Chitosan Nanoparticle Delivery Systems for Sustainable Agriculture PDF

International Journal of Biological Macromolecules 77 (2015) 36–51 Contents lists available at ScienceDirect International Journal of Biolo...

International Journal of Biological International Review Chitosan nanoparticle based delivery systems for sustainable agriculture Prem Lal Kashyap a,b,∗ , Xu Xiang b , Patricia Heiden b a ICAR-National Bureau of Agriculturally Important Microorganisms b Michigan Technological University (MTU), Houghton, a r t i c l e i n f o Article history: Received 18 October 2014 Received in revised form 3 February 2015 Accepted 16 February 2015 Available online 5 March 2015 Keywords: Chitosan Encapsulation Agriculture Plant protection Controlled release Nanoparticles Contents 1. Introduction.......................................... 1.1. Chitosan in crop production and protection..... 1.2. Chitosan as a promising delivery system........ 1.3. Strategies for production of chitosan 1.4. Emulsion cross-linking......................... 1.5. Emulsion-droplet coalescence................... 1.6. Ionotropic gelation............................ 1.7. Precipitation.................................. 1.8. Reverse micelles............................... 1.9. Seiving method................................. 1.10. Spray drying.................................. 1.11. Strategies for loading active ingredient 1.12. Release kinetics of active ingredients 2. Applications of chitosan nanoparticles as a delivery 2.1. Pesticide delivery for crop protection......... 2.2. Fertilizer delivery for balanced and sustained 2.3. Herbicide delivery for weed eradication........ 2.4. Micronutrient delivery for crop growth ∗ Corresponding author at: ICAR-National Bureau of E-mail address: [email protected] (P.L. Kashyap). P.L. Kashyap et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 37 ........................................................................................ 47 n....................................................................................... 47 ............................................................................................ 48 ............................................................................................ 48 nanoparticles [65,66]. Chitosan has also known for its broad spec- trum antimicrobial and insecticidal activities [67,68]. Further, it is biodegradable giving non-toxic residues with its rate of degrada- tion corresponding to molecular mass and degree of deacetylation [69,70]. However, the low solubility of bulk chitosan in aqueous media limits its wide spectrum activity as an antimicrobial agent. Therefore, various strategies have been employed to enhance its antifungal potential. Chitosan is able to chelate various organic and inorganic compounds, making it well-suited for improving the stability, solubility and biocidal activity of chelated fungicides or other pesticides. For example, copper (Cu) compounds are well known for their antifungal nature and have been used with chi- tosan for antibacterial and antifungal activities. The majority of the research on chitosan nanoparticles in agricultural research studied their biocidal and antagonistic effects on bacteria and fungi, and gave encouraging results [71–73]. Chitosan-based nanocompos- ite ﬁlms, especially silver-containing ones, showed antimicrobial activity against several pathogens , but some effect was also observed with chitosan ﬁlms alone. Other studies investigated the use of chitosan–PVA hydrogels for antimicrobial and food pack- aging applications [76–78]. The combination of silver nanoparticles within a chitosan–PVA polymeric material also emerged as one of the most promising candidates for new antimicrobial materials to absorb. Recently, application of chitosan particles loaded with copper has been reported in waste water treatment [79,80]. Considering the growing interest, and recent advances, in chitosan-based nano- materials in medical and pharmacological applications, the purpose of this article is to review the current and ongoing research and developmental efforts into chitosan nanoparticles as a delivery sys- tem, with particular focus on describing methods that would be suitable for promoting crop productivity. 1.1. Chitosan in crop production and protection There have been several reports describing the use of chitosan for biotic and abiotic stress management in agriculture [73,81–85]. Table 3 lists some of the applications of chitosan in crop pro- duction and protection. For the ﬁrst time, Allan and Hadwiger described the application of chitosan as an antimicrobial agent. This has led to the exploitation of its antimicrobial potential in various sectors of agriculture. Since the 1980s, the study of chitosan has been shift from a general sewage treatment agent to plant growth regulator, soil conditioner, vegetables and fruits antistaling agent, and seed coating agent, especially in the crop disease management. Several studies showed that chitosan is not only an antimicrobial agent but also an effective elicitor of plant systemic acquired resistance to pathogens [73,82,84,131]. This polymer has been reported to be the enhancer and regulator of plant growth, development and yield [85,132,133]. Chitosan has been demonstrated to induce plant defences in tomato [87,89], cucumber , chilli seeds , strawberry fruits and rose shrubs. Chitosan can activate innate immunity by stimulating hydrogen peroxide (H2 O2 ) production in rice [134,135], induce a defense response by nitric oxide (NO) pathways in tobacco [136,137], promote the development and drought resistance of coffee , support the synthesis of phytoalexin , impact the jasmonic acid–ethylene (JA/ET) signaling marker in oilseed rape , cause changes in protein phosphorylation , activate mitogen-activated protein kinases (MAPKs) and trigger et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 Institute(s)/company Reference US based company (ETC Group, 2004) into the product to Advanced Materials Laboratory, Institute of Advanced Technology (ITMA), Malaysia University of Hong Kong, Hong Kong SAR, China. acid with carboxyl Wuhan University, Wuhan, China; Chinese Academy of Sciences, Beijing, China Beijing University of Chemical Technology, Beijing, China (validamycin) University of Ulster, UK University of Crete, GR Iowa State university, US Syngenta Crop Protection, Greensboro, NC Université de Perpignan via Domitia, Perpignan, France; Institute for Bioengineering of Catalonia, Barcelone, Spain Canadian Universities and Ontario Ministry of Agriculture, Food and Rural Affairs, CA Huazhong Agricultural University, Wuhan, China Central Food Technological Research Institute, Mysore, India. Institute of Animal Reproduction and Food Research, Tuwima, Poland during storage University of Manitoba, Winnipeg Central Food Technological Research Institute, Mysore, India. MingDao University, Taiwan; National Chung-Hsing University, Taiwan Geohumus-Frankfurt, DE Beijing University of Technology, China Universidad de Chile, Chile IFAPA, Centro Alameda del Obispo, Área de Mejora y Biotecnología, Córdoba, Spain; CSIC-Universidad de Zaragoza, Spain; CSIC, Instituto de Agricultura Sostenible, Alameda Córdoba, Spain UNESP—Univ. Estadual Paulista, Brazil; UNICAMP, Cidade Universitária Zeferino, Brazil; University of Sorocaba, Sorocaba, SP, Brazil G.B Pant University of Agri. & Tech., Pantnagar, India; National Physical Laboratory, New Delhi, India Huazhong University of Science and Technology, Hubei China; Chinese Academy of Agricultural Sciences-Key Laboratory for of salicylic acid in oil Genetic Improvement of Oil Crops, China Ningbo Municipal Center for Disease Control and Prevention, Zhejiang, China. (Dipel, Siven 85% Universiti Kebangsaan Malaysia, Malaysia VIT University, India University of Adelaide, AU CSIRO Land and Water, AU Kansas State University, US Área de Mejora y Biotecnología, Córdoba, Spain Indian Institute of Science (IIS), Bangalore, India; National Bureau of Agriculturally Important Insects (NBAII), India China Agricultural University, China UNESP—Univ. Estadual Paulista, Brazil; UNICAMP, Cidade for control release Universitária Zeferino, Brazil; University of Sorocaba, Sorocaba, SP, Brazil and Max Rubner Institut, Karlsruhe, Germany UNESP—Univ. Estadual Paulista, Brazil; UNICAMP, Cidade Universitária Zeferino, Brazil; et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 39 of chitosan naoparticles and their applications as a delivery system in agriculture. controlled release matrices in agriculture. Active ingredient Characteristics Reference(s) CuSO4 Enhanced antifungal activity against Alternaria alternate, Macrophomina phaseolina and Rhizoctonia solani ␣-Fe3 O4 Heavy metals monitoring with low detection limit Urea Controlled release of the urea fertilizer Silver nanoaprticles Size of 13 nm; exhibits good antibacterial activity Imazaquin (Herbicide) Porous spherical beads of 2.31 mm size; sustained slow release of active material Atrazine (Herbicide) and Sustained release of active material in water for imidacloprid 572 h for atrazine and 24 h for imidacloprid, respectively Auxins (Agrochemical) Chitosan microspheres extended action of auxin release (up to 120 h) Paraquat (Herbicide) Sustained release of active material in water for 8 h Silver nanoparticles Pesticide removal for extended periods Urea, calcium phosphate and Size of 78 nm; controlled release of the NPK potassium chloride fertilizer Potassium nitrate (KNO3 ) and Hydrogel in the form of circular pads with 2 mm in Dihydrogen ammonium thickness and 120 mm in diameter; controlled phosphate [(NH4 )2 HPO4 ] release of the potassium fertilizer; enhanced up to 25% water retention of the soil 3-Hydroxy-5-methylisoxazole Size of 5 ␮m; sustained release of active material (Herbicide) in water for 80–160 h Atrazine (Herbicide) and urea Extended release period of atrazine to 7 months; (Fertilizer) chitosan-coated urea beads extended action of urea release (up to 180 h) Beauvericin (Pesticidal Improved pesticidal activity against groundnut cyclodepsipeptide) defoliator Spodoptera litura Imidacloprid (Insecticide) A novel photodegradable insecticide; controlled and sustained release of midacloprid; showed toxicity against Martianus dermestoides adults Dichlorprop (Herbicide) Enhanced toxicity to fresh water green algae and slow release of Dichlorprop Brassinosteroids (Hormones) Controlled delivery of brassinosteroids with biological activity as agrochemicals Dichlorprop (Herbicide) Controlled and slow release of dichlorprop Hexavalent chromium (Metal) Effective agent for in situ subsurface environment remediation Rotenone (Insecticide) Useful as a prospective carrier for control released agrochemical 1-Naphthylacetic acid Controlled and slow release of 1-Naphthylacetic (Hormone) acid et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 chitosan use for plant growth promotion and protection from 1984 to 2015. of chitosan application Reference activity against Fusarium solani due to synthesis and elicitation of pisatin phytoalexin resistance of tomato plants to the crown and root rot pathogen Fusarium oxysporum f. sp. sici activity against postharvest pathogens of systemic resistance to Fusarium crown and root rot in the incidence and severity of Fusarium yellows biomass production and yield by decreasing transpiration and water use by 26–43% in endogenous hormone content, alpha-amylase activity and chlorophyll content in in respiration rate of germination seeds, root vigor, chlorophyll, protein content and in seedlings as well as nitrate reductase and amylase activities in the seed germination rate in the energy of germination and germination percentage in growth and yield of gray mold infection in plants caused by Botyrtis cinerea in yield and late blight resistance by Arbuscular mycorrhizal fungi band chitosan sprays resistance against foliar diseases activity against Fusarium oxysporum f. sp. albedinis and elicitor of defence reactions resitance against Colletotrichum sp.; promote of seedling growth of plant defence system against gray mold and downy mildew of defence response against Pyricularia grisea activity against anthracnose and improvement in quality retention of papaya during storage of callose apposition and abscisic acid accumulation in response to Tobacco necrosis virus seed germination and seedling vigor chilling tolerance of maize seedlings and induced higher activities of antioxidative enzymes defense-related enzymes activity antifungal activity against Botrytis bunch rot and induction of defense-related enzymes quality attributes and extended the postharvest life by inducing defense-related enzymes effects of postharvest heat treatment and chitosan coating on quality and antimicrobial of fresh cut mangoes xanthone-rich extracts with antifungal activity phosphatidic acid and nitric oxide inhibition activity against fruit rot the uptake of nutrients, nitrogen, potassium and phosphorous, decreased cadmium application of chitosan (100 ppm) enhanced growth and fruit yield the production of H2 O2 and nitric oxide blight induced activity of defense-related enzymes in the germination and growth performance of ajowan (Carum copticum) under salt activity of antioxidant enzymes positive and promising effects in increasing rice yield and inhibiting brown backed rice killing effect and protection from fruit blotch disease brown rot infection and enhanced antioxidant and defense-related enzymes the expression level of defense-related enzymes and Pitch canker H2 O2 , defense-related enzymes, and soluble protein and Anthracnose coating served as carriers for bioactive compounds fungicide for controlling Fusarium crown and root rot application as a plant growth regulator could increase the germination rate of cucumber, chilli, pumpkin and cabbage. Manjunatha et al. reported that seed priming with chitosan enhances seed germination and seedling vigor in pearl millet. Further, it is also noticed that seed priming with acidic chitosan solutions improved the maize vigor. Similarly, rice seedlings treated with chitosan induced defense responses against the rice blast pathogen, Magnaporthe grisea by inducing the production of the phytoalexins (sakuranetin and monilactone A) in leaves. Moreover, chitosan also stimulated the growth and yield of rice along with reinforcing the defense response. In addition, other studies also supported a role of chitosan in modulating the plant response to several abiotic stresses including salt and water stress [121,138,150]. For instance, Boonlertnirun et al. found that chitosan treatments had a signiﬁcant effect on the growth or yield of drought-stressed rice plants compared to et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 41 of chitosan encapsulated active compounds. Cons Reference(s) procedure; no chemical Release of active ingredient depends on [66,158–162] the possible toxic side molecular weight, degree of deacetylation, and or reagents used in the concentration of chitosan control of degradation efﬁciency; controlled Tedious process, uses harsh crosslinking [40,66,159,161,163] bioavailability; and agents, problem of reactivity of active agent with cross-linking agent, and challenge of complete removal of unreacted cross-linking agent and smaller particle Particle size depends on the degree of [66,164] deacetylation of chitosan. The decreased degree of deacetylation increases particle size which in turn decreases drug content of particle size and drug Partial protection of the loaded active agent [40,159] the use of toxic organic from nuclease degradation stable particle size with Tedious and laborious process [40,66] index; and narrow size smaller particle size and can be easily scaled up Irregular particle shape Particle size depends on size of nozzle, spray [40,159] drug release attributes ﬂow rate, pressure inlet air temperature; and encapsulation efﬁciency depends on the molecular weight of chitosan of molecular weights (500–1400 kDa) and degrees of acetylation. Chitosan’s amine group also readily lends itself to other chem- ical modiﬁcations. Chitosan easily absorbs to plant surfaces (e.g. leaf and stems), which helps to prolong the contact time between agrochemicals and the target absorptive surface. Chitosan nanopar- ticles are known to facilitate active molecule or compound uptake through the cell membrane. The absorption enhancing effect of chi- tosan nanoparticles improves the molecular bioavailability of the active ingredients contained within the nanoparticles. Taken together, these advantages indicate that chitosan has a bright future as a drug delivery system in the ﬁeld of sustainable agriculture. 1.3. Strategies for production of chitosan nanoparticles and Chitosan nanoparicles can be synthesized by various techniques viz., emulsion cross-linking, emulsion-droplet coalescence, precip- itation, ionotropic gelation, reverse micelles and sieving through nano-scaled controlled release devices. A comparison of these tech- niques, their merits and demerits are summarized in Table 4. The selection of methods for chitosan nanoparticles synthesis depends on requirements such as the particle size and shape, thermal sta- bility, release time of the active ingredients, and residual toxicity of the ﬁnal product. 1.4. Emulsion cross-linking Emulsions are a standard process leading to nanoparticulate phases, while cross-linking is a common way to stabilize a par- ticle structure and to manipulate the controlled-release properties of that particle. Altering the cross-linking degree of a particle modiﬁes an agrochemical’s permeability through it. Cross-linking enhances the mechanical strength of the ﬁnal particle by introduc- ing a three-dimensional network structure into the nano-emulsion. The process begins when a chitosan solution is emulsiﬁed in an oil phase (water-in-oil emulsion). The chitosan phase is ﬁrst stabilized by a suitable surfactant, and is then reacted with an appropriate cross linking agent (e.g. formaldehyde, glutaraldehyde, genipin, glyoxal, etc.). This is followed by washing and drying of the resulting nanoparticles. This method is schematically represented in Fig. 2(A). The particle size is mainly determined et al. / International Journal of Biological Macromolecules 77 (2015) 36–51 the synthesis of chitosan nanoparticles. (A) Emulsion cross-linking; (B) emulsion-droplet coalescence; (C) ionotropic sieving; and (G) spray drying. The term ‘drug’ is used to represent an agrochemical compound, micronutrient and genetic / International Journal of Biological Macromolecules 77 (2015) 36–51 43 Fig. 2. (Continued ). somewhat tedious and the use of harsh, and often expensive, cross- linking agents can induce undesirable chemical reactions with the active agent. Recently, Fan et al. studied the synthesis and controlled release characteristics of auxin-loaded chitosan micro- spheres using a cross-linker. They found that the cumulative release al. / International Journal of Biological Macromolecules 77 (2015) 36–51 CS chains and impels the formation of irregular and smaller size nanoparticle cores. At even higher ␤ ratios, the very low concen- tration of TPP results in low nanoparticle core densities because of the increased distance between successive H-links, ultimately lead- ing to an increased nanoparticle size. Besides this, a recent work on chitosan/TPP nanoparticles has also established that the concentra- tion of acetic acid used to dissolve chitosan and the temperature at which the cross-linking process occurs, strongly affect the size dis- tribution of the obtained nanoparticles. Fàbregasa et al. found that the stirring speed during ionic gelation signiﬁcantly affect reaction yield. Therefore, manipulation of this parameter can be used to give some control over size range that is obtained to favor the maximum yield of nanoparticles of desired size. oil. The 1.7. Precipitation This method is quite simple. Chitosan nanoparticles are pro- duced by blowing a chitosan solution into an alkaline solution [e.g. NaOH(aq) ] or methanol. The blowing is accomplished with a com- pressed air nozzle, thereby forming the coacervate particles. These are separated and puriﬁed by ﬁltration and followed by washing with hot and cold water. The method is schematically repre- sented in Fig. 2D. Generally, various parameters viz., compressed air pressure, spray nozzle diameter and chitosan concentration affects the particle shape and size. Although this method is simple, cross- linking is required to enhance the particle stability, and even then particles have weak mechanical strength and irregular morphol- ogy. 1.8. Reverse micelles This method uses a thermodynamically stable mixture of water, oil and lipophilic surfactant. Using this method, it is possible to obtain very small polymeric nanoparticles (≤10 nm) with a uniform distribution compared with other methods. The size, polydisper- sity and thermodynamic stability of the particles are maintained in a dynamic equilibrium system. Brieﬂy, the method consists of preparing a surfactant solution (e.g. sodium bis(ethyl hexyl) sul- fosuccinate or cetyl trimethylammonium bromide) in an organic solvent (e.g. n-hexane), to which a chitosan solution and the active ingredient are added under constant stirring, forming a transpar- ent mini- or micro-emulsion. Subsequently, a cross-linking agent (e.g. glutaraldehyde) is added and the system is maintained under constant agitation. The organic solvent is then evaporated, pro- ducing a dry and transparent mass that is dispersed in water. A salt is then added to this system, which precipitates the surfac- tant. The resulting mixture is centrifuged and the supernatant, containing nanoparticles loaded with the active substance, is col- lected. The nanoparticles are separated by dialysis and lyophilized to obtain a dry powder. The method is schematically repre- sented in Fig. 2E. Brunel et al. used a reverse micellar method to prepare chitosan nanoparticles. They emphasized that chitosan of low molecular weight is preferable to achieve better control over particle size and distribution. This may be due to a reduction in the viscosity of the internal aqueous phase or entanglement of the polymer chains during the process. In recent times, this method has been use for enzyme immobilization and to encapsulate oligonucleotides. To date, despite some of the advantages, the use of this method to produce chitosan nanoparticles is limited, due to the difﬁculty of isolating the nanoparticles and need to use a large quantity of organic solvent. between chi- 1.9. Seiving method the high con- This method involves the cross-linking of an aqueous acidic solution of chitosan using glutaraldehyde. The cross-linked / International Journal of Biological Macromolecules 77 (2015) 36–51 45 1.12. Release kinetics of active ingredients from chitosan nanoparticles The release of an active ingredient from chitosan-based parti- cles depends upon the morphology, size, density, and extent and rate of cross-linking of the particles, as well as the physicochemical properties of the drug. If any adjuvant is used this can also affect the release rate. Studies showed that under in vitro conditions, the release of an active ingredient is affected by pH, solvent polarity, and the presence of enzymes in the dissolution media [188,189]. Generally, the release of drug from chitosan particles occurs by one, or a combination of three different mechanisms: (i) an osmot- ically driven burst mechanism, (ii) a diffusion mechanism, and (iii) erosion or degradation of the polymer. In agricultural systems the release mechanisms are by diffusion release and/or degradation release. The diffusion release mechanism includes several steps typically viz., (i) penetration of water into particulate system, which causes swelling of the matrix; (ii) conversion of a glassy polymer into a plasticized or rubbery swollen matrix, and (iii) diffusion of com- and the pound from the swollen matrix. The original active ingredient content contained in chitosan par- is atom- ticles is determined in different ways, but the release from the chitosan particles, is typically measured from particles placed in phosphate buffer saline (PSB; pH 7.4) and kept in a thermostatic type of needle, incubator at 37 ◦ C. Speciﬁed volumes of the buffered medium are removed at regular intervals from the sample being analyzed, and that same amount of fresh buffer is added back into the ﬂask to keep the total solution volume constant throughout the duration and of the study. The aliquot of removed sample is then ﬁltered and the transparent ﬁltrate is analyzed. The quantity of active ingre- dient in the aliquot is typically determined by spectroscopic or chromatographic methods. Diffusion release of active ingredient is typical for hydrophilic polymers that form hydrogels (e.g. polyvinyl alcohol), while dif- fusion and degradation release occurs with chitosan. It is not uncommon to observe an initial “burst” release of active ingre- dient from particles that predominantly release active ingredient by diffusion or degradation. This happens due to the adsorption of active ingredients onto the surface of the particles. Once this burst is exhausted, a slow and steady release is observed that accel- erates if and when the particle matrix begins to degrade. Kweon and Kang synthesized chitosan–polyvinylalcohol (PVA) par- ticles to study the compound release mechanism of the active ingredient under various conditions. They calculated the diffusion controlled release by analysis of the linear relationship between the amount of active ingredient released and the square root of the time. Jamnongkan and Kaewpirom demonstrated potas- sium release kinetics and water retention of controlled-release fertilizers based on chitosan hydrogels is through a quasi-Fickian diffusion mechanism. Similarly, Jameela et al. obtained a good correlation ﬁt for the cumulative drug released vs. square root of time, demonstrating that the drug release from the microsphere matrix is diffusion-controlled and obeys the Higuchi equation precipitate. It was demonstrated that the rate of release depends upon the size of microspheres. Orienti et al. studied the correlation between matrix erosion and release kinetics of indomethacin- loaded chitosan microspheres. Release kinetics was correlated with the concentration of chitosan in the microsphere and pH of the release medium. Nam and Park have demonstrated the in vitro release test of drug loaded chitosan microspheres. Agni- hotri and Aminabhavi also analyzed the dynamic swelling data of chitosan microparticles and concluded that with increase in cross-linking, swelling of chitosan microparticles decreases. Recently, Khan and Ranjha studied the swelling behavior of chitosan/poly(vinyl alcohol) hydrogels as a function of pH, poly- meric compositions and degree of cross-linking. They noticed that / International Journal of Biological Macromolecules 77 (2015) 36–51 used as carriers of the essential oil of Lippia sidoides, which pos- sesses insecticidal properties. The ﬁndings indicated the suitability of chitosan for use as matrices to carry bioinsecticides designed to control the proliferation of insect larvae. Similarly, microcapsules of alginate and chitosan were prepared, characterized, and evalu- ated as a carrier system for imidacloprid. The particles obtained were stable and imidacloprid was encapsulated with an efﬁciency of around 82%. In release assays, it was shown that the release time of the encapsulated insecticide was up to eight times longer, compared to the free insecticide, and that alterations in the con- centrations of alginate and chitosan affected the release proﬁle. In another independent study, Quiñones et al. described the use of chitosan microspheres to carry synthetic analogs of brassinos- teroids and diosgenin derivatives. The release kinetics assay using water revealed that the least efﬁciently encapsulated steroids were released fastest from the particles. These results demonstrate that molecular modiﬁcations can be used to design effective systems for the delivery and release of agrochemicals. Besides this, amphiphilic derivative of chitosan, N-(octadecanol-1-glycidyl ether)-O-sulfate chitosan has been evaluated as a carrier for the insecticide rotenone. The polymeric micelles formed were spherical, with a size range of between 167 and 204 nm, and the nanoparticles were formed by self-assembly in aqueous solution. The encapsulation of rotenone increased its solubility in water 1300-fold, while in vitro release assays demonstrated that the nanoparticles provided sus- tained release of the insecticide. The properties of nanomicelles based on NOSCS enable them to be used as carriers to encapsulate and subsequently release insoluble pesticides employed in agri- culture. Feng and Peng synthesized a new compound based on chitosan, using carboxymethyl chitosan (CM-C) with ricinoleic acid (RA) for use as a carrier of the biopesticide azadirachtin (AZA). The particles presented good polydispersion, with a size range of 200–500 nm, as well as smooth spherical morphology and high zeta potential. The AZA encapsulation efﬁciency was 56%, and the par- ticles were able to release the pesticide over a period of 11 days. The use of the carrier assisted the solubilization in water of this lipid-soluble pesticide, and could therefore offer advantages in agri- cultural applications. signif- 2.2. Fertilizer delivery for balanced and sustained nutrition The extent and quality of plant growth is largely dependent on the quantity of fertilizer and water. So, improvement in crop outcomes requires improved utilization of water resources and fertilizer nutrients. It is estimated that about 40–70% of nitrogen, 80–90% of phosphorus, and 50–70% of potassium of the applied fertilizers is lost to the environment and cannot be absorbed by the intended plants. This is not only a substantial monetary and resource loss but also results in serious environmental pollution [50,205]. Several recent research studies have been published that describe the use of superabsorbent polymers to enhance germination and crop growth under arid and desert environments. The results are encouraging, and show that use of such materials can reduce water consumption in irrigation, and reduce the plant death rate [206,207]. An optimized combination of slow release fertilizers and superabsorbent polymers may not only signiﬁcantly improve plant nutrition and yields, but might be a method to mitigate the stressed environmental impact, reduce water losses to evaporation, and reduce irrigation frequency. Indeed, the development of slow release fertilizers from chitosan nano- or microparticles is a relatively new concept to reduce fertilizer con- sumption and to minimize environmental pollution. With these principles in mind, Wu et al. developed a chitosan-coated NPK compound fertilizer with both controlled-release and water- retention capabilities, by using an inner coating of chitosan, and an outer coating was poly (acrylic acid-co acrylamide) [P(AA-co-AM)], al. / International Journal of Biological Macromolecules 77 (2015) 36–51 47 the enantioselective bioavailability of the herbicide, which could be of use in environmental protection applications. chitosan 2.4. Micronutrient delivery for crop growth promotion nor their It is a well known fact that micronutrients like manganese, boron, copper, iron, chlorine, molybdenum, and zinc promote opti- mum plant growth. Steady increases in crop yields following the 1960s ‘green revolution’ has progressively depleted the level of essential micronutrients like zinc, iron and molybdenum in the soil. Farming practices, such as liming acid soils, contribute to micronutrient deﬁciencies in crops by decreasing the availabil- ity. Foliar application of micronutrients is now a common agricultural practice and is shown to enhance its uptake by the leaves. Nanoformulations of micronutrients may be used to spray crops for enhanced foliar uptake, or nanomaterials with micronutrients may be used as a soil addition for their slow release to promote plant growth and improve soil health. For an example, Tao et al. synthesized chitosan modiﬁed with 1- naphthylacetic acid, which is an important plant growth hormone. The results indicated that the release of the 1-naphthylacetic acid was strongly dependent on pH and temperature, and could con- tinue for 55 days at pH 12 and 60 ◦ C. Despite this dependence, the formulation offers potential for the slow release of plant growth hormones. 2.5. Soil health improvement production The installation of nanosensors in farmers’ ﬁelds is being applied to enable the real time monitoring of soil conditions and the early detection of potential problems such as nutrient depletion or insuf- ﬁcient water. In this context, nanosensors can help to extend the new practices of precision farming by detecting and rectifying agronomic problems in a very short time span. Nanomaterials, such as hydrogels and zeolites, were reported to be useful for improving the water-holding capacity of soil and to absorb environ- mental contaminants. Recently, efforts have been made to develop a nanoparticle modiﬁed chitosan sensor for the determina- tion of heavy metals. The biosensor is based on the combination of chitosan cross-linked with glutaraldehyde modiﬁed with para- magnetic Fe3 O4. The ␣-Fe3 O4 /CS nanocomposite ﬁlm, which can be easily prepared, exhibits high accumulation ability for the deter- mination and removal of heavy metals (arsenic, lead, and nickel) and ‘reports’ the process by an electrical response. Agnihotri et al. developed a novel antimicrobial chitosan–PVA-based hydro- gel, which can behave both as a nanoreactor and an immobilizing matrix for silver nanoparticles (AgNPs) with promising antibacte- rial applications. showed that 2.6. Delivery of genetic material for plant transformation The biggest challenge for gene delivery in agricultural crops is the plant cell wall. Traditional gene transfer methods in plants such as Agrobacterium-mediated gene transfer, electroporation, PEG-mediated gene transfer, particle gun bombardment, etc., are costly, labor intensive and cause signiﬁcant perturbation to the growth of cells. In addition, these methods have very low efﬁ- ciency (0.01–20% efﬁciency). Nevertheless that has been relatively successful for genetic transformation of dicots. Hence, there is interest in utilizing novel delivery systems for the develop- ment of successful transformants. Nanotechnology has shown its value in the genetic modiﬁcation of plants by introducing new genes with a corresponding crop improvement. This system has signiﬁcant advantages in comparison to conventional and tradi- tional gene transformation tactics. Firstly, nanoparticle approaches are applicable to both monocot and dicot plants, irrespective of / International Journal of Biological Macromolecules 77 (2015) 36–51 transformations. There are some mixed results with regard to gene delivery via chitosan nanoparticles, but given the potential advan- tages of chitosan nanoparticles to assist in the delivery of genetic material to design new and improved plant genotypes, chitosan will continue to be an important research topic. And, there is a real potenital to use DNA-coated chitosan nanoparticles as a nanocar- rier in a gene gun system, for bombardment of plant cells and tis- sues to achieve efﬁcient and targeted gene transfer, in near future. 3. Conclusions be devel- Application of chitosan based nanoparticles in agriculture is still in a nascent stage. Encouraging and promising results are already being achieved

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