Nanoscale sulfur can be a multifunctional agricultural amendment to enhance crop nutrition and suppress disease. Pristine (nS) and stearic acid coated (cS) sulfur nanoparticles were added to soil planted with tomatoes (Solanum lycopersicum) at 200 mg/L soil and infested with Fusarium oxysporum. Bulk sulfur, ionic sulfate, and healthy controls were included. Orthogonal end points were measured in two greenhouse experiments, including agronomic and photosynthetic parameters, disease severity/suppression, mechanistic biochemical and molecular end points including the time-dependent expression of 13 genes related to two S bioassimilation and pathogenesis-response, and metabolomic profiles. Disease reduced the plant biomass by up to 87%, but nS and cS amendment significantly reduced disease as determined by area-under-the-disease-progress curve by 54 and 56%, respectively. An increase in planta S accumulation was evident, with size-specific translocation ratios suggesting different uptake mechanisms. In vivo two-photon microscopy and time-dependent gene expression revealed a nanoscale-specific elemental S bioassimilation pathway within the plant that is separate from traditional sulfate accumulation. These findings correlate well with time-dependent metabolomic profiling, which exhibited increased disease resistance and plant immunity related metabolites only with nanoscale treatment. The linked gene expression and metabolomics data demonstrate a time-sensitive physiological window where nanoscale stimulation of plant immunity will be effective. These findings provide mechanistic understandings of nonmetal nanomaterial-based suppression of plant disease and significantly advance sustainable nanoenabled agricultural strategies to increase food production.

We report the structural chemistry and optical properties of tin (Sn)mixed gallium oxide (Ga 2 O 3 ) compounds, where the interfacial phase modulationinduced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga 2 O 3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga 2 O 3 compounds (Ga 2−2x Sn x O 3 , 0.00 ≤ x ≤ 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x ≤ 0.10). The XRD analyses indicate the SnO 2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (E g ), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25−0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO 2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar-and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x ≥ 0.15), Sn was found to be insoluble, which can be attributed to Ga 2 O 3 and SnO 2 possessing different formation enthalpies and cation (Ga 3+ and Sn 4+ ) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.

The interaction of engineered nanoparticles with plant tissues is still not well understood. There is a lack of information about the effects of curing (postharvest treatment) and lignin content on copper uptake by sweetpotato roots exposed to copper-based nanopesticides. In this study, Beauregard-14 (lower lignin) and Covington (higher lignin) varieties were exposed to CuO nanoparticles (nCuO), bulk CuO (bCuO), and CuCl at 0, 25, 75, and 125 mg/L. Cured and uncured roots were submerged into copper suspensions/solutions for 30 min. Subsequently, root segments were sliced for imaging with a 2-photon microscope, while other root portions were severed into periderm, cortex, perimedulla, and medulla. They were individually digested and analyzed for Cu content by inductively coupled plasma-optical emission spectroscopy. Microscopy images showed higher fluorescence in periderm and cortex of roots exposed to nCuO, compared with bCuO. At 25 mg/L, only bCuO showed higher Cu concentration in the periderm and cortex of Beauregard-14 (2049 mg/kg and 76 mg/kg before curing; 6769 mg/kg and 354 mg/kg after curing, respectively) and in cortex of Covington (692 mg/kg before curing and 110 mg/kg after curing) compared with controls ( p ≤ 0.05). In medulla, the most internal tissue, only Beauregard-14 exposed to 125 mg bCuO/L showed significantly ( p ≤ 0.05) more Cu before curing (17 mg/kg) and after curing (28 mg/kg), compared with control. This research has shown that the 2-photon microscope can be used to determine CuO particles in nondyed plant tissues. The lack of Cu increase in perimedulla and medulla, even in roots exposed to high CuO concentrations (125 mg/L), suggests that nCuO may represent a good alternative to protect and increase the shelf life of sweetpotato roots, without exposing consumers to excess Cu.

Orthogonal techniques were used to track manganese nanoparticles (MnNPs) in Capsicum annuum L. leaf tissue and cell compartments and subsequently to explain the mechanism of uptake, translocation, and cellular interaction. C. annuum L was cultivated and foliarly exposed to MnNPs (100 mg/ L, 50 mL/per leaf) before analysis by using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) as well as dark-field hyperspectral and two-photon microscopy. We visualized the internalization of MnNP aggregates from the leaf surface and observed particle accumulation in the leaf cuticle and epidermis as well as spongy mesophyll and guard cells. These techniques enabled a description of how MnNPs cross different plant tissues as well as selectively accumulate and translocate in specific cells. We also imaged abundant fluorescent vesicles and vacuoles containing MnNPs, indicating likely induction of autophagy processes in C. annuum L., which is the bio-response upon storing or transforming the particles. These findings highlight the importance of utilizing orthogonal techniques to characterize nanoscale material fate and distribution with complex biological matrices and demonstrate that such an approach offers a significant mechanistic understanding that can inform both risk assessment and efforts aimed at applying nanotechnology to agriculture.

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