NACs (such as NPCs) represent a remarkable advancement in contemporary agricultural practices. Nanostructures are used as carriers for agrochemical AIs ^[1][123]. The utilization of nanotechnology in agrochemicals effectively addresses the limitations associated with traditional agrochemicals, such as limited bioavailability, susceptibility to photolysis, and the potential for organic solvent pollution ^[2][13]. Researchers have conducted an extensive analysis of a large dataset consisting of 36,658 patents and 500 peer-reviewed journal articles, resulting in the identification of two prominent categories of NPCs. Type 1 NPCs consist of metals such as Ag, Cu, and Ti, while Type 2 NPCs involve the utilization of nanocarriers to encapsulate the AIs. These nanocarriers can be composed of various materials such as polymers, clays, and zein nanoparticles (NPs) ^[3][17].

The m-NPCs use metallic nanoparticles as active ingredients, providing numerous advantages compared to conventional chemical pesticides ^[4][130]. They are smaller, usually between a few and 200 nm ^[3][5][17,131]. The presence of multiple active sites for the release of bioactive molecules, ion-exchanging properties, high adsorption ability, efficient surface chemistry, high thermo-stability, and exceptional electronic characteristics in nanotechnology have led to the development of m-NPCs ^[5][6][131,132]. In general, metal formulations are synthesized using metal clusters or ions as nucleation centers which are interconnected by organic ligands. Metal-based encapsulation exhibits advantageous properties such as high surface/volume ratio, voluminous pores, adjustable pore size, efficient surface chemistry, high thermo-stability, and multiple topologies ^[5][131]. These NPCs are effective against a wide range of pests and diseases, but they also have the potential to be toxic to non-target organisms. Recent studies have demonstrated that their utilization shows superior efficacy compared to their non-nanoscale analogues. This advancement has proven to be involved in augmenting agricultural productivity, ensuring the safety of food products, and enhancing their nutritional content ^[3][17]. m-NPCs can act as pesticides by producing reactive oxygen species (ROS), releasing cations, damaging biomolecules, depleting ATP, and interacting with membranes ^[7][133]. A range of metallic and metallic oxide NPs have shown promising sustainable agriculture and antimicrobial applications in vitro against Gram-positive and -negative bacteria. Gold and silver NPs are useful for combating bacteria ^[8][9][15,134] and copper NPs can be used to treat fungal infections in plants ^[9][10][134,135] such as against pathogenic fungi Stachybotrys chartarum and Candida albicans ^[11][136]. The application of Ag NPs is their use as an antibiofilm coating. Additionally, these NPs have demonstrated antimicrobial properties against various microorganisms such as fungi and viruses, including SARS-CoV-2 ^[12][137]. Other metallic oxide NPs, like titanium dioxide (TiO₂), zinc oxide (ZnO), and iron oxide (Fe₂O₃), have antimicrobial and fungicidal properties, making them useful for averting plant diseases ^[8][15]. ZnO-NPs have demonstrated enhanced efficacy against a range of microorganisms, including Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus, Sarcina lutea, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, Pseudomonas vulgaris, Candida albicans, and Aspergillus niger ^[13][138]. Green synthesis of ZnO-NPs led to several morphological and histological abnormalities in Ae. Aegypti third instar larvae ^[14][122]. Some of the different types of m-NPCs are summarized in Table 13.

The nc-NPCs represent a category of NPCs wherein AIs are encapsulated within nanocarriers. The AIs in this type are mainly conventional pesticides, such as atrazine, avermectin, and glyphosate. Nanocarriers can be composed of diverse materials, such as polymers, lipids, and proteins. The utilization of nanocarriers in NPCs presents numerous benefits, such as enhanced solubility, stability, and regulated release of AIs. The application of these agents may enhance the efficacy of NPCs by improving their capacity for permeability and absorption into plant tissues. Therefore, they have demonstrated enhanced action and efficacy of AIs in comparison to conventional formulations, owing to their diminutive dimensions and substantial surface area ^[3][5][17,131]. Recent advancements in biopolymer modification have enabled enhanced control over nanocarriers’ characteristics and their interactions with cargoes and plant tissues. Lignocellulosic-based nanocarriers offer a promising platform for the development of environmentally friendly NPCs due to their non-toxic and biodegradable nature. Tannins and β-glucan are also being studied as potential nanocarriers for AIs ^[15][139]. It has been reported that the tobacco mild green mosaic virus (TMGMV) and other plant viruses can act as nanocarriers for AIs to effectively deliver pesticides to target cells ^[16][17][140,141]. NPCs utilizing nanocarriers possess certain advantages; however, concerns and challenges persist regarding their application. Thorough evaluation of the risks and potential harm to people and the environment is necessary ^[18][142]. Different types of nanocarriers which have been used to encapsulate AIs (type 2 NPCs) are shown in Figure 15.

Silicon’s ability to improve plant tolerance to different stresses has been well established. As a result, silica nanoparticles have been proposed as potential tools for better pest management in agriculture ^[45][169] and later investigated for their potential in delivering pesticidal effects ^[27][151]. Silicon dioxide NPs (SiO₂-NPs) exhibit a porous structure, exceptional surface activity, and notable adsorption properties, rendering them highly suitable for diverse applications, including their potential utilization in nanopesticides (1). This porosity enhances the contact between pesticides and siliceous frameworks, potentially improving their effectiveness by increasing UV-shielding capabilities ^[27][151], and lets them serve as an excellent nanocarriers for different agrochemicals ^[4][130]. They can be used in agriculture in two ways: as direct field application pesticides, killing insects, and as carriers for different herbicides and insecticides due to their ability to enhance the longevity and effectiveness of various commercial pesticides ^[46][170]. However, their efficacy as pesticides may vary depending on their origin and composition. For example, the efficacy of a compound derived from crystalline silica samples was found to be lower in suppressing potato tuber moth when compared to that derived from amorphous silica powders ^[47][171]. Studies have demonstrated that this type of NP can exert toxic effects on non-target organisms. For instance, Galleria mellonella larvae exposed to SiO₂-NPs exhibited a notable reduction in both total hemocyte count and hemocyte viability ^[48][172]. Nanotubes containing aluminosilicate have been found to attach to plant surfaces and insect hair, allowing them to enter the insect body and disrupt its physiological functions. They caused 100% mortality in the cowpea weevil C. maculatus when applied at a rate of 2.06 g/kg. Chlorpyrifos-loaded SiO2-NPs (Ch-SNPs) were found to effectively control R. dominica and T. confusum, with mortality increasing as the concentration of Ch-SNPs increased ^[4][130]. These NPs derived from Alstonia scholaris exhibited increased toxicity against R. dominica, as evidenced by an LC₅₀ value of 0.8 mg/mL and an LC₉₅ value of 1.95 mg/mL. The repellent properties of NPs when combined with the plant oil Ricinus communis also increased against T. castaneum ^[4][130]. Table 3 provides a general overview of some examples of silica nanopesticides and their applications. The specific properties and applications of silica nanopesticides can vary depending on the type of nanoparticle and the target organism.

Nanoemulsion-based pesticide formulations refer to a specific category of pesticide formulations that involve the integration of AIs within a nanoemulsion system. They are colloidal dispersions that consist of extremely small particles, typically within the size range of 20–200 nm. These emulsions are economically cheaper and commonly composed of oil-in-water (O/W type) phases ^[4][49][130,173]. The purpose of these formulations is to mitigate and manage the impact of pests and diseases on crops. They have been specifically developed to optimize efficacy by functioning as a carrier to transport and administer bioactive compounds to the intended pests in agricultural settings ^[49][173]. Their notable benefit is cost-effectiveness due to their high water solubility, allowing them to easily dissolve hydrophilic and lipophilic compounds. Consequently, a reduced amount of AIs and inert material is needed. The improved solubility and absorption of these formulations lead to enhanced efficacy against pathogenic organisms such as bacteria, fungi, and insects ^[49][50][173,174]. This potentially contributes to the reduction of environmental pollution ^[1][123]. In addition, nanoemulsions show excellent storage stability over a wide temperature range (−10 to 55 °C). They have demonstrated their effectiveness in combating various storage pests, including adults and larvae ^[4][130].

SiO₂-NPs are employed as carriers in nanoemulsions, which is an example of utilizing mesoporous SiO₂-NPs as delivery systems for hydrophobic substances such as drugs and pesticides. These SiO₂-NPs improve the stability and efficacy of the nanoemulsion, specifically in delivering AI to pests in agriculture. They, with the aid of SiO₂-NPs, have shown promise in enhancing the delivery and effectiveness of lipid-soluble substances in pesticide formulations ^[50][51][174,175]. Another example is β-cypermethrin, which has been successfully integrated into nanoemulsions through the utilization of different surfactants and oil phases, leading to the formation of stable pesticides exhibiting enhanced characteristics ^[50][174]. Their application in formulations has demonstrated potential for enhancing pest control efficacy, particularly with regard to insects that commonly infest stored grains ^[4][130]. Neem oil-containing nanoemulsions have proven effective against two economically significant agricultural pests: the red flour beetle (Tribolium castaneum) and the rice weevil (Sitophilus oryzae) ^[52][176]. In terms of pest control in particular, nanoemulsions present a promising alternative that can improve safety in human health and environmental aspects with the least amount of harm to the environment and non-targeted organisms ^[52][53][176,177]. Table 13 summarizes the types, composition, effectiveness, and ecological risks of the specified nanoemulsions. Further investigation is required to fully comprehend their potential ecological risks and their impacts on non-target organisms ^[30][154].

PB-NPCs employ polymeric nanoparticles as carriers for active ingredients in pesticide formulations. NPs usually have dimensions ranging from 1 to 1000 nm ^[37][161]. The AIs are encapsulated within these polymers, which can encompass a range of agrochemicals including insecticides, herbicides, and fungicides ^[37][38][161,162]. Polymeric NPs possess biocompatibility, biodegradability, and the ability to undergo chemical surface modification, rendering them highly appealing for pesticide delivery ^[38][162]. NPs possess advantageous characteristics including controlled release of AIs, safeguarding against degradation, and enhanced water solubility ^[37][54][161,178]. Several examples exist of PB-NPCs, which serve as effective polymer nanocarriers. These nanocarriers possess desirable characteristics such as the ability to design intricate pesticide delivery systems with diverse modes of action, biocompatibility, scalability in preparation, and biodegradability ^[22][146]. Pesticide molecules are distributed randomly within a polymer matrix in nanocapsules called polymer micelles, forming a core-shell structure in polymer nanospheres. This serves as a reservoir for encapsulation ^[22][146]. Polycaprolactone (PCL), polyethylene glycol (PEG) and polylactic acid (PLA) are biodegradable polyesters utilized in the fabrication of PB-NPCs. One advantage of them is that they provide the ability to control the release of substances, as well as compatibility with biological systems. PEG is recognized for its capacity to improve the solubility and stability of AIs ^[37][161]. Chitosan, a naturally occurring polymer obtained from chitin, has been widely utilized in NPC formulations due to its abundant availability and inherent properties. It also provides benefits such as biocompatibility, biodegradability, and controlled release of active compounds ^[37][161]. The potential environmental and health impacts of PB-NPCs necessitate comprehensive evaluation and additional research to ensure their safe and effective implementation, despite their promising benefits for sustainable agriculture ^[37][161]. The composition, efficacy, and ecological risks of a few different types of PB-NPCs are summarized in Table 13.

Chit-NPCs have garnered considerable interest in the agricultural sector owing to their distinct characteristics. Chitosan is a linear polysaccharide that is derived from chitin through the process of deacetylation. It is a naturally occurring substance. The material possesses biodegradability, biocompatibility, and non-toxicity, rendering it highly suitable for diverse applications ^[55][179]. Chit-NPCs have been found to exhibit dual functionality in agriculture, serving as both growth enhancers and potent antimicrobial agents against pathogenic fungi and bacteria. They can be developed by utilizing NPs as carriers for existing AIs ^[56][180]. The efficacy of these mechanisms can be augmented by the diminutive dimensions of the chitosan nanoformulations ^[56][180]. Silva et al. (2011) devised chitosan and alginate nanoparticles as carriers for the herbicide paraquat ^[40][164]. This intervention led to a reduction in disease incidence and a simultaneous enhancement in fruit yield ^[3][17]. Chit-NPCs have been used in the production of RNAi-Chit-NPCs (RChit-NPCs) to effectively control forest insect pests ^[57][181]. They can be used in drug delivery systems owing to their mucoadhesive characteristics, positive surface charge, and capacity to disrupt intercellular tight junctions ^[58][182]. Common techniques for the production of Chit-NPCs include ionotropic gelation, microemulsion, emulsification solvent diffusion, and emulsion-based solvent evaporation. Their particle size and surface charge are influenced by several key characteristics, including molecular weight, degree of deacetylation, pH, and chitosan concentration ^[42][166]. Table 13 summarizes the types, composition, effectiveness, and ecological risks of Chit-NPCs.

NCs are a specific class of nanopesticides that encapsulate pesticide AIs within a nanoscale shell. Similar to other NACs, these novel formulations also present many benefits compared to conventional pesticides, augmenting their effectiveness, safety, and ecological sustainability ^[1][3][17,123]. They can be synthesized from diverse materials such as clay minerals (bentonite, smectite, chaolite, and montmorillonite), lipids (triglycerides or waxes), inorganic porous materials, natural polymers (chitosan, cellulose, and polylactide), and synthetic polymers (polylactic acid) ^[1][3][17,123]. The AIs within the NCs can be incorporated into the matrix through either chemical bonding or physical adsorption, employing various techniques. This is an effective strategy to mitigate the loss of efficacy caused by evaporation, degradation, and leaching. Furthermore, it enhances the activity of substances by facilitating improved interactions with various harmful pests ^[1][123]. It shows a 31% increase in efficacy against target organisms and a 43% decrease in toxicity towards non-target organisms ^[59][183]. NCs have the potential to enhance the efficacy of pesticides through improvements in permeability, solubility, stability, and controlled release mechanisms ^[60][2].

In addition, they possess distinctive physicochemical characteristics, including adjustable dimensions, minimal cytotoxicity, and heightened efficacy of encapsulated AIs. Consequently, they can serve as a proficient vehicle for delivering AIs. This phenomenon may result in enhanced absorption by pests and heightened pesticidal efficacy ^[59][183]. Although NCs have numerous advantages, they also present certain potential challenges. Their distinctive physicochemical characteristics, which contribute to their biological impact, may also present unforeseen toxic hazards. To ensure their safe utilization, it is imperative to possess a thorough comprehension of nanoparticle toxicity ^[61][184].

However, the development and optimization of NC formulations is a complex process that necessitates specialized expertise ^[43][167]. The initial cost of NC-based pesticides may be higher compared to conventional formulations, which can be primarily attributed to the expenses involved in registering a novel AI ^[62][185]. Liposome NCs have the ability to encapsulate diverse pesticide AIs, exhibiting notable effectiveness against a range of organisms including insects, fungi, bacteria, and other pests ^[63][186]. Polymeric NCs can be synthesized using a diverse range of polymers, including both synthetic and natural polymers. They offer controlled release properties and can be modified for precise delivery ^[43][62][167,185]. Solid lipid nanoparticle (SLNs) NCs are composed of solid lipids, specifically triglycerides or waxes ^[43][62][167,185]. SLN formulations have already proven to be suitable carriers in agriculture ^[64][187]. NPs offer a sustained release mechanism for pesticides, commonly employed for foliar applications ^[43][62][167,185]. The efficacy of NPCs is addressed in Table 13, while an explicit discussion on ecological risks is absent in the literature. However, they are widely acknowledged for their biocompatibility and biodegradability, indicating a potentially lower ecological impact compared to conventional pesticides ^[1][3][38][17,123,162].

Semiconductor nanoparticles called “quantum dots” and carbon nanotubes are used for the targeted application of pesticides and agricultural chemicals to plants ^[8][15]. Liposomes, which are spherical vesicles made of lipids, are a precise method of delivering pesticides and agrochemicals to plants. Dendrimers in the shape of trees are effective at delivering pesticide AIs to crops with pinpoint accuracy. Nanocapsules, which are comprised of extremely small particles of polymer, can efficiently deliver agricultural chemicals to plants. Water, oil, and surfactants form nanoemulsions, which can be used to selectively deliver agricultural chemicals to plants ^[8][65][1,15].

The efficacy of nano-agrochemicals in agricultural applications has been substantiated by their demonstrated ability to yield desired outcomes. They are employed to enhance the efficacy of pesticides and herbicides relative to their conventional counterparts, with the aim of enhancing disease management and pest control. They have shown to be up to ten times more toxic to their target pest than their non-nano analogues and their usage can reduce environmental contamination by 20–30% ^[66][188]. NPCs and NHCs are very effective in agriculture for nutrient and pest management due to their efficiency, high penetration ability into plant tissues or insect cuticles, and surface area due to their nano-size. These particles are environmentally friendly and effectively mitigate environmental pollution ^[67][189].

The success of these innovative agrochemicals can be attributed to a multitude of factors, such as the nanomaterial or encapsulation technique used, the pests or diseases they are designed to combat, the mechanisms underlying their functionality, and the methods by which they are applied. They demonstrate superior performance compared to conventional pesticides in various aspects ^[2][13]. Some examples of desirable characteristics in an agrochemical include the following: the ability to selectively target specific plant parts or pests for the delivery of active ingredients while minimizing off-target effects; the reduction of pesticide loss due to runoff or degradation ^[1][3][17,123]; the reduction of pesticide toxicity to non-target organisms; and the demonstration of synergistic effects when used in conjunction with other agrochemicals ^[2][68][13,190]. However, different formulations may display different functionalities, and researchers are currently investigating this. NPs’ stability, environmental interactions, and compatibility with different crop varieties must all be carefully evaluated. NACs need to be tested in the field to prove their efficacy and checked for safety before they can be used widely in agriculture ^[2][13]. The proposed antimicrobial mechanism for metal NPs is shown diagrammatically in Figure 26 ^[69][191]. It is important to remember that research is still being done to determine whether or not NACs are effective, and that different formulations may produce different results. It is critical to consider nanoparticle stability, environmental factors, and crop compatibility.

Ecological risks are defined as the effect and behavior of NACs on communities, populations, and ecosystems as compared to the other contaminants present in the environment. The ability of NPs to retain their properties, reactivity, and particle size when they enter the environment can make them toxic to the targeted organisms as well as non-targeted species ^[70][71][192,193]. As mentioned earlier, NACs have shown different effects on field crops as compared to conventional products ^[71][193]. Due to the excessive usage of NACs in the environment, their ecological risks have become a major concern in the last few years. The toxicity of NPs and NACs can be determined by their shape, size, and biodegradability. NPs can be classified on the basis of their shape and biodegradability into four categories: (i) size < 100 nm and non-biodegradable, (ii) size < 100 nm and biodegradable, (iii) size > 100 nm and biodegradable, (iv) size > 100 nm and non-biodegradable ^[72][194]. Certainly, non-biodegradable products can persist in the body and present enhanced toxicity risks. It is suggested that NPs have compound interactions with microorganisms present in the soil; even the minimum concentration of nanoparticles can disturb a microbial community ^[73][195]. Soil microbes play a very important role in the maintenance of soil ecosystems by performing different activities including nutrient recycling, growth enhancement, decomposition of soil organic matter, disease suppression, etc. Any substance that shows negative effects on microbial populations in soil may disturb the sustainability and quality of soil ^[4][130]. Similarly, a plant-associated community, Bradyrhizobium canariense, was revealed to be significantly sensitive to NPs ^[74][196]. Globally, the applications and safe use of nanoparticles for crop protection and yield enhancement are currently a major concern. It has been found that AgNPs showed some inhibitory effects on the activity of soil exoenzymes which enhance soil’s biochemical processes ^[75][197].

Conducting a comprehensive examination of the environmental fate, toxicity, and long-term consequences associated with their use is imperative prior to their widespread implementation. Regulatory frameworks are of the utmost importance, given their distinctive characteristics, and in adherence to the precautionary principle ^[76][77][198,199]. By adopting sustainable pest control strategies, one can effectively mitigate environmental impacts and reduce reliance on pesticides. Disseminating information regarding the advantages and disadvantages of nano-agrochemical use is crucial to fostering well-informed public discourse and ensuring responsible progress ^[78][200]. The implementation of nanocarriers to deliver pesticides specifically to pests has the potential to mitigate ecological risks and decrease environmental exposure ^[3][17].