University of Minnesota Ph.D. dissertation. May 2019. Major: Chemistry. Advisor: Christy Haynes. ... more University of Minnesota Ph.D. dissertation. May 2019. Major: Chemistry. Advisor: Christy Haynes. 1 computer file (PDF); xvi, 148 pages.
Nicole Moody, Samuel Sesena, Dane W. deQuilettes, Benjia Dak Dou, Richard Swartwout, Anna Johnson... more Nicole Moody, Samuel Sesena, Dane W. deQuilettes, Benjia Dak Dou, Richard Swartwout, Anna Johnson, Udochukwu Eze, Roberto Brenes, Matthew Johnston, Vladimir Bulovic, and Moungi G. Bawendi are members of Tata-MIT GridEdge Solar, an interdisciplinary research program at the Massachusetts Institute of Technology working toward scalable design and manufacturing of lightweight, flexible solar cells. Joseph T. Buchman and Christy L. Haynes are part of the Center for Sustainable Nanotechnology, a multi-institutional partnership aimed at understanding the fundamental chemical and physical processes that govern the transformations and interactions of nanoparticles in the environment.
We highlight three articles in which investigators assessed the impacts of nanoparticle shape on ... more We highlight three articles in which investigators assessed the impacts of nanoparticle shape on their interactions with organisms.
Lithium intercalation compounds, such as the complex metal oxide, lithium nickel manganese cobalt... more Lithium intercalation compounds, such as the complex metal oxide, lithium nickel manganese cobalt oxide (LiNixMnyCo1-x-yO2, herein referred to as NMC), have demonstrated their utility as energy storage materials. In response...
The Supporting Information file contains 5 pages and 6 figures. S1 S1. Size Distribution of Synth... more The Supporting Information file contains 5 pages and 6 figures. S1 S1. Size Distribution of Synthesized MSNs Three batches of MSNs were synthesized in this work for plant exposures and coating with chitosan. After their synthesis, the MSNs were characterized using transmission electron microscopy so that their diameter could be determined with ImageJ. 1 Histograms of the size distributions of these three batches are shown in Figure S1.
The paper extends an impulsive control-theoretical framework towards dynamic systems in the space... more The paper extends an impulsive control-theoretical framework towards dynamic systems in the space of measures. We consider a transport equation describing the time-evolution of a conservative "mass" (probability measure), which represents an infinite ensemble of interacting particles. The driving vector field contains nonlocal terms and it is affine in the control variable. The control is assumed to be common for all the agents, i.e., it is a function of time variable only. The main feature of the addressed model is the admittance of "shock" impacts, i.e. controls, whose influence on each agent can be arbitrary close to Dirac-type distributions. We construct an impulsive relaxation of this system and of the corresponding optimal control problem. For the latter we establish a necessary optimality condition in the form of Pontryagin's Maximum Principle.
There has been a surge of consumer products that incorporate nanoparticles, which are used to imp... more There has been a surge of consumer products that incorporate nanoparticles, which are used to improve or impart new functionalities to the products based on their unique physicochemical properties. With such an increase in products containing nanomaterials, there is a need to understand their potential impacts on the environment. This is often done using various biological models that are abundant in the different environmental compartments where the nanomaterials may end up after use. Beyond studying whether nanomaterials simply kill an organism, the molecular mechanisms by which nanoparticles exhibit toxicity have been extensively studied. Some of the main mechanisms include (1) direct nanoparticle association with an organism's cell surface, where the membrane can be damaged or initiate internal signaling pathways that damage the cell, (2) dissolution of the material, releasing toxic ions that impact the organism, generally through impairing important enzyme functions or through direct interaction with a cell's DNA, and (3) the generation of reactive oxygen species and subsequent oxidative stress on an organism, which can also damage important enzymes or an organism's genetic material. This Account reviews these toxicity mechanisms, presenting examples for each with different types of nanomaterials. Understanding the mechanism of nanoparticle toxicity will inform efforts to redesign nanoparticles with reduced environmental impact. The redesign strategies will need to be chosen based on the major mode of toxicity, but also considering what changes can be made to the nanomaterial without impacting its ability to perform in its intended application. To reduce interactions with the cell surface, nanomaterials can be designed to have a negative surface charge, use ligands such as polyethylene glycol that reduce protein binding, or have a morphology that discourages binding with a cell surface. To reduce the nanoparticle dissolution to toxic ions, the toxic species can be replaced with less toxic elements that have similar properties, the nanoparticle can be capped with a shell material, the morphology of the nanoparticle can be chosen to minimize surface area and thus minimize dissolution, or a chelating agent can be co-introduced or functionalized onto the nanomaterial's surface. To reduce the production of reactive oxygen species, the band gap of the material can be tuned either by using different elements or by doping, a shell layer can be added to inhibit direct contact with the core, or antioxidant molecules can be tethered to the nanoparticle surface. When redesigning nanoparticles, it will be important to test that the redesign strategy actually reduces toxicity to organisms from relevant environmental compartments. It is also necessary to confirm that the nanomaterial still demonstrates the critical physicochemical properties that inspired its inclusion in a product or device.
Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic r... more Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well.
Langmuir : the ACS journal of surfaces and colloids, Jan 5, 2018
The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environmen... more The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environment external to cells. Interaction with nanomaterials can alter the integrity of the cytoplasmic membrane through the formation of holes and membrane thinning, which can ultimately lead to adverse biological impacts. Here we use supported lipid bilayers as experimental models for the cytoplasmic membrane to investigate the impact of quantum dots functionalized with the cationic polymer poly(diallyldimethylammonium chloride) (PDDA) on membrane structure. Using quartz crystal microbalance with dissipation monitoring we show that the positively charged quantum dots attach to and induce structural rearrangement to zwitterionic bilayers in solely the liquid-disordered phase and in those containing phase-segregated liquid-ordered domains. Real-time atomic force microscopy imaging revealed that PDDA-coated quantum dots, and to a lesser extent PDDA itself, induced disappearance of liquid-ordered d...
Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable ... more Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable and are being proposed for use as a material for medical imaging or drug delivery to composites. With their potential for widespread use they may potentially be released into the aquatic environment as are many chemicals used for these purposes. It is generally thought that nanodiamonds are innocuous, but toxicity may occur due to surface functionalization. This study investigated the potential oxidative stress and antioxidant response of enterocytes in a freshwater invertebrate, Daphnia magna, a common aquatic invertebrate for ecotoxicological studies, in response to two types of functionalized nanodiamonds (polyallylamine and oxidized). We also examined how the size of the nanomaterial may influence toxicity by testing two different sizes (5 nm and 15 nm) of nanodiamonds with the same functionalization. Adults of Daphnia magna were exposed to three concentrations of each of the nanodia...
We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria.... more We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria. We assessed the toxicity of 4 nm polyallylamine hydrochloride-wrapped gold nanoparticles to a panel of bacteria from diverse environmental niches. The bacteria experienced a range of toxicities as evidenced by the different minimum bactericidal concentrations determined; the sensitivities of the bacteria was = > MR-4 > > MR-1. Interactions between gold nanoparticles and molecular components of the cell wall were investigated by TEM, flow cytometry, and computational modeling. Binding results showed a general trend that bacteria with smooth LPS bind more PAH AuNPs than bacteria with rough LPS. Computational models reveal that PAH migrates to phosphate groups in the core of the LPS structure. Overall, our results demonstrate that simple interactions between nanoparticles and the bacterial cell wall cannot fully account for observed trends in toxicity, which points to the importan...
While there is great interest in understanding the fate and transport of nanomaterials in the env... more While there is great interest in understanding the fate and transport of nanomaterials in the environment and in biological systems, the detection of nanomaterials in complex matrices by fluorescence methods is complicated by photodegradation, blinking, and the presence of natural organic material and other fluorescent background signals that hamper detection of fluorescent nanomaterials of interest. Optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond nanoparticles provides a pathway toward background-free fluorescence measurements, as the application of a resonant microwave field can selectively modulate the intensity from NV centers in nanodiamonds of various diameters in complex materials systems using on-resonance and off-resonance microwave fields. This work represents the first investigation showing how nanoparticle diameter impacts the NV center lifetime and thereby directly impacts the accessible contrast and signal-to-noise ratio when us...
This highlight outlines recent methodologies that integrate engineered nanomaterial research and ... more This highlight outlines recent methodologies that integrate engineered nanomaterial research and development with life-cycle assessment.
This work investigates the biological impact of LixNiyMnzCo1−y−zO2, a class of cathode materials ... more This work investigates the biological impact of LixNiyMnzCo1−y−zO2, a class of cathode materials used in lithium ion batteries.
Polyelectrolyte (PE) wrapping of colloidal nanoparticles (NPs) is a standard method to control NP... more Polyelectrolyte (PE) wrapping of colloidal nanoparticles (NPs) is a standard method to control NP surface chemistry and charge. Because excess polyelectrolytes are usually employed in the surface modification process, it is critical to evaluate different purification strategies to obtain a clean final product and thus avoid ambiguities in the source of effects on biological systems. In this work, 4 nm diameter gold nanoparticles (AuNPs) were wrapped with 15 kDa poly(allylamine hydrochloride) (PAH), and three purification strategies were applied: (a) diafiltration or either (b) one round or (c) two rounds of centrifugation. The bacterial toxicity of each of these three PAH-AuNP samples was evaluated for the bacterium Shewanella oneidensis MR-1 and is quantitatively correlated with the amount of unbound PAH molecules in the AuNP suspensions, as judged by X-ray photoelectron spectroscopy, nuclear magnetic resonance experiments and quantification using fluorescent assay. Dialysis experi...
Mesoporous silica nanoparticles are promising drug delivery agents; however, their interaction wi... more Mesoporous silica nanoparticles are promising drug delivery agents; however, their interaction with various in vivo biological components is still under investigation. In this work, the impact of sub-50 nm diameter mesoporous silica nanoparticles on platelet function is investigated using a microfluidic platform to model blood vessel characteristics. Platelet adhesion and aggregation in the presence of mesoporous silica nanoparticles is investigated, controlling whether or not platelets are activated ahead of nanoparticle exposure. The results indicate that nanoparticles slightly compromise platelet adhesion to endothelial cells at low nanoparticle doses, but that high nanoparticle doses significantly increase the number of platelet adhesion events, leading to higher probability for uncontrolled platelet actions (e.g. clot formation in vivo). High nanoparticle doses also induced platelet aggregation. While platelet activation and aggregation occurred, in no case did nanoparticle exposure result in significant loss of platelet viability; as such, this work clearly demonstrates that aspects besides viability, such as cellular adhesion and interaction with other cell types, have to be considered in the context of nanotoxicology. This simple and highly adaptable analytical platform will be useful for further nanotoxicity studies involving other nanoparticle and cell types.
ABSTRACT The potential of replacing petroleum fuels with renewable biofuels has drawn significant... more ABSTRACT The potential of replacing petroleum fuels with renewable biofuels has drawn significant public interest. Many states have imposed biodiesel mandates or incentives to use commercial biodiesel blends. We present an inquiry-driven experiment where students are given the tasks to gather samples, develop analytical methods using various instrumental methods, such as HPLC, 1H-NMR, and ATR-FTIR, make measurements, and analyze the results to determine the volume percent of biodiesel in commercial diesel blends. The project develops students? appreciation of the usefulness of chemistry by working with ?real? samples from their daily lives, and skills to critically compare and contrast the strengths and weaknesses of various instrumental techniques for quantitative analysis.
Science blogging is a common practice for communication with broad audiences; however, the effect... more Science blogging is a common practice for communication with broad audiences; however, the effectiveness of blogs for promoting public engagement with scientific material has not been fully assessed. This study investigated reader engagement after reading either a scientific blog post or a related expository-style article by comparing whether participants volunteered for further email communications at the end of the study. We found that the blog group showed significantly greater engagement than the expository reading group. Results provide evidence for the effectiveness of blogging as a science outreach tool, and suggest potential future research topics related to age, gender, and geography.
Next generation displays and lighting applications are increasingly using inorganic quantum dots ... more Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs (e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD–polymer nano-composites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in polyIJmethyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD–PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decrease in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nano-composite but also to determine the form of the released nanoparticles (e.g. ions or polymer fragments).
University of Minnesota Ph.D. dissertation. May 2019. Major: Chemistry. Advisor: Christy Haynes. ... more University of Minnesota Ph.D. dissertation. May 2019. Major: Chemistry. Advisor: Christy Haynes. 1 computer file (PDF); xvi, 148 pages.
Nicole Moody, Samuel Sesena, Dane W. deQuilettes, Benjia Dak Dou, Richard Swartwout, Anna Johnson... more Nicole Moody, Samuel Sesena, Dane W. deQuilettes, Benjia Dak Dou, Richard Swartwout, Anna Johnson, Udochukwu Eze, Roberto Brenes, Matthew Johnston, Vladimir Bulovic, and Moungi G. Bawendi are members of Tata-MIT GridEdge Solar, an interdisciplinary research program at the Massachusetts Institute of Technology working toward scalable design and manufacturing of lightweight, flexible solar cells. Joseph T. Buchman and Christy L. Haynes are part of the Center for Sustainable Nanotechnology, a multi-institutional partnership aimed at understanding the fundamental chemical and physical processes that govern the transformations and interactions of nanoparticles in the environment.
We highlight three articles in which investigators assessed the impacts of nanoparticle shape on ... more We highlight three articles in which investigators assessed the impacts of nanoparticle shape on their interactions with organisms.
Lithium intercalation compounds, such as the complex metal oxide, lithium nickel manganese cobalt... more Lithium intercalation compounds, such as the complex metal oxide, lithium nickel manganese cobalt oxide (LiNixMnyCo1-x-yO2, herein referred to as NMC), have demonstrated their utility as energy storage materials. In response...
The Supporting Information file contains 5 pages and 6 figures. S1 S1. Size Distribution of Synth... more The Supporting Information file contains 5 pages and 6 figures. S1 S1. Size Distribution of Synthesized MSNs Three batches of MSNs were synthesized in this work for plant exposures and coating with chitosan. After their synthesis, the MSNs were characterized using transmission electron microscopy so that their diameter could be determined with ImageJ. 1 Histograms of the size distributions of these three batches are shown in Figure S1.
The paper extends an impulsive control-theoretical framework towards dynamic systems in the space... more The paper extends an impulsive control-theoretical framework towards dynamic systems in the space of measures. We consider a transport equation describing the time-evolution of a conservative "mass" (probability measure), which represents an infinite ensemble of interacting particles. The driving vector field contains nonlocal terms and it is affine in the control variable. The control is assumed to be common for all the agents, i.e., it is a function of time variable only. The main feature of the addressed model is the admittance of "shock" impacts, i.e. controls, whose influence on each agent can be arbitrary close to Dirac-type distributions. We construct an impulsive relaxation of this system and of the corresponding optimal control problem. For the latter we establish a necessary optimality condition in the form of Pontryagin's Maximum Principle.
There has been a surge of consumer products that incorporate nanoparticles, which are used to imp... more There has been a surge of consumer products that incorporate nanoparticles, which are used to improve or impart new functionalities to the products based on their unique physicochemical properties. With such an increase in products containing nanomaterials, there is a need to understand their potential impacts on the environment. This is often done using various biological models that are abundant in the different environmental compartments where the nanomaterials may end up after use. Beyond studying whether nanomaterials simply kill an organism, the molecular mechanisms by which nanoparticles exhibit toxicity have been extensively studied. Some of the main mechanisms include (1) direct nanoparticle association with an organism's cell surface, where the membrane can be damaged or initiate internal signaling pathways that damage the cell, (2) dissolution of the material, releasing toxic ions that impact the organism, generally through impairing important enzyme functions or through direct interaction with a cell's DNA, and (3) the generation of reactive oxygen species and subsequent oxidative stress on an organism, which can also damage important enzymes or an organism's genetic material. This Account reviews these toxicity mechanisms, presenting examples for each with different types of nanomaterials. Understanding the mechanism of nanoparticle toxicity will inform efforts to redesign nanoparticles with reduced environmental impact. The redesign strategies will need to be chosen based on the major mode of toxicity, but also considering what changes can be made to the nanomaterial without impacting its ability to perform in its intended application. To reduce interactions with the cell surface, nanomaterials can be designed to have a negative surface charge, use ligands such as polyethylene glycol that reduce protein binding, or have a morphology that discourages binding with a cell surface. To reduce the nanoparticle dissolution to toxic ions, the toxic species can be replaced with less toxic elements that have similar properties, the nanoparticle can be capped with a shell material, the morphology of the nanoparticle can be chosen to minimize surface area and thus minimize dissolution, or a chelating agent can be co-introduced or functionalized onto the nanomaterial's surface. To reduce the production of reactive oxygen species, the band gap of the material can be tuned either by using different elements or by doping, a shell layer can be added to inhibit direct contact with the core, or antioxidant molecules can be tethered to the nanoparticle surface. When redesigning nanoparticles, it will be important to test that the redesign strategy actually reduces toxicity to organisms from relevant environmental compartments. It is also necessary to confirm that the nanomaterial still demonstrates the critical physicochemical properties that inspired its inclusion in a product or device.
Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic r... more Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well.
Langmuir : the ACS journal of surfaces and colloids, Jan 5, 2018
The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environmen... more The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environment external to cells. Interaction with nanomaterials can alter the integrity of the cytoplasmic membrane through the formation of holes and membrane thinning, which can ultimately lead to adverse biological impacts. Here we use supported lipid bilayers as experimental models for the cytoplasmic membrane to investigate the impact of quantum dots functionalized with the cationic polymer poly(diallyldimethylammonium chloride) (PDDA) on membrane structure. Using quartz crystal microbalance with dissipation monitoring we show that the positively charged quantum dots attach to and induce structural rearrangement to zwitterionic bilayers in solely the liquid-disordered phase and in those containing phase-segregated liquid-ordered domains. Real-time atomic force microscopy imaging revealed that PDDA-coated quantum dots, and to a lesser extent PDDA itself, induced disappearance of liquid-ordered d...
Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable ... more Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable and are being proposed for use as a material for medical imaging or drug delivery to composites. With their potential for widespread use they may potentially be released into the aquatic environment as are many chemicals used for these purposes. It is generally thought that nanodiamonds are innocuous, but toxicity may occur due to surface functionalization. This study investigated the potential oxidative stress and antioxidant response of enterocytes in a freshwater invertebrate, Daphnia magna, a common aquatic invertebrate for ecotoxicological studies, in response to two types of functionalized nanodiamonds (polyallylamine and oxidized). We also examined how the size of the nanomaterial may influence toxicity by testing two different sizes (5 nm and 15 nm) of nanodiamonds with the same functionalization. Adults of Daphnia magna were exposed to three concentrations of each of the nanodia...
We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria.... more We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria. We assessed the toxicity of 4 nm polyallylamine hydrochloride-wrapped gold nanoparticles to a panel of bacteria from diverse environmental niches. The bacteria experienced a range of toxicities as evidenced by the different minimum bactericidal concentrations determined; the sensitivities of the bacteria was = > MR-4 > > MR-1. Interactions between gold nanoparticles and molecular components of the cell wall were investigated by TEM, flow cytometry, and computational modeling. Binding results showed a general trend that bacteria with smooth LPS bind more PAH AuNPs than bacteria with rough LPS. Computational models reveal that PAH migrates to phosphate groups in the core of the LPS structure. Overall, our results demonstrate that simple interactions between nanoparticles and the bacterial cell wall cannot fully account for observed trends in toxicity, which points to the importan...
While there is great interest in understanding the fate and transport of nanomaterials in the env... more While there is great interest in understanding the fate and transport of nanomaterials in the environment and in biological systems, the detection of nanomaterials in complex matrices by fluorescence methods is complicated by photodegradation, blinking, and the presence of natural organic material and other fluorescent background signals that hamper detection of fluorescent nanomaterials of interest. Optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond nanoparticles provides a pathway toward background-free fluorescence measurements, as the application of a resonant microwave field can selectively modulate the intensity from NV centers in nanodiamonds of various diameters in complex materials systems using on-resonance and off-resonance microwave fields. This work represents the first investigation showing how nanoparticle diameter impacts the NV center lifetime and thereby directly impacts the accessible contrast and signal-to-noise ratio when us...
This highlight outlines recent methodologies that integrate engineered nanomaterial research and ... more This highlight outlines recent methodologies that integrate engineered nanomaterial research and development with life-cycle assessment.
This work investigates the biological impact of LixNiyMnzCo1−y−zO2, a class of cathode materials ... more This work investigates the biological impact of LixNiyMnzCo1−y−zO2, a class of cathode materials used in lithium ion batteries.
Polyelectrolyte (PE) wrapping of colloidal nanoparticles (NPs) is a standard method to control NP... more Polyelectrolyte (PE) wrapping of colloidal nanoparticles (NPs) is a standard method to control NP surface chemistry and charge. Because excess polyelectrolytes are usually employed in the surface modification process, it is critical to evaluate different purification strategies to obtain a clean final product and thus avoid ambiguities in the source of effects on biological systems. In this work, 4 nm diameter gold nanoparticles (AuNPs) were wrapped with 15 kDa poly(allylamine hydrochloride) (PAH), and three purification strategies were applied: (a) diafiltration or either (b) one round or (c) two rounds of centrifugation. The bacterial toxicity of each of these three PAH-AuNP samples was evaluated for the bacterium Shewanella oneidensis MR-1 and is quantitatively correlated with the amount of unbound PAH molecules in the AuNP suspensions, as judged by X-ray photoelectron spectroscopy, nuclear magnetic resonance experiments and quantification using fluorescent assay. Dialysis experi...
Mesoporous silica nanoparticles are promising drug delivery agents; however, their interaction wi... more Mesoporous silica nanoparticles are promising drug delivery agents; however, their interaction with various in vivo biological components is still under investigation. In this work, the impact of sub-50 nm diameter mesoporous silica nanoparticles on platelet function is investigated using a microfluidic platform to model blood vessel characteristics. Platelet adhesion and aggregation in the presence of mesoporous silica nanoparticles is investigated, controlling whether or not platelets are activated ahead of nanoparticle exposure. The results indicate that nanoparticles slightly compromise platelet adhesion to endothelial cells at low nanoparticle doses, but that high nanoparticle doses significantly increase the number of platelet adhesion events, leading to higher probability for uncontrolled platelet actions (e.g. clot formation in vivo). High nanoparticle doses also induced platelet aggregation. While platelet activation and aggregation occurred, in no case did nanoparticle exposure result in significant loss of platelet viability; as such, this work clearly demonstrates that aspects besides viability, such as cellular adhesion and interaction with other cell types, have to be considered in the context of nanotoxicology. This simple and highly adaptable analytical platform will be useful for further nanotoxicity studies involving other nanoparticle and cell types.
ABSTRACT The potential of replacing petroleum fuels with renewable biofuels has drawn significant... more ABSTRACT The potential of replacing petroleum fuels with renewable biofuels has drawn significant public interest. Many states have imposed biodiesel mandates or incentives to use commercial biodiesel blends. We present an inquiry-driven experiment where students are given the tasks to gather samples, develop analytical methods using various instrumental methods, such as HPLC, 1H-NMR, and ATR-FTIR, make measurements, and analyze the results to determine the volume percent of biodiesel in commercial diesel blends. The project develops students? appreciation of the usefulness of chemistry by working with ?real? samples from their daily lives, and skills to critically compare and contrast the strengths and weaknesses of various instrumental techniques for quantitative analysis.
Science blogging is a common practice for communication with broad audiences; however, the effect... more Science blogging is a common practice for communication with broad audiences; however, the effectiveness of blogs for promoting public engagement with scientific material has not been fully assessed. This study investigated reader engagement after reading either a scientific blog post or a related expository-style article by comparing whether participants volunteered for further email communications at the end of the study. We found that the blog group showed significantly greater engagement than the expository reading group. Results provide evidence for the effectiveness of blogging as a science outreach tool, and suggest potential future research topics related to age, gender, and geography.
Next generation displays and lighting applications are increasingly using inorganic quantum dots ... more Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs (e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD–polymer nano-composites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in polyIJmethyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD–PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decrease in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nano-composite but also to determine the form of the released nanoparticles (e.g. ions or polymer fragments).
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