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1. Inactivation of Legionella Pneumophila-Harbored by Amoebae Using a Nano-Enabled Alternative Technology

   Saleh, N. B.; Kirisits, M. J.; Ayres, C. (November 2019, 2019 ASA, CSSA, and SSSA Annual Meeting)

   Legionella pneumophila is a virulent bacterial pathogen that can cause a severe and deadly form of pneumonia called Legionnaires’ disease. Documented cases of Legionnaires’ disease have been rising since 2000. Risk of infection increases when L. pneumophila are harbored inside free-living amoebae, which are resistant to traditional disinfection processes. The ability of amoebae to phagocytose L. pneumophila allows amoebae to act as ‘Trojan horses’ for pathogen transport. This project aims to extract an unintended benefit from low-intensity microwave (MW) radiation (already found in many homes across economic cross-sections) by employing nanomaterials (e.g., silver, copper oxide, and carbon nanotubes) that are capable of harnessing such radiation and localizing the otherwise dissipated energy. In this alternative technology, we hypothesize that amoebae will be lysed via localized interfacial heating, and the released L. pneumophila will be inactivated subsequently by heat, metal ions (from nanoparticle dissolution), and reactive oxygen species (ROS) produced in the process. Traditionally, inactivation of up to 3-logs of planktonic L. pneumophila with dissolved silver requires hours of contact time. This study reports rapid inactivation (in minutes) of 3-log or higher when the planktonic L. pneumophila is subjected to AgNPs (5 mg/L) and MW radiation (2,450 MHz; 70 W). Ensuing phases of this project will incorporate copper oxide nanoparticles – which are anticipated to increase toxicity akin to copper-silver ionization systems currently employed in hospitals for L. pneumophila control – and enhance inactivation potency with potentially lower microwave radiation input and/or a lower concentration of nanoparticles. Ultimately, the nanomaterials will be immobilized on a plaster of Paris or ceramic surface for flow-through applications for lysing amoebae and inactivating L. pneumophila. 

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2. Synergy between microwave radiation and silver for inactivation of Legionella pneumophila

   Saleh, N. B.; Ayres, C.; Lawler, D. F.; Kirisits, M. J. (July 2020, 1st Virtual Canadian Symposium on Water Quality Research)

   Legionella pneumophila is an opportunistic human pathogen that can cause a severe and deadly form of pneumonia called Legionnaires’ disease. Over the past decade, the number of reported cases of Legionnaires’ disease has quadrupled in the U.S., with 8,000-18,000 hospitalizations per year at a yearly incidence rate of 1.7/100,000. Within the water sector, this public health risk is exacerbated by the proliferation of L. pneumophila in complex biological matrices such as biofilms and within free-living amoebae. Traditional disinfection technologies fail to effectively mitigate this emerging pathogen issue, necessitating development of point-of-use (POU) technologies with high inactivation efficacy. We aim to harness microwave (MW) radiation and take advantage of its synergy with ion-mediated toxicity to effectively inactivate L. pneumophila. In this study, planktonic L. pneumophila cells have been exposed to ionic and nano-particulate silver. While neither treatment alone is effective over a short exposure period, a combined treatment of silver with MW radiation successfully achieves 3-4 log removal within 6 min of irradiation, as shown in Figure 1. Enhanced toxicity was observed when L. pneumophila was pre-exposed to either treatment (i.e., MW heating or silver exposure) prior to exposure to the other; these results suggest that silver ion transport within the cells is facilitated by heat treatment. Data presented here serve as the proof-of-concept toward the development of a L pneumophila inactivation device that harnesses MW radiation and can potentially mitigate this public health risk, even if the cells are protected by amoebae or biofilms. 

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3. Emerging investigator series: linking chemical transformations of silver and silver nanoparticles in the extracellular and intracellular environments to their bio-reactivity

   https://doi.org/10.1039/c9en00710e  

   Minghetti, Matteo; Dudefoi, William; Ma, Qing; Catalano, Jeffrey G. (October 2019, Environmental Science: Nano)

   The fish intestine is an important barrier for environmental toxicants, including metals and metal nanoparticles. Tracking chemical transformation at the interface between the intestinal epithelium and the intestinal lumen can inform us about chemicals' bio-reactivity and toxicity but is challenging due to the lack of appropriate models. To allow for such investigations, a model of the fish intestine derived from rainbow trout ( Oncorhynchus mykiss ), the RTgutGC cell line, was used. Cells were exposed to silver nitrate (AgNO 3 ) or citrate coated silver nanoparticles (cit-AgNPs) in Leibovitz's L-15 medium without amino acids and vitamins (L-15/ex), which allowed the determination of the extracellular silver species using a chemical equilibrium model. X-ray absorption spectroscopy (XAS) was used to track intracellular silver speciation. Cellular toxicity, silver accumulation, and metallothionein (MT) mRNA levels were also measured. Cells accumulated the same concentrations of silver when exposed to equimolar amounts ( i.e. 1, 5 and 10 μM) of AgNO 3 or cit-AgNPs. However, AgNO 3 was shown to be more toxic than cit-AgNPs. Intracellular silver speciation changed over time in both exposure series. After 1 hour, intracellular silver speciation was dominated by chloride complexation in both exposures. After 24 and 72 hours of exposure to cit-AgNPs, ∼7% of silver was complexed to cysteine, whereas the remaining silver was AgNPs. In cells exposed to AgNO 3 for 72 hours, 97% of Ag was complexed to cysteine. A significant increase, compared to controls, in metallothionein mRNA levels at 24 and 72 hours of exposure to AgNO 3 and cit-AgNPs can explain the formation of Ag–cysteine complexes. In summary, these data show that silver chloride species are bioavailable and that complexation to cysteine scavenges intracellular dissolved silver ions, thus preventing toxicity. Silver nanoparticles present a similar but attenuated toxic response to AgNO 3 . Thus, at least in acute exposures, existing risk assessment for dissolved silver species could be protective for nanosilver. 

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4. Understanding the Mechanism of Star-Block Copolymers as Nanoreactors for Synthesis of Well-Defined Silver Nanoparticles

   Zhu, Albert; Li, Qiong; Chen, Xiaoyi (August 2018, Journal of emerging investigators)

   Facile and large-scale synthesis of well-defined, thermally stable silver nanoparticles protected by polymer brushes for use in practical applications is still a challenge. Recent work has reported a nanoreactor approach that can be used to synthesize these silver nanoparticles. This approach uses amphiphilic star-block copolymers, which have a hydrophilic core surrounded by a hydrophobic exterior. These polymers thus can serve as the nanoreactors. In this study, we hypothesize that the local high concentration of silver ions in the inner hydrophilic cores of these star-block copolymers facilitates the nucleation and subsequent growth of silver nanoparticles. When all silver nanoparticles nucleate from the cores of the star-block copolymers in solution, the particle size can be controlled by the core size of the polymer. To test this hypothesis, a polyisoprene-b-poly(p-tert-butylstyrene) (PI-b-PtBS) star-block copolymer was functionalized with carboxylic acid groups using a high-efficiency, photo-initiated thiol-ene click reaction. We characterized this modified polymer using proton nuclear magnetic resonance spectroscopy, and the results indicated that ~60% of the double bonds in the polyisoprene block were successfully functionalized with carboxylic acid groups. When silver ions were added to a solution of these functionalized star-block copolymers, the negatively charged carboxylic acid groups would attract the positively charged silver ions. Subsequent reduction of these Ag+ by a tert-butylamine-borane complex at room temperature produced nanosized silver particles. However, transmission electron microscopy images showed that a significant amount of relatively large silver nanoparticles grew outside the star-block copolymer nanoreactors. 

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5. A reaction mechanism for plasma electrolysis of AgNO ₃ forming silver nanoclusters and nanoparticles

   https://doi.org/10.1063/5.0127568  

   Raisanen, Astrid L.; Mueller, Chelsea M.; Chaudhuri, Subhajyoti; Schatz, George C.; Kushner, Mark J. (November 2022, Journal of Applied Physics)

   In plasma-driven solution electrolysis (PDSE), gas-phase plasma-produced species interact with an electrolytic solution to produce, for example, nanoparticles. An atmospheric pressure plasma jet (APPJ) directed onto a liquid solution containing a metallic salt will promote reduction of metallic ions in solution, generating metallic clusters that nucleate to form nanoparticles. In this article, results from a computational investigation are discussed of a PDSE process in which a radio-frequency APPJ sustained in helium impinges on a silver nitrate solution, resulting in growth of silver nanoparticles. A reaction mechanism was developed and implemented in a global plasma chemistry model to predict nanoparticle growth. To develop the reaction mechanism, density functional theory was used to generate probable silver growth pathways up to Ag 9 . Neutral clusters larger than Ag 9 were classified as nanoparticles. Kinetic reaction rate coefficients for thermodynamically favorable growth pathways were estimated based on an existing, empirically determined base reaction mechanism for smaller Ag particle interactions. These rates were used in conjunction with diffusion-controlled reaction rate coefficients that were calculated for other Ag species. The role of anions in reduction of Ag n ions in forming nanoparticles is also discussed. Oxygen containing impurities or admixtures to the helium, air entrainment into the APPJ, and dissociation of saturated water vapor above the solution can produce additional reactive oxygen species in solution, resulting in the production of anions and [Formula: see text] in particular. For a given molarity, delivering a sufficient fluence of reducing species will produce similar nanoparticle densities and sizes for all applied power levels. Comparisons are made to alternate models for nanoparticle formation, including charged nanoparticles and use of direct current plasmas. 

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