Papers by Imali Mudunkotuwa
Aerosol Science and Technology, Oct 28, 2016
Langmuir, Jan 12, 2016
Understanding complex chemical changes that take place at nano-bio interfaces is of great concern... more Understanding complex chemical changes that take place at nano-bio interfaces is of great concern for being able to sustainably implement nanomaterials in key applications such as drug delivery, imaging, and environmental remediation. Typical in vitro assays use cell viability as a proxy to understanding nanotoxicity but often neglect how the nanomaterial surface can be altered by adsorption of solution-phase components in the medium. Protein coronas form on the nanomaterial surface when incubated in proteinaceous solutions. Herein, we apply a broad array of techniques to characterize and quantify protein corona formation on silica nanoparticle surfaces. The porosity and surface chemistry of the silica nanoparticles have been systematically varied. Using spectroscopic tools such as FTIR and circular dichroism, structural changes and kinetic processes involved in protein adsorption were evaluated. Additionally, by implementing thermogravimetric analysis, quantitative protein adsorption measurements allowed for the direct comparison between samples. Taken together, these measurements enabled the extraction of useful chemical information on protein binding onto nanoparticles in solution. Overall, we demonstrate that small alkylamines can increase protein adsorption and that even large polymeric molecules such as poly(ethylene glycol) (PEG) cannot prevent protein adsorption in these systems. The implications of these results as they relate to further understanding nano-bio interactions are discussed.
Fuel, Dec 1, 2015
Gas and particle emissions from co-firing coal and two types of biomass versus coal was evaluated... more Gas and particle emissions from co-firing coal and two types of biomass versus coal was evaluated in a circulating fluidized bed boiler operating with a constant energy input. Compared to coal, co-firing 50% oat hulls (by weight) significantly reduced the emission of particulate matter (PM) by 90%, polycyclic aromatic hydrocarbons (PAH) by 40%, metals by 65%, and fossil carbon dioxide by 40%. In contrast, co-firing 3.8% wood chips (by weight) had a negligible impact on the emissions of PM and PAH, but caused a 6% reduction in metals. Fuel-based emission factors for PM, metals, and organic species including biomass burning markers retene and levoglucosan, were determined. Enrichment factors (EF) were computed to examine the distribution of metals across PM, fly ash, and bottom ash and demonstrated enrichment in volatile metals (e.g. Fe, Al, and Cr) in PM and fly ash. Co-firing 50% oat hulls led to a significant depletion of K in PM and its enrichment in bottom ash. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis revealed a wide heterogeneity in particle sizes and compositions across particles for all fuel types. Overall, this study demonstrates that co-firing a 50% oat hulls with coal provides several benefits to air quality and outlines important changes to PM composition when biomass is co-fired with coal.
Environmental science. Nano, 2015
Evolution of nanoparticle surface composition in increasingly complex biological and environmenta... more Evolution of nanoparticle surface composition in increasingly complex biological and environmental matrices.
<div><p>ABSTRACT</p><p>Titanium dioxide (TiO<sub>2</sub>) par... more <div><p>ABSTRACT</p><p>Titanium dioxide (TiO<sub>2</sub>) particles, including nanoparticles with diameters smaller than 100 nm, are used extensively in consumer products. In a 2011 current intelligence bulletin, the National Institute of Occupational Safety and Health (NIOSH) recommended methods to assess worker exposures to fine and ultrafine TiO<sub>2</sub> particles and associated occupational exposure limits for these particles. However, there are several challenges and problems encountered with these recommended exposure assessment methods involving the accurate quantitation of titanium dioxide collected on air filters using acid digestion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, recommended digestion methods include the use of several hazardous chemicals, such as perchloric acid, which are typically unavailable in most accredited industrial hygiene laboratories. Other alternative methods that are used typically involve the use of nitric acid or combination of nitric acid and sulfuric acid, which yield very poor recoveries for titanium dioxide. Therefore, given the current state of the science, it is clear that a newer safe, reliable method is needed for exposure assessment. In this current study, a microwave-assisted acid digestion method has been specifically designed to improve the recovery of titanium in TiO<sub>2</sub> nanoparticles for analysis using ICP-OES. The optimum digestion conditions were determined by changing several variables including the acids used, digestion time and temperature. Consequently, the optimized digestion temperature of 210°C with concentrated sulfuric and nitric acid (2:1 v/v) resulted in a recovery of >90% for TiO<sub>2</sub>. The method is expected to provide for a more accurate quantification of airborne TiO<sub>2</sub> particles in the workplace environment.</p></div
Environmental Health Perspectives, 2017
Aerosol Science and Technology, 2016
Conventional methods to measure the metallic content of particles by size are time consuming and ... more Conventional methods to measure the metallic content of particles by size are time consuming and expensive, requiring collection of particles with a cascade impactor and subsequent metals analysis by inductively coupled plasma mass spectrometry (ICP-MS). In this work, we describe a rapid way to measure the size distribution of metal-containing particles from 10 nm to 20 μm, using a nano micro-orifice uniform-deposit impactor (nano-MOUDI) to size-selective and collect particles that are then analyzed with a field portable X-ray fluorescence (FP-XRF) to determine metal composition and concentration. The nano-MOUDI was used to sample a stainless-steel aerosol produced by a spark discharge system. The particle-laden substrates were then analyzed directly with FP-XRF and then with ICP-MS. Results from FP-XRF were linearly correlated with results from ICP-MS (R 2 = 0.91 for Fe and R 2 = 0.84 for Cr). Although the FP-XRF was unable to detect Fe particles at mass per substrate loadings less than 2.5 μg effectively, it produced results similar to those using the ICP-MS at a mass per substrate loading greater than 2.5 μg.
Journal of Occupational and Environmental Hygiene, 2016
Aerosol Science and Technology, 2016
Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to c... more Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to collect nanoparticles in the Nanoparticle Respiratory Deposition (NRD) sampler. Cylindrical (25mm diameter by 40-mm deep) foam with 110 pores per inch was housed in a 25-mm-diameter conductive polypropylene cassette cowl compatible with the NRD sampler. Pristine foam and nylon meshes were evaluated for metals content via elemental analysis. The size-selective collection efficiency of the foam was evaluated using salt (NaCl) and metal fume aerosols in independent tests. Collection efficiencies were compared to the nanoparticulate matter (NPM) criterion and a semi-empirical model for foam. Changes in collection efficiency and pressure drop of the foam and nylon meshes were measured after loading with metal fume particles as measures of substrate performance. Substantially less titanium was found in the foam (0.173 μg sampler -1 ) compared to the nylon mesh (125 μg sampler -1 ), improving the detection capabilities of the NRD sampler for titanium dioxide particles. The foam collection efficiency was similar to that of the nylon meshes and the NPM criterion (R 2 = 0.98, for NaCl), although the semi-empirical model underestimated the experimental efficiency (R 2 = 0.38). The pressure drop across the foam was 8% that of the nylon meshes when pristine and changed minimally with metal fume loading (~ 19 mg). In contrast, the pores of the nylon meshes clogged after loading with ~ 1 mg metal fume. These results indicate that foam is a suitable substrate to collect metal (except for cadmium) nanoparticles in the NRD sampler.
Environmental Science: Nano, 2016
The increasing use of copper oxide (CuO) nanoparticles (NPs) in medicine and industry demands an ... more The increasing use of copper oxide (CuO) nanoparticles (NPs) in medicine and industry demands an understanding of their potential toxicities.
Environmental Health Perspectives, 2013
Annals of Occupational Hygiene, 2015
Environmental Science: Nano, 2016
Bridging knowledge gaps in NanoEHS by identifying current fundamental science challenges and rese... more Bridging knowledge gaps in NanoEHS by identifying current fundamental science challenges and research needs.
Environmental Science: Nano, 2015
Evolution of nanoparticle surface composition in increasingly complex biological and environmenta... more Evolution of nanoparticle surface composition in increasingly complex biological and environmental matrices.
Journal of Occupational and Environmental Hygiene, 2016
Titanium dioxide (TiO 2 ) particles, including nanoparticles with diameters smaller than 100 nm, ... more Titanium dioxide (TiO 2 ) particles, including nanoparticles with diameters smaller than 100 nm, are used extensively in consumer products. In a 2011 current intelligence bulletin, the National Institute of Occupational Safety and Health (NIOSH) recommended methods to assess worker exposures to fine and ultrafine TiO 2 particles and associated occupational exposure limits for these particles. However, there are several challenges and problems encountered with these recommended exposure assessment methods involving the accurate quantitation of titanium dioxide collected on air filters using acid digestion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, recommended digestion methods include the use of chemicals, such as perchloric acid, which are typically unavailable in most accredited industrial hygiene laboratories due to highly corrosive and oxidizing properties. Other alternative methods that are used typically involve the use of nitric acid or combination of nitric acid and sulfuric acid, which yield very poor recoveries for titanium dioxide. Therefore, given the current state of the science, it is clear that a new method is needed for exposure assessment. In this current study, a microwave-assisted acid digestion method has been specifically designed to improve the recovery of titanium in TiO 2 nanoparticles for quantitative analysis using ICP-OES. The optimum digestion conditions were determined by changing several variables including the acids used, digestion time, and temperature. Consequently, the optimized digestion temperature of 210°C with concentrated sulfuric and nitric acid (2:1 v/v) resulted in a recovery of >90% for TiO 2 . The method is expected to provide for a more accurate quantification of airborne TiO 2 particles in the workplace environment.
Langmuir, 2014
Nanoparticles in biological media form dynamic entities as a result of competitive adsorption of ... more Nanoparticles in biological media form dynamic entities as a result of competitive adsorption of proteins on nanoparticle surfaces called protein coronas. The protein affinity toward nanoparticle surfaces potentially depends on the constituent amino acid side chains which are on the protein exterior and thus exposed to the solution and available for interaction. Therefore, studying the adsorption of individual amino acids on nanoparticle surfaces can provide valuable insights into the overall evolution of nanoparticles in solution and the protein corona that forms. In the current study, the surface adsorption of L-histidine on TiO 2 nanoparticles with a diameter of 5 nm at pH 7.4 (physiological pH) is studied from both macroscopic and molecular perspectives. Quantitative adsorption measurements of L-histidine on 5 nm TiO 2 particles yield maximum adsorption coverage of 6.2 ± 0.3 × 10 13 molecules cm -2 at 293 K and pH 7.4. These quantitative adsorption measurements also yield values for the equilibrium constant and free energy of adsorption of K = 4.3 ± 0.5 × 10 2 L mol -1 and ΔG = -14.8 ± 0.3 kJ mol -1 , respectively. Detailed analysis of the adsorption between histidine and 5 nm TiO 2 nanoparticle surfaces with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy indicates both the imidazole side chain and the amine group interacting with the nanoparticle surface and the adsorption to be reversible. The adsorption results in no change in surface charge and therefore does not change nanoparticle-nanoparticle interactions and thus aggregation behavior of these 5 nm TiO 2 nanoparticles in aqueous solution.
Aerosol Science and Technology, 2015
Environmental Science: Nano, 2014
Given the increased use of iron-containing nanoparticles in a number of applications, it is impor... more Given the increased use of iron-containing nanoparticles in a number of applications, it is important to understand any effects that iron-containing nanoparticles can have on the environment and human health. Since iron concentrations are extremely low in body fluids, there is potential that iron-containing nanoparticles may influence the ability of bacteria to scavenge iron for growth, affect virulence and inhibit antimicrobial peptide (AMP) function. In this study, Pseudomonas aeruginosa (PA01) and AMPs were exposed to iron oxide nanoparticles, hematite (α-Fe 2 O 3 ), of different sizes ranging from 2 to 540 nm (2 ± 1, 43 ± 6, 85 ± 25 and 540 ± 90 nm) in diameter. Here we show that the greatest effect on bacterial growth, biofilm formation, and AMP function impairment is found when exposed to the smallest particles. These results are attributed in large part to enhanced dissolution observed for the smallest particles and an increase in the amount of bioavailable iron. Furthermore, AMP function can be additionally impaired by adsorption onto nanoparticle surfaces. In particular, lysozyme readily adsorbs onto the nanoparticle surface which can lead to loss of peptide activity. Thus, this current study shows that co-exposure of nanoparticles and known pathogens can impact host innate immunity. Therefore, it is important that future studies be designed to further understand these types of impacts. † Electronic supplementary information (ESI) available: ESI contains a detailed description of particle synthesis and sources and a schematic diagram of the antimicrobial peptide assay. See
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Papers by Imali Mudunkotuwa