SILVER NANOPARTICLES IN ENVIRONMENTAL AND BIOLOGICAL SYSTEMS: SOURCE, TRANSFORMATION, AND DETECTION

Silver nanoparticles (AgNPs) are the most commonly used nanoparticles in consumer products. Concerns over human exposure to and risk from these particles have resulted in increased interest in novel strategies to detect manufactured AgNPs. This dissertation investigated the feasibility of SERS as a technique for the detection and quantification of manufactured AgNPs in different matrices. By using ferbam as an indicator molecule that binds strongly onto the nanoparticles, AgNPs detection and discrimination were achieved based on the signature SERS response of AgNPs-ferbam complex. AgNPs coated with citrate and polyvinylpirrolidone (PVP) showed strong interactions with ferbam and induced high SERS signals. SERS was effectively applicable for detecting Ag particles ranging from 20 nm to 200 nm, with the highest signal intensity in the 60-100 nm range. To detect AgNPs in complex matrices (commercial antimicrobial products, environmental waters, and biological tissues), different enrichment and purification strategies (centrifugation, filtration, and extraction after hydrophobization) were developed. The findings demonstrate that by coupling with effective sample preparation methods, SERS can serve as a promising analytical platform for studying manufactured AgNPs in complex matrices. Further, SERS was applied to investigate the naturally formed AgNPs in plant root zone. Natural formation of AgNPs is an important pathway that can modify the fate, behavior, and biological availability of Ag+ in the environment. By using SERS and multiple other techniques, we demonstrate the importance of plant roots and associated exudates in mediating the transformation of Ag+ in the presence of sunlight. Morphological changes were observed from 0 h to 24 h with initial cubic AgCl microcrystals (µAgCl) converted to cauliflower-shaped core-shell structures with AgNPs as the shell and µAgCl as the core. We found Cl- in root exudatesplayed an important role in converting Ag+ to AgNPs through the formation of photoreactive µAgCl. Further characterizing the formed AgNPs and monitoring the dynamics using SERS yield important insights into the interaction of AgNPs with biomolecules in root exudates. The discovery of plant root exudate-mediated phototransformation of Ag+ adds new knowledge to our understanding of Ag transformation in plant root zone and will guide the assessment of both exposure and risk in the environment. Silver nanoparticles (AgNPs) are the most commonly used nanoparticles in consumer products. Concerns over human exposure to and risk from these particles have resulted in increased interest in novel strategies to detect manufactured AgNPs. This dissertation investigated the feasibility of SERS as a technique for the detection and quantification of manufactured AgNPs in different matrices. By using ferbam as an indicator molecule that binds strongly onto the nanoparticles, AgNPs detection and discrimination were achieved based on the signature SERS response of AgNPs-ferbam complex. AgNPs coated with citrate and polyvinylpirrolidone (PVP) showed strong interactions with ferbam and induced high SERS signals. SERS was effectively applicable for detecting Ag particles ranging from 20 nm to 200 nm, with the highest signal intensity in the 60-100 nm range. To detect AgNPs in complex matrices (commercial antimicrobial products, environmental waters, and biological tissues), different enrichment and purification strategies (centrifugation, filtration, and extraction after hydrophobization) were developed. The findings demonstrate that by coupling with effective sample preparation methods, SERS can serve as a promising analytical platform for studying manufactured AgNPs in complex matrices. Further, SERS was applied to investigate the naturally formed AgNPs in plant root zone. Natural formation of AgNPs is an important pathway that can modify the fate, behavior, and biological availability of Ag+ in the environment. By using SERS and multiple other techniques, we demonstrate the importance of plant roots and associated exudates in mediating the transformation of Ag+ in the presence of sunlight. Morphological changes were observed from 0 h to 24 h with initial cubic AgCl microcrystals (µAgCl) converted to cauliflower-shaped core-shell structures with AgNPs as the shell and µAgCl as the core. We found Cl- in root exudatesplayed an important role in converting Ag+ to AgNPs through the formation of photoreactive µAgCl. Further characterizing the formed AgNPs and monitoring the dynamics using SERS yield important insights into the interaction of AgNPs with biomolecules in root exudates. The discovery of plant root exudate-mediated phototransformation of Ag+ adds new knowledge to our understanding of Ag transformation in plant root zone and will guide the assessment of both exposure and risk in the environment