

The ‘First Green Revolution ‘ during 1970’s targeted to the four basic elements systems namely, semidwarf high yielding varieties of wheat and rice, extensive use of irrigation, fertilizers and agro-chemicals resulting in terrific increase in the agricultural production. However, the agricultural production is experiencing a plateau nowadays. Agriculture is always the backbone of many developing countries and facing a wide spectrum of challenges such as stagnation in crop yields, low nutrient use efficiency, multi-nutrient deficiencies, climate change, shrinkable arable land, water availability, shortage of labors.  There is a need of explore one of the frontier technologies such as ‘Nanotechnology’ to precisely detect and deliver the correct quantity of nutrients and pesticides to increase crop production and conservation of inputs. Precision farming has been a long-derived goal to maximize output (i.e. crop yield) while minimize inputs (i.e. fertilizers, pesticides, herbicides etc.) through monitoring environmental variables and applying targeted action.

Nanotechnology is now emerging and fast growing field of science which is being exploited over a wide range of discipline such as chemistry, physics, biology, material science, electronics, energy, medicines health sector and environment. Nanotechnology and applications derived from using nanotechnologies are of interest to agriculture to help address the issues of sustainable agricultural inputs and improving productivity and food and water safety. Nanotechnology have many applications in all stages of production, processing, storing, packaging and transport of agricultural products. Nanotechnology has the potential to revolutionise  the agricultural sector with new tools for the molecular treatment of disease detection, rapid disease detection, enhancing the ability of plants to absorb nutrients etc. In fact, there is a need of ‘Second Green Revolution’.