Climate change is increasing the severity and length of heat waves. Heat stress limits crop productivity and can make plants more sensitive to other biotic and abiotic stresses. New methods for managing heat stress are needed. Herein, we have developed ∼30 nm diameter poly­(acrylic acid)-block-poly­(N-isopropylacrylamide) (PAA-b-PNIPAm) star polymers with varying block ratios for temperature-programmed release of a model antimicrobial agent (crystal violet, CV) at plant-relevant pH. Hyperspectral-Enhanced Dark field Microscopy was used to investigate star polymer–leaf interactions and route of entrance. The majority of loaded star polymers entered plant leaves through cuticular and epidermis penetration when applied with the adjuvant Silwet L-77. Up to 43 wt % of star polymers (20 μL at 200 mg L–1 polymer concentration) applied onto tomato (Solanum lycopersicum) leaves translocated to other plant compartments (younger and older shoots, stem, and root) over 3 days. Without Silwet L-77, the star polymers penetrated the cuticle, but mainly accumulated at the epidermis cell layer. The degree of the star polymer temperature responsiveness for CV release in vitro in the range of 20 to 40 °C depends on pH and the ratio of the PAA to PNIPAm blocks. Temperature-responsive release of CV was also observed in vivo in tomato leaves. These results underline the potential for PAA-b-PNIPAm star polymers to provide efficient and temperature-programmed delivery of cationic agrochemicals into plants for protection against heat stress.

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Noble metal nanoparticles are promising catalysts in electrochemical reactions, while understanding the relationship between the structure and reactivity of the particles is important to achieve higher efficiency of electrocatalysis, and promote the development of single-molecule electrochemistry. Electrogenerated chemiluminescence (ECL) was employed to image the catalytic oxidation of luminophore at single Au, Pt, and Au-Pt Janus nanoparticles. Compared to the monometal nanoparticles, the Janus particle structure exhibited enhanced ECL intensity and stability, indicating better catalytic efficiency. On the basis of the experimental results and digital simulation, it was concluded that a concentration difference arose at the asymmetric bimetallic interface according to different heterogeneous electron-transfer rate constants at Au and Pt. The fluid slip around the Janus particle enhanced local redox reactions and protected the particle surface from passivation.

We assess the effect of CuO nanoparticle (NP) concentration and soil aging time on the extractability of Cu from a standard sandy soil (Lufa 2.1). The soil was dosed with CuO NPs or Cu(NO3)2 at 10 mg/kg or 100 mg/kg of total added Cu, and then extracted using either 0.01 M CaCl or 0.005 M diethylenetriaminepentaacetic acid (DTPA) (pH 7.6) extraction fluid at selected times over 31 days. For the high dose of CuO NPs, the amount of DTPA-extractable Cu in soil increased from 3 wt % immediately after mixing to 38 wt % after 31 days. In contrast, the extractability of Cu(NO) was highest initially, decreasing with time. The increase in extractability was attributed to dissolution of CuO NPs in the soil. This was confirmed with synchrotron X-ray absorption near edge structure measurements. The CuO NP dissolution kinetics were modeled by a first-order dissolution model. Our findings indicate that dissolution, concentration, and aging time are important factors that influence Cu extractability in CuO NP-amended soil and suggest that a time-dependent series of extractions could be developed as a functional assay to determine the dissolution rate constant.

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