Graphene oxide as a pesticide delivery vector for enhancing acaricidal activity against spider mites

Advancing sustainable agriculture: a critical review of smart and eco-friendly nanomaterial applications

Undoubtedly, nanoparticles are one of the ideal choices for achieving challenges related to bio sensing, drug delivery, and biotechnological tools. After gaining success in biomedical research, scientists are exploring various types of nanoparticles for achieving sustainable agriculture. The active nanoparticles can be used as a direct source of micronutrients or as a delivery platform for delivering the bioactive agrochemicals to improve crop growth, crop yield, and crop quality. Till date, several reports have been published showing applications of nanotechnology in agriculture. For instance, several methods have been employed for application of nanoparticles; especially metal nanoparticles to improve agriculture. The physicochemical properties of nanoparticles such as core metal used to synthesize the nanoparticles, their size, shape, surface chemistry, and surface coatings affect crops, soil health, and crop-associated ecosystem. Therefore, selecting nanoparticles with appropriate physicochemical properties and applying them to agriculture via suitable method stands as smart option to achieve sustainable agriculture and improved plant performance. In presented review, we have compared various methods of nanoparticle application in plants and critically interpreted the significant differences to find out relatively safe and specific method for sustainable agricultural practice. Further, we have critically analyzed and discussed the different physicochemical properties of nanoparticles that have direct influence on plants in terms of nano safety and nanotoxicity. From literature review, we would like to point out that the implementation of smaller sized metal nanoparticles in low concentration via seed priming and foliar spray methods could be safer method for minimizing nanotoxicity, and for exhibiting better plant performance during stress and non-stressed conditions. Moreover, using nanomaterials for delivery of bioactive agrochemicals could pose as a smart alternative for conventional chemical fertilizers for achieving the safer and cleaner technology in sustainable agriculture. While reviewing all the available literature, we came across some serious drawbacks such as the lack of proper regulatory bodies to control the usage of nanomaterials and poor knowledge of the long-term impact on the ecosystem which need to be addressed in near future for comprehensive knowledge of applicability of green nanotechnology in agriculture.

Graphene as a nano-delivery vehicle in agriculture - current knowledge and future prospects

Graphene has triggered enormous interest in, and exploration of, its applications in diverse areas of science and technology due to its unique properties. While graphene has displayed great potential as a nano-delivery system for drugs and biomolecules in biomedicine, its application as a nanocarrier in agriculture has only begun to be explored. Conventional fertilizers and agricultural delivery systems have a number of disadvantages, such as: fast release of the active ingredient, low delivery efficiency, rapid degradation and low stability that often leads to their over-application and consequent environmental problems. Advanced nano fertilizers with high carrier efficiency and slow and controlled release are now considered the gold standard for promoting agricultural sustainability while protecting the environment. Graphene's attractive properties include large surface area, chemical stability, mechanical stability, tunable surface chemistry and low toxicity making it a promising material on which to base agricultural delivery systems. Recent research has demonstrated considerable success in the use of graphene for agricultural applications, including its utilization as a delivery vehicle for plant nutrients and crop protection agents, as well as in post-harvest management of crops. This review, therefore, presents a comprehensive overview of the current status of graphene-based nanocarriers in agriculture. Additionally, the review outlines the surface functionalization methods used for effective molecular delivery, various strategies for nano-vehicle design and the underlying features necessary for a graphene-based agro-delivery system. Finally, the review discusses directions for further research in optimization of graphene-based nanocarriers.

Multifunctional Nanoparticles and Nanopesticides in Agricultural Application

The unscientific application of pesticides can easily cause a series of ecological environmental safety issues, which seriously restrict the sustainable development of modern agriculture. The great progress in nanotechnology has allowed the continuous development of plant protection strategies. The nanonization and delivery of pesticides offer many advantages, including their greater absorption and conduction by plants, improved efficacy, reduced dosage, delayed resistance, reduced residues, and protection from natural enemies and beneficial insects. In this review, we focus on the recent advances in multifunctional nanoparticles and nanopesticides. The definition of nanopesticides, the types of nanoparticles used in agriculture and their specific synergistic mechanisms are introduced, their safety is evaluated, and their future application prospects, about which the public is concerned, are examined.

Interactions of airborne graphene oxides with the sexual reproduction of a model plant: When production impurities matter

The increasing use of graphene-related materials (GRMs) in everyday-life products raises concerns for their possible release into the environment and consequent impact on organisms. GRMs have widely varying effects on plants and, according to recent evidences, graphene oxide (GO) has the potential to interfere with the sexual reproduction owing to its acidic properties and production residues. Here, stigmas of the model plant Cucurbita pepo (summer squash) were subjected to simulated dry depositions of GO and GO purified from production residues (PGO). Stigmas were then hand-pollinated and GRM deposition was checked by ESEM and confocal microscopy. Analysis of stigma integrity, pH homeostasis and pollen-stigma interactions did not reveal negative effects. Fruit and seed production were not affected, but GO depositions of 22.1 ± 7.2 ng mm^-2 affected the normal development of seeds, decreasing seed dimensions, seed germination and germination speed. The elemental analysis revealed that GO has significant quantities of production residues, such as strong acids and oxidants, while PGO has only traces, which justifies the differences observed in the effects caused by the two materials. Our results show that GO depositions of up to 11.1 ± 3.6 ng mm^-2, which fall within the variation range of total dry particulate matter depositions reported in the literature, are safe for reproduction of C. pepo. This is the first "safety" limit ever recorded for depositions of "out-of-the-box" GO concerning the reproduction of a seed plant. If confirmed for wind-pollinated species, it might be considered for policymaking of GRMs emissions in the air.

Synergistic Effects of Graphene Oxide and Pesticides on Fall Armyworm, Spodoptera frugiperda

Fall armyworm Spodoptera frugiperda, a native insect pest in tropical and subtropical America, has rapidly spread to most parts of China and become a major pest of corn and other crops since invading in early January 2019. As an emergency and important control measure, chemical control of S. frugiperda has the advantages of quick effect and low cost. However, long-term and large-scale use of pesticides might pollute the environment and increase pest resistance. By improving the control effect and reducing the dosage of chemical pesticides, graphene oxide (GO) is used synergistically with insecticides to increase control efficacy to achieve low-cost and sustainable management of insect pests as a new type of synergist. In this study, graphene oxide was compounded with insecticides to form nanocomposites. To clarify pest physiological responses, the laboratory toxicity of graphene oxide-insecticide nanocomposites was measured on the larvae of S. frugiperda. The results demonstrated that GO could enhance the activity of four selected pesticides: chlorantraniliprole (Chl), beta cypermethrin (Bet), methoxyhydrazide (Met) and spinetoram (Spi). Compared with pesticides alone, the toxicity of Chl-GO, Bet-GO, Met-GO and Spi-GO mixtures to the third instar larvae of S. frugiperda increased by 1.56, 1.54, 2.53 and 1.74 times, respectively. The easy preparation and higher bioactivity of GO-pesticide nanocomposites indicated their promising application potential in pest control.

Effects of Nano-Graphene Oxide on the Growth and Reproductive Dynamics of Spodoptera frugiperda Based on an Age-Stage, Two-Sex Life Table

The development and reproduction of the fall armyworm (FAW), Spodoptera frugiperda, which were reared on artificial diets containing nano-graphene oxide (GO), were determined based on age-stage, two-sex life table analysis. The results showed that GO had adverse effects on FAWs. Compared with the control, the duration of the egg stage and first, second, and sixth instar larval stages increased with increasing GO concentrations; however, the lifespan of male and female adults decreased with increasing GO concentrations. Weights of FAW pupae that were supplied with GO-amended diets increased by 0.17-15.20% compared to the control. Intrinsic growth, limited growth, and net reproductive rates of FAWs feeding on GO supplemented diets were significantly lower than the control, while mean generational periods (0.5 mg/g: 38.47; 1 mg/g: 40.38; 2 mg/g: 38.42) were significantly longer than the control. The expression of genes encoding vitellogenin (Vg) and vitellogenin receptor (VgR) expression was abnormal in female FAW adults feeding on GO-amended diets; the number of eggs laid decreased relative to the control, but Vg expression increased. In conclusion, GO prolonged the developmental period of FAWs, decreased fecundity, and led to a decline in the population size. The study provides a basis for the rational use of GO as a pesticide synergist for FAW control.

The physio-chemical properties and applications of 2D nanomaterials in agricultural and environmental sustainability

Global hunger and nutritional deficiency demand the advancement of existing and conventional approaches to food production. The application of nanoenabled strategies in agriculture has opened up new avenues for enhancing crop yield and productivity. Recently, two-dimensional (2D) nanomaterials (NMs) have manifested new possibilities for increasing food production and nutrition. Graphene nanosheets, the 2D form of graphene has been exemplary in enhancing the loading capacity of agro-active ingredients, their target-specific delivery, bioavailability, and controlled release with slow degradation, resulting in the increased shelf-life/active time of the agro-active components. Also, the development of novel formulations/composites of MXenes and Transition Metal Dichalcogenides (TMDs) can foster plant growth, metabolism, crop production, protection and improvement of soil quality. Additionally, the 2D NM-based biosensors can monitor the nutrient levels and other parameters affecting agronomical traits in plants. This review provides an insight into the details of 2D NM synthesis and functionalization methods. Notably, the review highlights the broad-range of 2D NM applications and their suitability in the development of nanotechnology-based agriformulations. The 2D NM-based derivatives have shown immense potential in enhancing the pedologic parameters, crop productivity, pest-protection and nutritional value. Thus, assisting in achieving food and environmental sustainability goals.

Graphene-Delivered Insecticides against Cotton Bollworm

Nanopesticides can facilitate controlled release kinetics and efficiently enhance the permeability of active ingredients to reduce the dosage and loss of pesticides. To clarify the synergistic mechanism of graphene-insecticide nanocarriers against cotton bollworm, treatment groups, namely, control, graphene (G), insecticide (lambda-cyhalothrin (Cyh) and cyfluthrin (Cyf)), and graphene-delivered insecticide groups were used to treat the third-instar larvae of cotton bollworm. The variations in phenotypes, namely, the body length, body weight, and mortality of the cotton bollworm, were analyzed. The results show that graphene enhances the insecticidal activity of lambda-cyhalothrin and cyfluthrin against cotton bollworm. The two graphene-delivered insecticides with optimal compositions (3:1) had the strongest inhibitory effects and the highest mortality rates, with the fatality rates for the 3/1 Cyh/G and Cyf/G mixture compositions being 62.91% and 38.89%, respectively. In addition, the 100 μg/mL Cyh/G mixture had the greatest inhibitory effect on cotton bollworm, and it decreased the body length by 1.40 mm, decreased the weight by 1.88 mg, and had a mortality rate of up to 61.85%. The 100 and 150 μg/mL Cyh/G mixtures achieved the same mortality rate as that of lambda-cyhalothrin, thus reducing the use of the insecticide by one-quarter. The graphene-delivered insecticides could effectively destroy the epicuticle spine cells of the cotton bollworm by increasing the permeability and, thus, the toxicity of the insecticides.

Is airborne graphene oxide a possible hazard for the sexual reproduction of wind-pollinated plants?

Products containing graphene-related materials (GRMs) are becoming increasingly common, allowing GRM nanoparticles (NPs) to enter the environment during their life cycle. Thanks to their lightness and bidimensional geometry, GRM NPs can be easily dispersed in the air and travel very long distances. The flowers of wind-pollinated plants may be exposed to airborne GRMs, being apt to intercept pollen from the air and, inevitably, other airborne particles. Here, stigmas of four wind-pollinated plants (Corylus avellana, common hazel; Juglans regia, walnut; Quercus ilex, holm oak; Zea mays, maize) were exposed to airborne graphene oxide (GO) and GO purified from production residues (PGO) at a concentration of 3.7 ng m^-3. Subsequently, the stigmas were pollinated and the adhesion of GOs and their effects on stigma integrity and pollen-stigma interaction were examined. The effect of GO NPs in presence of liquid water on the stigma of C. avellana was also investigated. GOs NPs were intercepted by all species, but their effect varied among them. GO reduced pollen adhesion in J. regia and Q. ilex, whereas pollen germination was unaffected in all four species. The presence of a film of water neither completely removed GO NPs from the stigma, nor it enhanced the toxic effect of GO acidity. PGO never affected pollen-stigma interaction, indicating that the phytotoxic substances used for the production of GO, still in traces in commercial GO, are the main cause of GO toxicity. These results reconfirm the need to verify GRMs effects also on key biological processes beside single model organisms.

Advances in Biologically Applicable Graphene-Based 2D Nanomaterials

Climate change and increasing contamination of the environment, due to anthropogenic activities, are accompanied with a growing negative impact on human life. Nowadays, humanity is threatened by the increasing incidence of difficult-to-treat cancer and various infectious diseases caused by resistant pathogens, but, on the other hand, ensuring sufficient safe food for balanced human nutrition is threatened by a growing infestation of agriculturally important plants, by various pathogens or by the deteriorating condition of agricultural land. One way to deal with all these undesirable facts is to try to develop technologies and sophisticated materials that could help overcome these negative effects/gloomy prospects. One possibility is to try to use nanotechnology and, within this broad field, to focus also on the study of two-dimensional carbon-based nanomaterials, which have excellent prospects to be used in various economic sectors. In this brief up-to-date overview, attention is paid to recent applications of graphene-based nanomaterials, i.e., graphene, graphene quantum dots, graphene oxide, graphene oxide quantum dots, and reduced graphene oxide. These materials and their various modifications and combinations with other compounds are discussed, regarding their biomedical and agro-ecological applications, i.e., as materials investigated for their antineoplastic and anti-invasive effects, for their effects against various plant pathogens, and as carriers of bioactive agents (drugs, pesticides, fertilizers) as well as materials suitable to be used in theranostics. The negative effects of graphene-based nanomaterials on living organisms, including their mode of action, are analyzed as well.

Carbon-Based Nanomaterials for Sustainable Agriculture: Their Application as Light Converters, Nanosensors, and Delivery Tools

Nano-enabled agriculture is now receiving increasing attentions. Among the used nanomaterials, carbon-based nanomaterials are good candidates for sustainable agriculture. Previous review papers about the role of carbon-based nanomaterials in agriculture are either focused on one type of carbon-based nanomaterial or lack systematic discussion of the potential wide applications in agriculture. In this review, different types of carbon-based nanomaterials and their applications in light converters, nanosensors, and delivery tools in agriculture are summarized. Possible knowledge gaps are discussed. Overall, this review helps to better understand the role and the potential of carbon-based nanomaterials for nano-enabled agriculture.

Synergistic Antifungal Activity of Graphene Oxide and Fungicides against Fusarium Head Blight In Vitro and In Vivo

Plant pathogens constantly develop resistance to antimicrobial agents, and this poses great challenges to plant protection. Therefore, there is a pressing need to search for new antimicrobials. The combined use of antimicrobial agents with different antifungal mechanisms has been recognized as a promising approach to manage plant diseases. Graphene oxide (GO) is a newly emerging and highly promising antimicrobial agent against various plant pathogens in agricultural science. In this study, the inhibitory activity of GO combined with fungicides (Mancozeb, Cyproconazol and Difenoconazole) against Fusarium graminearum was investigated in vivo and in vitro. The results revealed that the combination of GO and fungicides has significant synergistic inhibitory effects on the mycelial growth, mycelial biomass and spore germination of F. graminearum relative to single fungicides. The magnitude of synergy was found to depend on the ratio of GO and fungicide in the composite. In field tests, GO–fungicides could significantly reduce the disease incidence and disease severity, exhibiting a significantly improved control efficacy on F. graminearum. The strong synergistic activity of GO with existing fungicides demonstrates the great application potential of GO in pest management.

Graphene environmental biodegradation: Wood degrading and saprotrophic fungi oxidize few-layer graphene

The environmental biodegradability profile of graphene related materials (GRMs) is important to know in order to predict whether these materials will accumulate in soil or will be transformed by primary decomposers. In this study, few-layer graphene (FLG) was exposed to living and devitalized axenic cultures of two white-rot basidiomycetes (Bjerkandera adusta and Phanerochaete chrysosporium) and one soil saprotrophic ascomycete (Morchella esculenta) with or without lignin, for a period of four months. Over this time, the increase of fungal biomass and presence of H₂O₂ and oxidizing enzymes [laccase/peroxidase and lignin peroxidase (LiP)] in growth media was assessed by gravimetric and spectrophotometric measurements, respectively. Raman spectroscopy and transmission electron microscopy (TEM) were used to compare the structure of FLG before and after incubation. All of the test fungi decreased pH in growth media and released H₂O₂ and laccase/peroxidase, but only basidiomycetes released LiP. Independent of growth media composition all fungi were found to be capable to oxidize FLG to a graphene oxide-like material, including M. esculenta, which released only laccase/peroxidase, i.e. the most common enzymes among primary decomposers. These findings suggest that FLG involuntarily released into terrestrial environments would likely be oxidized by soil microflora.

The combined adverse effects of cis-bifenthrin and graphene oxide on lipid homeostasis in Xenopus laevis

Simultaneous exposure to multiple pollutants has received great concerns considering that the interactions between pollutants can alter the environment fate and bioavailability of pollutants with potentially deleterious effects. Graphene oxide (GO) has been widely used in many areas including environmental remediation, biology and agriculture. However, researchers have largely ignored the combined toxicity of GO with coexisting toxicants. Cis-bifenthrin (cis-BF), a typical synthetic pyrethroid insecticide, was frequently detected in the environment, which raised the possibility of interaction between cis-BF and GO. Our study investigated the toxic effects of cis-BF alone or combined with GO on the lipid homeostasis in Xenopus laevis. Tadpoles at 51 stage were exposed to cis-BF (0, 12, 60 and 300 ng/L) or in their combination with GO (0.1 mg/L) for 21 days. Coexposure to cis-BF and GO deteriorated the lipid homeostasis disruption in tadpoles. The up- or down-regulation of lipogenesis genes expression and enzymes activity were amplified in the coexposure groups. Furthermore, the presence of GO enhanced the deleterious impacts of cis-BF on the hepatic function in tadpoles. This study uniquely shows that GO promotes the lipotoxicity and hepatic function deficit caused by cis-BF exposure in frog.

Development of leaf-adhesive pesticide nanocapsules with pH-responsive release to enhance retention time on crop leaves and improve utilization efficiency

Pesticides play a very important role in pest control and plant protection. However, they can be limited by a tendency to cause ecological system damage due to significant losses into the environment. To increase pesticide utilization efficiency, we developed highly leaf-adhesive avermectin nanocapsules (Av-pH-cat@CS) with pH-responsive controlled release properties. The Av-pH-cat@CS nanocapsules displayed good thermal stability and photostability in response to UV light irradiation. The Av-pH-cat@CS nanocapsules could be disrupted at low pH and they exhibited excellent controlled release in response to pH, which improved the release of avermectins. In addition, the Av-pH-cat@CS nanocapsules were highly adhesive to crop leaves as a result of strong hydrogen bonding, which prolonged the retention time on crop leaves. The Av-pH-cat@CS nanocapsules with pH-responsive release and strong leaf adhesion improved the control efficacy and enhanced the utilization efficiency. Our findings offer a promising approach to prolonging pesticide duration on crop leaves and improving the utilization efficiency.

Effects of Few-Layer Graphene on the Sexual Reproduction of Seed Plants: An In Vivo Study with Cucurbita pepo L

Products containing graphene-related materials (GRMs) are becoming quite common, raising concerns for environmental safety. GRMs have varying effects on plants, but their impact on the sexual reproduction process is largely unknown. In this study, the effects of few-layer graphene (FLG) and a similarly layered phyllosilicate, muscovite mica (MICA), were tested in vivo on the reproductive structures, i.e., pollen and stigma, of Cucurbita pepo L. ssp. pepo 'greyzini' (summer squash, zucchini). Pollen was exposed to FLG or MICA, after careful physical-chemical characterization, at concentrations of 0.5 and 2 mg of nanomaterial (NM) per g of pollen for up to six hours. Following this, pollen viability was tested. Stigmas were exposed to FLG or MICA for three hours and then analyzed by environmental scanning electron microscopy to verify possible alterations to their surface. Stigmas were then hand-pollinated to verify the effects of the two NMs on pollen adhesion and in vivo pollen germination. FLG and MICA altered neither pollen viability nor the stigmatic surface. However, both NMs equivalently decreased pollen adhesion and in vivo germination compared with untreated stigmas. These effects deserve further attention as they could impact on production of fruits and seeds. Importantly, it was shown that FLG is as safe as a naturally occurring nanomaterial.

Beyond graphene oxide acidity: Novel insights into graphene related materials effects on the sexual reproduction of seed plants

Graphene related materials (GRMs) are currently being used in products and devices of everyday life and this strongly increases the possibility of their ultimate release into the environment as waste items. GRMs have several effects on plants, and graphene oxide (GO) in particular, can affect pollen germination and tube growth due to its acidic properties. Despite the socio-economic importance of sexual reproduction in seed plants, the effect of GRMs on this process is still largely unknown. Here, Corylus avellana L. (common Hazel) pollen was germinated in-vitro with and without 1-100 μg mL^-1 few-layer graphene (FLG), GO and reduced GO (rGO) to identify GRMs effects alternative to the acidification damage caused by GO. At 100 μg mL^-1 both FLG and GO decreased pollen germination, however only GO negatively affected pollen tube growth. Furthermore, GO adsorbed about 10 % of the initial Ca²⁺ from germination media accounting for a further decrease in germination of 13 % at the pH created by GO. In addition, both FLG and GO altered the normal tip-focused reactive oxygen species (ROS) distribution along the pollen tube. The results provided here help to understand GRMs effect on the sexual reproduction of seed plants and to address future in-vivo studies.

Perspectives on plasma-assisted synthesis of N-doped nanoparticles as nanopesticides for pest control in crops

Green plasma-based technology production of N-doped NPs for a new agri-tech revolution in pest control.

Carboxymethyl Chitosan Modified Carbon Nanoparticle for Controlled Emamectin Benzoate Delivery: Improved Solubility, pH-Responsive Release, and Sustainable Pest Control

Environmentally friendly pesticide delivery systems have drawn extensive attention in recent years, and they show great promise in sustainable development of agriculture. We herein report a multifunctional nanoplatform, carboxymethyl chitosan modified carbon nanoparticles (CMC@CNP), as the carrier for emamectin benzoate (EB, a widely used insecticide), and investigate its sustainable antipest activity. EB was loaded on CMC@CNP nanocarrier via simple physisorption process, with a high loading ratio of 55.56%. The EB@CMC@CNP nanoformulation showed improved solubility and dispersion stability in aqueous solution, which is of vital importance to its practical application. Different from free EB, EB@CMC@CNP exhibited pH-responsive controlled release performance, leading to sustained and steady EB release and prolonged persistence time. In addition, the significantly enhanced anti-UV property of EB@CMC@CNP further ensured its antipest activity. Therefore, EB@CMC@CNP exhibited superior pest control performance than free EB. In consideration of its low cost, easy preparation, free of organic solution, and enhanced bioactivity, we expect, CMC@CNP will have a brilliant future in pest control and green agriculture.