Multidimensional response of dopamine nano-system for on-demand fungicides delivery: Reduced toxicity and synergistic antibacterial effects

Pesticides play an irreplaceable role in agricultural production. Pesticides are commonly used to control plant diseases and thereby increase crop yield. The use of pesticides to control pests and pathogens can increase the total yield by 30 %, however, the effective utilization rate of pesticides (including herbicides, insecticides, fungicides, and other agrochemicals) in the application process is extremely low. 90 % of pesticides are lost due to spray drift, tumble, and rain leaching, or degraded due to light, temperature, and microorganisms, and the actual utilization rate of pesticides used in biological targets is less than 0.1 %. The loss of deviation from the target is the key problem of the inefficiency of traditional pesticide preparations. Due to the low actual utilization rate and the huge cost of pesticide application, the excessive use of pesticides in pest control will cause pollution of the ecological environment (including air, water, and soil) and pesticide residues in agricultural products, which will eventually pose a serious threat to public health. Therefore, improving the bioavailability of existing fungicides can not only save a lot of economic costs but also minimize the impact of fungicides on the environment.

In recent years, nanotechnology has shown good prospects in improving the effectiveness and safety of pesticides. Nano-systems can significantly improve the bioavailability and effectiveness of pesticides by delivering pesticides to pests and pathogens. The nano-pesticides of mesoporous silica (MoS2@MSN@CDP) synthesized by Dong et al. can realize the controlled release of pesticides to graded biological targets through the multidimensional stimulation of pH, α-amylase, epidermal wax and sunlight, and improve the bioavailability of pesticides; Huang et al. reported that the synthesized pH-responsive nano-pesticides by using UiO-66-NH2 and sodium lignosulfonate can protect rice from pests for up to 42 days, thus prolonging the pesticide utilization time. Moreover, the use of nano-pesticides can overcome the disadvantages of traditional pesticides, such as ultraviolet degradation, and achieve the effect of the original traditional pesticide with fewer pesticides, greatly reducing the economic cost. Zhao Ming et al. prepared the nano pesticide AVM@CS-SS-Zein with pH/ redox response, and its photostability was 6 times higher than that of AVM, which significantly slowed down the degradation rate of AVM under ultraviolet irradiation. At the same time, compared with traditional pesticides, nano-pesticides can stay on crops for a longer time, and also avoid environmental pollution caused by pesticide loss. Luo et al. used polyethylene glycol and 4,4-methylene diphenyl diisocyanate to prepare nanogels to load pesticides. After foliar spraying, the foliar flat state of nanogels increased the foliar protection area by 2.21 times and improved the pesticide exposure area and target contact efficiency. Furthermore, the flexibility and viscosity of nanogels improved the washing resistance and retention rate of pesticides by about 80 times under continuous washing. Therefore, nano-pesticides provide a feasible strategy for green and sustainable agriculture.

Sclerotinia sclerotiorum is a destructive ascomycete that harms crops and vegetables. It can parasitize more than 600 kinds of plants such as Cruciferae, Solanaceae, Compositae, Amaranthaceae, and Leguminosae, causing huge economic losses. Prochloraz (Pro), a major fungicide used for the control of S. sclerotiorum, significantly reduces its efficacy, utilization, and duration due to drawbacks such as instability under ultraviolet (UV) irradiation and nonsystemic properties. MPDA is a natural polymer inspired by mussels with good biological safety and anti-ultraviolet performance, so it could be used to improve the use of Pro. At the same time, as a new type of functional nanomaterial, MPDA nanoparticles have been proven to have a photothermal conversion efficiency of 40 %, which is much higher than the widely used gold nanorods. As an ideal photothermal agent, MPDA has been used in photothermal therapy and near-infrared controlled release systems. As a self-assembled MPDA in alkaline environment, it can destroy some plant fungi that depend on acidic environment, inhibit the growth of plant fungi, and act as an antifungal agent. In addition, polydopamine itself has a photothermal antibacterial function. In particular, MPDA nanoparticles also have the advantages of low cost and easy preparation, which have great practical application potential.

In this study, mesoporous poly-dopamine (MPDA) was used as the carrier loaded with prochloraz (Pro), and the host–guest complex of β-cyclodextrin (β-CD) and benzimidazole (BIZ) was used as the capping agent of MPDA, and a multi-dimensional responsive poly-dopamine nano-pesticides (Pro@MPDA-BIZ@β-CD) was constructed for the intelligent synergistic control (Scheme 1). Pro@MPDA-BIZ@β-CD can form hydrogen bonds with fatty components on plant leaves, enhance the wettability of nano-preparations, reduce the loss of fungicides caused by rainwater scouring, and improve the utilization rate of fungicides. In the environment of non-bacterial infection, Pro@MPDA-BIZ@β-CD releases pesticide Pro through near-infrared response, which plays a role in preventing plant pathogens. When plants are infected by pathogens such as Sclerotinia sclerotiorum, Sclerotinia sclerotiorum releases oxalic acid to enhance its virulence, while Pro@MPDA-BIZ@β-CD releases Pro in response to acidic microenvironment. At the same time, the nano-poly-dopamine will decompose and consume hydrogen ions under acidic conditions, which will weaken the toxicity of Sclerotinia sclerotiorum and achieve the synergistic antibacterial effects. Therefore, PMBD is expected to provide a feasible strategy for green pesticides.

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