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<p>Overall GoalThe overall goal of this proposal is to investigate the interactions between AgNPs and leafy vegetables using SERS mapping to understand the physical and molecular mechanisms AgNPs contaminating fresh produce. This is important for the long-term goal of maintaining the safety and sustainability of agriculture and food system.Objectives are:</p><p>1. Preparation and characterization of AgNPs with different sizes, shapes, and surface modifications.</p><p>2. In vitro characterization of plant biomolecules on AgNPs using SERS.</p><p>3. Identification, quantification, and characterization of AgNPs attachment on and penetration into leaves via surface spray using SERS mapping.</p><p>4. Identification, quantification, and characterization of AgNPs distribution in plant tissues and their fate via root-to-shoot exposure using SERS mapping.</p>
<p>In the proposed study, AgNPs with different sizes, shapes, and surface modifications will be prepared and characterized. Major plant biomolecules such as chlorophyll, cellulose, lipids, proteins, and nucleic acids will be either extracted from plants or purchased. Their interactions with the AgNPs will be characterized by SERS in vitro, which can serve as references for the in vivo study. Two leafy vegetables (spinach and lettuce) will be used as the model plants because they are highly associated with the other food safety problem, i.e. food pathogens. Two contamination routes, surface spray and root-to-shoot exposure will be applied for studying NP attachment and internalization. For studying NP attachment and penetration, surface spray of AgNPs will be applied to mimic the situations of spraying NP containing pesticides or irrigating NP contaminated water. SERS mapping will be used to quantify and characterize the NPs on and in leaves. We will also evaluate the impact of postharvest washing on surface attached AgNPs. For studying NP internalization and fate, we will use the root-to-shoot exposure in a hydroponic system and a soil system. SERS mapping will be used to quantify and characterize the NPs on roots and in leaves. Results will be validated using HRTEM for observing mineral lattice and TEM coupled with electron diffraction for identifying mineral phase. Results from AgNPs with different sizes, shapes, and surface modifications, as well as two plants in two growing systems will be statistically compared.</p>