In modern agriculture, pesticides are an important means of reducing plant diseases and pests and improving agricultural production efficiency. However, currently most chemically synthesized pesticides suffer from issues such as biological toxicity, drug resistance, and environmental hazards, and the effective utilization rate of traditional pesticide formulations is relatively low. In order to solve these problems, it is urgent to introduce new and efficient plant disease and pest control technologies to reduce the abuse of chemical pesticides and promote sustainable agricultural development.
In recent years, the development of nanomaterials and related technologies has opened up new avenues for plant disease and pest control. Their unique surface properties and small size effects, as well as novel physical and chemical properties, help overcome many inherent limitations of existing pesticide products. Among various types of nanomaterials, nano silica has attracted widespread attention due to its large specific surface area, good stability, easy surface modification, and good biocompatibility.
This article summarizes the synthesis methods of nano silica and its application in plant disease and pest control, based on recent research progress at home and abroad. It also looks forward to the challenges it faces and future development prospects, aiming to provide theoretical basis for the application of nano silica in plant disease and pest control.

Ⅰ.The synthesis method of nano silica
The traditional synthesis methods of nano silica are mainly divided into physical and chemical methods, which have the main disadvantages of high cost and the need to use toxic and harmful chemicals, which can bring various biological and environmental risks. The biosynthetic method has the characteristics of low cost, low energy consumption, and environmental friendliness, gradually becoming an alternative to physical and chemical synthesis methods.
1. Physical and chemical synthesis of nano silica
The physical synthesis method of nano silica is generally achieved by mechanically crushing large particles of silica using high-energy ball milling or ultrasonic shot peening techniques. The advantages of physically preparing nano silica are simple production process and high yield, but there are disadvantages such as high energy consumption, poor particle spheroidization, and uneven particle size distribution.
Chemical synthesis is the most widely used synthesis method of nano silica at present, mainly including reverse microemulsion method, chemical vapor condensation method and sol gel method. The reverse microemulsion method mostly uses ethyl silicate as the precursor, mixing oil phase, water phase, surfactant and additives to form a water in oil reverse micelle system, which promotes the hydrolysis and condensation of ethyl silicate to form silica. The advantage of this method is that it is easy to regulate and modify nanoparticles, but the disadvantage is high cost and difficulty in removing organic solvents.
The chemical vapor phase condensation method mainly utilizes the hydrolysis and condensation reaction of hydrogen and oxygen with silicon tetrachloride at high temperature to synthesize silica nanoparticles. The advantages of this method are easy operation, simple process, and less pollution, but the disadvantage is that it is difficult to control the size and morphology of the nanoparticles. The sol gel method is mainly to synthesize silica nanoparticles through aging, gel, heating and other steps, using silanolate or sodium silicate as precursor, hydrolysis and condensation to form sol in the presence of acid/base catalyst. The advantage of this method is that the process is easy to control, but the disadvantage is that the raw materials are expensive and the preparation time is long.
2. Biological synthesis of nano silica
The biosynthesis methods of nano silica mainly include the following: using biological cells or their extracts as reducing agents and capping agents to produce nano silica; Preparation of nano silica using natural biomaterials as precursors; Utilizing the biological functions of peptides to mediate the formation of silica. At present, the bioreactors and end capping agents used for producing nano silica mainly include bacteria, fungi, algae, and plant extracts (such as proteins, amino acids, carbohydrates, alkaloids, terpenes, tannins, saponins, phenolic compounds, etc.). Specific reductases in biological cells or their extracts can reduce silanol salts or silicates to silica, and then biomolecules use functional groups such as hydroxyl, carboxyl, and amide to bind with silica, acting as end capping agents around nanoparticles, improving particle stability and biocompatibility.
Zamani et al. synthesized nano silica using sodium silicate as a precursor and Saccharomyces cerevisiae, resulting in spherical amorphous nano silica particles with a size of 40-70 nm. Natesan et al. synthesized silica nanoparticles using Pseudomonas fluorescens, Trichoderma atroviride, and Streptomyces griseus, and conducted toxicity testing on zebrafish. The results showed that the synthesized silica nanoparticles had good biocompatibility.
In order to improve cost-effectiveness, some researchers use plant residues from agriculture and industry as inexpensive precursor materials for the synthesis of nano silica. According to reports, residues of monocotyledonous plants such as sorghum, rice, wheat, and corn contain up to 90% by mass of silica, while common agricultural or industrial waste such as bamboo leaf ash and sugarcane bagasse also contain over 50% by mass of silica. Mor et al. synthesized porous spherical silica particles with an average diameter of 10-15 nm using rice husk ash as a precursor, achieving a purity of up to 98.9%.
Rangaraj et al. synthesized high-purity amorphous silica nanoparticles with a diameter of 10-60 nm using bamboo leaf ash as raw material, and conducted toxicity tests on MG-63 animal cell lines, proving that the biosynthetic nano silica had no significant cytotoxicity at a mass concentration below 125 mg/L. In nature, some animals and plants can form natural silica structures in their bodies, known as biogenic silicification. With a deeper understanding of the mechanism of biological silicification, researchers have discovered key peptides that mediate the precipitation of silica in living organisms.

Kroger et al. discovered a group of proteins with silica affinity from the siliceous shell of marine diatom Cylindrotheca fusiformes and named them Silaffin. The R5 peptide (SSKKSGSYSGSKKRRIL) found in Silaffin is a repeating unit rich in serine and lysine residues, which can mediate silica condensation to synthesize nano silica under neutral pH conditions. Based on the biomimetic silicification of R5 peptide, some researchers have utilized the R5 domain to construct fusion proteins and prepare nano silica composite materials with different structures and functions. For example, Wong et al. fused the spider silk protein domain with R5, and the fusion protein can act as a template for silica condensation through self-assembly during biomimetic silicification, thereby generating composite materials in the form of films and fibers. Similarly, Li et al. used a fusion protein of amyloid protein CsgA and R5 as an in-situ silicified scaffold to construct a self-supporting porous structure composite material.
Compared with physical and chemical synthesis methods, the biosynthesis of nano silica has many advantages and has better application value in plant disease and pest control. Firstly, the biosynthetic method of nano silica can avoid the introduction of highly toxic organic reagents, and can utilize inexpensive raw materials such as plant residues as precursors, making it a green, environmentally friendly, and economically feasible approach. Secondly, biomolecules involved in the biosynthesis process contribute to enhancing the biocompatibility of nanoparticles and improving their ecological and environmental benefits. In addition, biosynthetic methods can also use biological molecules such as peptides as silicification templates to simulate the ordered multi-level porous structure of natural biological silica, achieving precise customization of material properties and functions.

Ⅱ.Application of nano silica in pest and disease control
At present, the application of nano silica in plant pest control mainly includes the following ways: firstly, using nano silica as an insecticidal active ingredient directly for pest control; Secondly, using nano silica as a biostimulant to confer resistance to plant pathogens; Thirdly, using nano silica as a carrier for pesticide active ingredients to construct a nano drug delivery system; Fourthly, nano silica is used as a nucleic acid carrier for the delivery of genetic materials such as DNA and RNA.
1. Silicon dioxide nanoparticles as insecticidal active ingredients
Silicon dioxide nanoparticles have extensive insecticidal activity and have been used as nano pesticides to control a range of pests. The hypothesis regarding the insecticidal mechanism of nano silica is that when silica nanoparticles are sprayed onto the body walls of pests or their larvae, they will be physically adsorbed by the lipids in the insect's epidermis, which may interfere with the insect's stomata and tracheal contraction, leading to respiratory disorders. It may also cause wear on the protective lipid hydrophilic membrane on the insect's stratum corneum, resulting in dehydration, drying, and death. After entering the body of herbivorous pests, nano silica particles may damage the digestive tract through physical abrasion, or generate free radical ions through the breaking of silicon oxygen bonds, disrupting the physiological and metabolic activities of target insects, thereby producing indirect insecticidal effects. Due to the fact that the damage caused by nano silica particles to pests is mainly physical, pests will not develop genetic or physiological resistance to them, which is the advantage of nano silica as an insecticidal active ingredient.
Rouhani et al. found that nano silica has lethal effects on the larvae and adults of Callosobruchus maculatus on cowpea seeds, with LC50 values of 1.03 and 0.68 g/kg, respectively. Thabet et al. used silica nanoparticles to control Spodoptera littoralis on soybeans, Aphis craccivora and Liriomyza trifoli on broad beans. The experimental results showed that silica nanoparticles had significant lethal effects on all three pests, with the best control effect on Aphis craccivora and Liriomyza trifoli. Elsadany et al. found that silica nanoparticles can effectively prevent and control Tetranychus cucurbitacearum on soybeans, and the mortality rate of mites significantly increases with the increase of nanoparticle concentration.

In addition, the pest control effect of silica nanoparticles is related to the size, morphology, and surface characteristics of the particles. Debnath et al. found that the mortality rate of Sitophilus oryzae treated with silica nanoparticles (15-30 nm) was higher than that of larger silica nanoparticles (100-400 nm), demonstrating that smaller sized nanoparticles have higher insecticidal efficacy. Ayoub et al. synthesized silica nanoparticles with different morphologies and structures using different surfactants as templates. They exhibited varying levels of insect toxicity and metabolic activity disruption, demonstrating that changes in the morphology and structure of silica nanoparticles can affect their insecticidal activity.
Debnath et al. found that silica nanoparticles coated with 3-mercaptopropyl triethoxysilane had better control effects on Spodoptera litura larvae than silica nanoparticles coated with hexamethyldisilazane, proving that surface functionalization modification can affect the insecticidal effect of silica nanoparticles.

2. Silicon dioxide nanoparticles as biostimulants
After applying nano silica to plants, it can penetrate the cell wall of plant roots, diffuse in the intercellular filaments, and be transported to the aboveground parts of plants such as stems and leaves in different coagulation states (such as phytoliths and amorphous silica deposits) through the xylem. It also acts as a biological stimulant to induce the plant's systemic defense response, endowing the plant with resistance to pathogens. The principle of nano silica endowing plant pathogens with resistance includes two aspects: physical and biochemical mechanisms.
Firstly, after accumulating in different epidermal tissues of plants, nano silica can crosslink with hemicellulose in the cell wall to form a silica double stratum corneum complex, which serves as a physical barrier to prevent pathogen invasion. In addition, nano silica enhances the biochemical resistance of plants to pathogens by activating defense related enzymes such as 1,3-glucanase, peroxidase, chitinase, glutathione reductase, lipoxygenase, polyphenol oxidase, and phenylalanine lyase, promoting the synthesis of antibacterial compounds such as phenols, flavonoids, and diterpenes, or controlling plant hormone signaling pathways such as salicylic acid, jasmonic acid, and ethylene signaling pathways.
According to reports, most crops such as rice, wheat, sugarcane, mango, sorghum, and tomato can reduce the severity of plant diseases after applying nano silica. For example, nano silica has inhibitory effects on several important plant diseases in rice, such as bacterial blight, sheath blight, brown spot disease, leaf blast, stem rot, and grain discoloration.
Nano silica can also inhibit root rot, leaf spot, rust, and powdery mildew in cucumbers, peas, sugarcane, and wheat. In addition, nano silica can also control important plant diseases such as tomato early blight caused by Alternaria solani, mango bacterial root tip necrosis caused by Pseudomonas syringae, and sorghum anthracnose caused by Colletotrichum sublinolum.

3. Nano silica as a pesticide carrier
Nanoparticles can be used as carriers for pesticide active ingredients through adsorption, encapsulation, embedding, and other binding methods, effectively improving the biocontrol effect of pesticides and achieving the goal of reducing application and increasing efficiency. Among various available nanoparticles, silica nanoparticles are one of the most attractive nanocarriers.
Firstly, nano silica has a large specific surface area, which is beneficial for increasing the loading capacity of pesticide active ingredients. Moreover, the insecticidal activity of nano silica itself can exert a synergistic insecticidal effect, thereby improving the insecticidal effect of pesticides.
Secondly, silica nanoparticles can enhance the adsorption of pesticides on certain leaf surfaces and improve pesticide utilization efficiency. Then, the small size effect of the silica nanoparticle carrier makes it easy to pass through the plant cuticle and stomata, promoting the absorption and utilization of pesticides by plants.
In addition, the structure of silica nanoparticles can be easily adjusted through different synthesis processes, such as forming mesoporous silica nanoparticles with a porous structure. This mesoporous silica nanoparticle helps to improve pesticide loading and slow-release performance, and the mesoporous channels are easy to modify, enhancing the flexibility of nanoparticle use.
Song et al. loaded chlorfenapyr onto silica nanoparticles with a size of 50-200 nm and found that the toxicity of chlorfenapyr loaded onto silica nanoparticles to Plutella xylostella was twice that of commercial micrometer sized chlorfenapyr preparations. Zhao et al. found that silica nanoparticles loaded with spirochete exhibited high sedimentation performance on rough cucumber leaf surfaces and could form a runoff resistant protective layer on cucumber leaves, thereby improving pesticide utilization efficiency.
Xu et al. loaded pyranoside onto silica nanoparticles and found that the nanocarrier promoted the absorption and transport of pesticides by cucumbers, and the smaller the particle size, the higher the transport efficiency.
Gao et al. used hollow mesoporous silica nanoparticles capped with hydroxypropyl cellulose as a carrier for pyraclostrobin, and found that the nanocarrier can significantly improve the photostability of pyraclostrobin, and can quickly release encapsulated pyraclostrobin in response to cellulase or low pH environments.
Abdelrahman et al. loaded prochlorpene onto mesoporous silica and coated the particle surface with pectin as a gating system. They found that the nanocarrier could respond to pectinase to release prochlorpene, exhibiting significant and persistent antifungal effects against Magnaporthe oryzae, and had good absorption and transport properties in rice plants.

4. Nano silica as a nucleic acid carrier
There are two main directions for the application of nano silica as a nucleic acid carrier in plant disease and pest control.
Firstly, utilizing nano silica loaded DNA to promote genetic transformation and recombinant expression of target genes in plants;
Secondly, utilizing nano silica loaded dsRNA to induce RNA interference. Using plant genetic engineering to improve crop varieties is one of the popular research directions for enhancing crop disease and pest resistance.
However, traditional plant genetic transformation methods such as Agrobacterium mediated and gene gun methods have limitations such as narrow host applicability and low transformation efficiency. Nanoparticles are a novel gene carrier in plant genetic engineering, which can transport DNA into plant cells through the cell wall without external assistance, and then release it in specific areas. The porous structure of mesoporous silica nanoparticles helps to load DNA inside the particles, thereby protecting them from degradation by nucleases and accurately transferring DNA to plants for instantaneous or stable transformation.
Torney et al. first utilized mesoporous silica nanoparticles with a pore size of 3 nm as a carrier for green fluorescent protein genes, and covered the mesoporous channels with gold nanoparticles as a capping agent, successfully delivering DNA and chemicals together into tobacco leaf cells.
Hajiahmadi et al. used mesoporous silica nanoparticles with a size of 40 nm to transfer plasmids containing the B.t. toxin protein gene CryIAb into early maturing tomato fruits, resulting in recombinant expression of CryIAb protein in tomato plants, thereby enhancing the resistance of transgenic plants to tomato leaf miner.
RNA interference (RNAi) is a type of post transcriptional gene silencing induced by double stranded RNA (dsRNA). When dsRNA is delivered to pathogenic microorganisms or pests, it can silence and disable target genes, ultimately inhibiting pathogen growth and development or enhancing host plant resistance to pests and diseases. The main obstacle to the practical application of RNAi technology is that the stability of RNA is easily affected by changes in UV radiation, RNA enzymes, temperature, and weather in the field environment.
Using nanoparticles as delivery carriers for dsRNA can effectively improve the stability and delivery efficiency of RNA, thereby enhancing the biological control effect of RNAi. Xu et al. used amino functionalized mesoporous silica nanoparticles to deliver dsRNA for silencing the coat protein encoding gene of potato virus Y. The experimental results showed that silica nanoparticles loaded with dsRNA could effectively silence the target gene and protect plants from virus infection for more than 14 days.

Ⅲ.Problem and Prospect
Pesticides are currently the most widely used method for controlling plant diseases and pests, but conventional pesticides often have problems such as low utilization rate, strong resistance, high biological toxicity, and environmental hazards. As a new technology for pest and disease control, nano silica can be used as an insecticidal active ingredient or biostimulant to protect crops from pest and disease invasion, or as a carrier for pesticide active ingredients to improve the insecticidal activity, stability, target adsorption, and slow-release performance of pesticides. In addition, nano silica can also serve as a carrier for nucleic acid delivery, playing a role in new pest control technologies such as plant genetic engineering and RNA interference. Although some progress has been made in the research of nano silica both domestically and internationally, there are still several issues in the practical application of nano silica.
The large-scale production of nano silica poses certain difficulties. The existing chemical and physical synthesis methods for nano silica lack cost and environmental benefits. Although biosynthesis has the potential to overcome the shortcomings of traditional synthesis methods, its synthesis process is relatively complex and requires further establishment of large-scale and standardized production processes. In addition, most of the research on the prevention and control of pests and diseases by nano silica is conducted under laboratory conditions, with overly detailed experimental processes and insufficient consideration of factors such as production equipment, processes, and costs, which limits large-scale production.
The biosafety of nano silica needs to be comprehensively evaluated. Unlike traditional pesticides, the biological toxicity of nano silica is related to parameters such as particle size distribution, morphological structure, surface properties, and drug loading rate of nanoparticles, and cannot be simply evaluated using existing pesticide toxicology standards. In addition, the degradation, transfer, and enrichment of nano silica in natural environments may pose a threat to the survival of non target organisms in the environment, but relevant research is currently insufficient. Therefore, it is necessary to establish a comprehensive set of standards to evaluate the biological toxicity and environmental behavior of nano silica, and to more comprehensively assess its biosafety.
The policies and regulations for the application of nano silica in agriculture need to be improved. At present, countries around the world lack unified policies, regulations, and industry standards for the application of nanotechnology in agriculture. International organizations such as the Food and Agriculture Organization of the United Nations, the Organization for Economic Cooperation and Development, and the European Union have made it a top priority to develop guidelines and regulations suitable for the development of agricultural nanotechnology. At present, there are still some difficulties in the registration of nano silica pesticides in China, such as the lack of formal formulation names, specialized environmental assessment criteria, and national standards for parameters such as particle size. Therefore, accelerating the improvement of policies and regulations related to the evaluation and registration of nano silica is of great significance for promoting the application of nano silica in agriculture.
At present, the application of nano silica in plant disease and pest control is still in its infancy, and most research is only in the laboratory stage, with a certain distance from large-scale practical application. With further research on the production process of nano silica, the establishment of biosafety evaluation standards, and the implementation of relevant policies and regulations, nano silica has the potential to play a huge application value in the field of plant disease and pest control.