Browsing by Subject "Silver nanoparticles"
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Item A molecular biological model describing silver nanoparticle mechanism of toxicity and associated antibiotic resistance(2018-05-04) Chambers, Bryant Allson; Kirisits, Mary Jo; Katz, Lynn E; Saleh, Navid; Hofmann, Hans; Parsek, MatthewControl of microbial growth is key to proper function of engineered systems and human health. Combating biological contamination in engineered processes is complicated due to the limited number of materials that are both able to impede microbial growth and are benign with respect to human and environmental health. Silver nanoparticles (AgNPs) have emerged as a novel biocide, reducing biological fouling in consumer goods and health care materials. Their almost ubiquitous usage is primarily due to their microbial cytotoxicity, limited human toxicity, and their ability to be incorporated into a wide variety of materials. The use of AgNPs is not without challenges; microbial toxicity varies by exposure methodology, and studies have shown that AgNPs have the potential to disrupt engineered biological processes either as nanoparticles or through the dissolution of aqueous silver (Ag([subscript aq])). The use of AgNPs is further complicated by their mechanisms of action; there is significant overlap of their biological targets with the targets of antibiotics. Thus, antibiotic resistance might result from AgNP exposure through the processes of co- and cross-resistance, in which one chemical selects for microbial resistance to a second (unrelated) chemical. In this work, the impact of AgNP aggregation and dissolution on toxicity to Escherichia coli was examined. Data indicate that conditions promoting high fractal dimension promote greater toxicity and induce an oxidative stress response. Subsequent studies on the opportunistic human pathogen Pseudomonas aeruginosa were directed at elucidating the mechanisms of action of AgNPs and the microbial response. Transcriptomic and proteomic studies focused on defining a model of bacterial AgNP interaction and isolated mechanisms of toxicity of AgNPs. Further these data provided the first evidence of AgNP exposure resulting in antibiotic resistance through the expression of multidrug efflux pumps. Transcriptomic data indicated that the stress response systems activated as a result of AgNP exposure were localized to the periplasm while the stress response systems activated as a result of Ag([subscript aq]) exposure were localized to the cytoplasm, which supports a surface attachment model of bacterial AgNP interaction distinct from that of Ag([subscript aq]). Transcriptomic studies revealed that key antibiotic resistance systems, including mexGHI and mexPQ, were stimulated by AgNP exposure. P. aeruginosa cells that were pre-exposed to a sublethal concentration of AgNPs demonstrated increased resistance in subsequent antibiotic challenges, demonstrating that antibiotic resistance can be induced by AgNPs. The findings of this study are an important contribution to our understanding of the impacts of co- and cross-resistance induced by AgNP exposure and will ultimately help inform decisions related to human and environmental healthItem LAMA-produced metal-on-oxide nanoparticles and films(2016-05) Gammage, Michael Drew; Kovar, Desiderio; Becker, Michael F; Keto, John W; Henkelman, Graeme; Fan, DongleiThe capability for the Laser Ablation of Microparticle (LAMA) process for producing unique nanostructured particles and films are studied. The processing parameters are adjusted to create nanostructures that have potential for producing superior properties in two distinct technologically important areas – olefin gas separations and plasmonic films. Two extremes in film nanostructure are targeted; 1) Highly porous metallic films for olefin separation and 2) Dense films for plasmonic optical films. For olefin separations, weak chemisorption of ethylene has been shown to be an important characteristic in the use of metals for the separation of ethylene from ethane. Previously, density functional theory (DFT) has been used to predict the binding energies of various metals and alloys, with Ag having the lowest chemisorption energy amongst the metals and alloys studied. Here non-equilibrium Au/Cu alloys are produced using LAMA and investigated by a combination of DFT calculations and experimental measurements. It is inferred from experiments that the binding energy between a Au/Cu alloy and ethylene is lower than to either of the pure metals Au or Cu, and DFT calculations confirm this results from Au segregation to the particle surface. Implications of this work suggest that it may be possible to further tune the binding energy with ethylene by compositional and morphological control of films produced from Au-surface segregated alloys. LAMA-produced metal-on-oxide nanoparticles (NP) are investigated to determine whether the thermal stability of LAMA-produced nanoparticles can be improved without impacting their chemical reactivity. Investigations before and after heating using the transmission electron microscope show that Ag-on-TiO2 nanostructures exhibit excellent resistance to coarsening at elevated temperatures and that there is no change to the binding energy of the ethylene to Ag. For plasmonic film applications, SiO2 and metal-in-SiO2 films were produced using LAMA and studied. Although dense SiO2 films were not produced, it was demonstrated that it was possible to measure the plasmonic absorption peaks of metal NPs embedded in SiO2 films. This opens up a new possibility for the investigation of the plasmonic properties of non-equilibrium metal NPs.Item Metal nanoparticles for signal amplification in biosensors and signal suppression in fluorescence measurements(2021-05-05) Kogan, Molly; Webb, Lauren J.; Elber, Ron; Baiz, Carlos R; Gordon, VernitaMetal nanoparticles are particles made up of many individual metal atoms ranging in size from one nanometer to hundreds of nanometers in diameter. Originally these particles were used in glazes to make lustrous patterns on pottery. It was not until Michael Faraday’s discovery of colloidal gold in 1856 that nanoparticles were characterized. Since then, nanoparticles of different compositions, sizes, and shapes have been implemented in fields such as catalysis and biotechnology. This dissertation will address two applications of nanoparticles: silver nanoparticles (AgNPs) to amplify signal in a paper-based fluidic device and gold nanoparticles (AuNPs) to quench signal in studies of cell penetrating peptides (CPPs). First, the paper-based device used concentrates a “sandwich-type” immunoassay, made of a capture antibody bound to a magnetic microbead and a detection antibody bound to a AgNP label, at a screen-printed carbon electrode by a magnet. The AgNP labels are oxidized to Ag ions, reduced, and stripped off the electrode in a technique known as anodic stripping voltammetry. Originally, this device could only detect AgNP concentrations as low as 2.1 pM. Scanning electron microscopy (SEM) was used to investigate the percentage of AgNPs oxidized in this detection method enabling optimization of the electrochemical parameters for higher signal output. This lowered the detection limit to 2.6 fM, which is now at a sensitivity comparable to a commercial pregnancy test. Second, this dissertation focuses on the use of AuNPs to suppress signal in fluorescence studies of cell penetrating peptides (CPPs), a class of peptides so effective in crossing cellular membranes that they can be used to carry cargo such as proteins or small molecules into a cell. The mechanism by which CPPs can permeate cell membranes is poorly understood. Here we use a model system composed of phospholipid vesicles and small fluorescent peptides to investigate the transport and mechanism of these peptides interacting with the lipid bilayer. While fluorescence signal can reveal details such as the amount of peptide that transports inside the vesicles, it cannot determine the depth that a peptide penetrates through the vesicles. By growing AuNPs inside these vesicles, however, we can use fluorescence quenching to determine the proximity of the peptide to the center of the vesicles, which will be important as we continue to study CPPs and their permeation through cell membranes.Item Socially embedded and sustained point-of-use disinfection : enhancing silver nanoparticle enabled ceramic water filters with a Navajo pottery technique(2020-05-11) Rowles III, Lewis Stetson; Saleh, Navid B.; Lawler, Desmond F.; Kirisits, Mary Jo; Katz, Lynn E.; Kovar, DesiderioFor the nearly 800 million people that lack access to safe drinking water, point-of-use water treatment systems are a common solution to help provide potable water. Despite the availability of numerous treatment devices, failure at the implementation stage is common, mostly due to an oversight of the target community’s needs and thereby creating barriers for adoption. A classic example of communities with barriers against outside influence is the Navajo Nation, which also has extensive water contamination. Developing a water treatment solution for the Navajos thus has to consider community sentiment and empower the solution with local materials or century-old practices, which can possibly overcome such barriers and facilitate long-term adoption. This two-pronged dissertation centers around socially-aware water treatment. The first part is community-engaged research, aimed at identifying social drivers that underlie a community’s relationship with water and assessing the need for water treatment technologies. A qualitative study on water in indigenous communities in Mexico helped to identify the diverse drivers relating to water use. This aspect was further developed utilizing structural equation modeling to quantitatively link factors relating to water in the colonias in the United States. A systematic study on water quality in these unincorporated communities was also completed. The development of a socially-aware technology is the connecting link between the community-engaged research and the scientific laboratory research, which focuses the design of a socially appropriate nano-enabled ceramic device for disinfection. A natural polymer, Navajo pottery glaze of pinyon resin, was utilized to apply silver nanoparticles to ceramic water filters. The use of this material may help to facilitate adoption while rendering needed technological advancement to these widely used water treatment devices. Results show that embedding silver nanoparticles onto ceramic with this polymer allows for sustained dissolution of ionic silver in a range of waters and serves as a barrier to passivation from sulfide and chloride. The polymer was also found to control biofouling and to be toxic against Gram-positive bacteria. Overall, the community-engaged research provides valuable insight on understudied communities through innovative statistical methods, and the scientific research is one of the first to integrate traditional Native knowledge with novel materials engineering.Item The development of a metalloimmunoassay for the detection of NT-proBNP(2021-05-07) Pollok, Nicole Elise; Crooks, Richard M. (Richard McConnell); Richards, Ian; Schiavinato Eberlin, Livia; Anslyn, Eric V.; Hoffman, DavidThe purpose of this doctoral research is to develop a biosensor for the monitoring of heart failure (HF) in humans. Currently, there is no quantitative patient-facilitated method to monitor HF, and the physical symptoms that result are a poor representation of the acute state of the disease. The biomarker of interest is N-terminal prohormone brain natriuretic peptide (NT-proBNP) which is secreted from the cardiac muscle tissue when the heart is experiencing decompensation. The concentration of NT-proBNP has a direct correlation to the severity of HF, and it is used as the antigen in a metalloimmunoassay, where two monoclonal antibodies are used to sandwich NT-proBNP. One is conjugated to a magnetic microbead via a streptavidin-biotin interaction, and the other is conjugated to a 20 nm-diameter silver nanoparticle (AgNP) using a heterobifunctional cross-linker. The fully formed metalloimmunoassay is placed on a carbon screen-printed and Au electrodeposited sensing electrode to detect AgNP labels electrochemically. Ag charge collected from the assay is representative of the concentration of NT-proBNP in the sample. A phenomenon known as galvanic exchange (GE) is utilized in the detection of Ag. GE is a process that occurs when a zerovalent metal is immersed in a solution containing the oxidized form of a more noble metal. In this specific case, the exchange occurs between AgNP in the metalloimmunoassay and Au³⁺ generated on the sensing electrode. GE occurs because the standard reduction potential of Ag⁺ is slightly lower than Au³⁺. Significant findings of this project reveal that GE between AgNP and Au³⁺ is a process that results in only a partial exchange of AgNP with the Au³⁺ under physiologic conditions. It has also been found that, implementing two subsequent Au³⁺ electrogeneration steps improve the Ag collection efficiency and the reproducibility. Additionally, using heterobifunctional cross-linkers to covalently attach antibodies to AgNP and silver nanocubes (AgNCs) results in a lower limit of detection. These findings have led to the detection of NT-proBNP in buffer within clinically relevant ranges of 0.06-3.49 nM.Item The tolerance of a Rhodococcus drinking water isolate and Zoogloea ramigera to silver nanoparticles in biofilm and planktonic cultures(2011-08) Gao, Qiao Huan; Kirisits, Mary Jo; Katz, Lynn E.Spurred by a host of beneficial uses, the global use of nanoparticles is rapidly growing. Silver nanoparticles (Ag NPs) are used widely in consumer products, medicine, and the semiconductor industry. As nanoparticles become more commonly used, the transport of nanoparticles into the environment might negatively affect microorganisms in natural and engineered systems. The effects of Ag NPs on microorganisms have primarily been studied in planktonic or free-swimming cultures, but little work has been done to look at biofilm susceptibility to Ag NPs. This thesis describes bacterial tolerance, or the ability of an organism to survive exposure to an insult, to Ag NPs. The tolerance of planktonic and biofilm cells of the common wastewater treatment bacterium Zoogloea ramigera and a Rhodococcus strain isolated from drinking water was tested. These bacteria were exposed to different concentrations of Ag NPs, ranging from 0 to 25 mg/L, for a period of 5 hours. Results showed decreased tolerance with increasing Ag NP concentrations for both bacterial species. Z. ramigera biofilm cells are slightly more tolerant to Ag NPs than are planktonic cells. On the other hand, Rhodococcus planktonic and biofilm cells exhibit similar tolerance. However, in both cases, biofilm cells do not exhibit a striking protective effect against Ag NPs as compared to planktonic cells. This study shows that even short-term insults with Ag NPs can affect bacteria in engineered systems. A preliminary study of the shedding of free silver ions as a possible mechanism of Ag NP toxicity demonstrated that free silver ions were toxic to Escherichia coli in a 0.14M chloride environment. The data suggest that free silver ions can be pulled into solution from Ag NPs in chloride environments via ligand-promoted dissolution. Further work is needed to examine the antibacterial mechanism of Ag NPs against planktonic and biofilm cells to better understand how the release of nanoparticles into the environment can affect microorganisms in natural and engineered water systems.Item Transport and retention of silver nanoparticles in granular media filtration(2014-08) Kim, Ijung; Lawler, Desmond F.The increasing use of engineered nanoparticles such as silver nanoparticles (AgNPs) has focused more attention on the transport of nanoparticles in natural and engineered systems. Despite a substantial number of studies on the transport of nanoparticles in groundwater flow conditions, other conditions such as those in granular media filtration in water treatment plant have not been fully explored. This study was designed to investigate the transport of AgNPs in granular media filtration with a relatively high filtration velocity (~2 m/hr) and a low influent AgNP concentration (~100 [mu]g/L). Effects of several physical and chemical parameters on the transport and attachment of AgNPs were examined, focusing on the colloidal filtration theory and particle-particle interaction, respectively. Regarding the transport of AgNPs, four physical parameters (filter depth, filtration velocity, filter media size, and AgNP size) were varied at a fixed chemical condition. Positively charged branched polyethylenimine (BPEI) capped AgNPs were chosen to examine the transport of AgNPs under electrostatically favorable attachment conditions. The effects of filter depth, filtration velocity, and filter media size on transport of AgNPs were adequately described by the well-known colloidal filtration model. However, deviation from the model prediction was apparent as the AgNP size became smaller, implying a possible variation of nanoparticle properties in the smaller size such as 10 nm. In the AgNP attachment study, negatively charged citrate- and polyvinylpyrrolidone (PVP)-capped AgNPs were employed to examine the chemical effects on particle (AgNP)-particle (filter media) interaction. When the ionic strength and ion type in the background water were varied, the attachment of citrate AgNPs followed the DLVO theory. Ca- or Mg-citrate complexation was found to lead to charge neutralization, resulting in a greater AgNP deposition onto the filter media. However, PVP AgNPs were only marginally affected by the electrostatic effect, demonstrating a stronger stabilizing effect by PVP than citrate. When natural organic matter (NOM) was introduced in the background water, the deviation from the DLVO theory was considered primarily due to the steric interaction by NOM coating onto particles. Different amounts of AgNP deposition for different types of NOM suggest the variation of steric effects according to the molecular weight of NOM. The deposition of humic acid-coated AgNPs was similar regardless of the capping agent, indicating the possible displacement of the capping agent by NOM. The electrostatic and steric interactions affected the detachment of AgNPs as well as the attachment of AgNPs. The amount of detachment depended on the depth and width of the secondary energy minimum. Also, the detachment was enhanced with NOM coating, probably due to a weak attachment by the steric effect. However, the hydrodynamic force employed in this study was insufficient to yield a remarkable detachment. Overall, the retention profile was a relatively vertical line (i.e., equal deposition with depth) when the AgNP aggregation was prevented by the electrostatic or steric repulsion, implying homogeneous AgNP capture throughout the filter bed. On the other hand, ripening (the capture of particles by attraction to previously retained particles) was favored at the top of the filter bed when the AgNP aggregation was allowable.