Colloidal suspensions are used in a variety of products, such as personal care products and drug delivery systems, as an antimicrobial agent. However, the full extent of the anti-pathogenic potential of metal-based nanoparticle systems has yet to be defined. In this study, a suite of zero-valent metal colloids was synthesized, characterized, and evaluated as pesticidal and bactericidal agents against the uncurable vector-borne citrus greening disease spread by the Asian citrus psyllid (Diaphorina citri) which carries the bacterial pathogen (Candidatus Liberibacter asiaticus). The formation of improperly developed fruits causes decreased productivity of citrus farms. Silver, zinc, manganese, and copper colloids were synthesized; surface functionalized with positive (cetyltrimethylammonium bromide), negative (citric acid), or neutral (polyvinylpyrrolidone) charged ligands; and then characterized for stability using dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Ultraviolet-Visible-Infrared spectroscopy were performed to measure the absorbance & transmission peaks and characterize surface functional groups. In general, negatively-charged colloids were the most stable (in terms of least aggregation) over time (up to 3 weeks) and concentration (up to 150 ppm) with a zeta potential of approximately -30 mV and polydispersity index of 0.250. Psyllids were exposed to the colloids using artificial feeding; E. coli (as a surrogate for Liberibacter) were inoculated with the colloids over dose-response; and citrus trees were sprayed with the colloids over repeating applications. Results show that the negatively-charged colloids were the most efficacious as measured by psyllid uptake; E. coli colony deformation; and permeation through the upper epidermis of citrus leaf. These data sets show that controlling the colloidal stability and inhibiting aggregation tends to produce better results for environmental health studies. This information can further enhance the current knowledge on the application of metal-based colloidal systems in the field of agriculture as a pest or pathogen control tool.

Evaluating the potential of a suite of metal colloids for the treatment of pathogenic diseases: Case study for citrus greening disease

2019 Fall National Meeting

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