Browsing by Author "Kang, Seju"

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    Highly porous gold supraparticles as surface-enhanced Raman spectroscopy (SERS) substrates for sensitive detection of environmental contaminants
    Kang, Seju; Wang, Wei; Rahman, Asifur; Nam, Wonil; Zhou, Wei; Vikesland, Peter J. (Royal Society of Chemistry, 2022-11-15)
    Surface-enhanced Raman spectroscopy (SERS) has great potential as an analytical technique for environmental analyses. In this study, we fabricated highly porous gold (Au) supraparticles (i.e., ∼100 μm diameter agglomerates of primary nano-sized particles) and evaluated their applicability as SERS substrates for the sensitive detection of environmental contaminants. Facile supraparticle fabrication was achieved by evaporating a droplet containing an Au and polystyrene (PS) nanoparticle mixture on a superamphiphobic nanofilament substrate. Porous Au supraparticles were obtained through the removal of the PS phase by calcination at 500 °C. The porosity of the Au supraparticles was readily adjusted by varying the volumetric ratios of Au and PS nanoparticles. Six environmental contaminants (malachite green isothiocyanate, rhodamine B, benzenethiol, atrazine, adenine, and gene segment) were successfully adsorbed to the porous Au supraparticles, and their distinct SERS spectra were obtained. The observed linear dependence of the characteristic Raman peak intensity for each environmental contaminant on its aqueous concentration reveals the quantitative SERS detection capability by porous Au supraparticles. The limit of detection (LOD) for the six environmental contaminants ranged from ∼10 nM to ∼10 μM, which depends on analyte affinity to the porous Au supraparticles and analyte intrinsic Raman cross-sections. The porous Au supraparticles enabled multiplex SERS detection and maintained comparable SERS detection sensitivity in wastewater influent. Overall, we envision that the Au supraparticles can potentially serve as practical and sensitive SERS devices for environmental analysis applications.
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    Life Cycle Impact Assessment of Iron Oxide (Fe3O4/γ-Fe2O3) Nanoparticle Synthesis Routes
    Rahman, Asifur; Kang, Seju; McGinnis, Sean; Vikesland, Peter J. (2022)
    The synthesis of superparamagnetic iron oxide nanoparticles (FeOx-NPs) has rapidly developed over the past decade due to their wide-ranging applications in research and technology. However, at present there exists very limited knowledge about the environmental impacts of the various input materials and the energy required for different FeOx-NP synthesis approaches. In this study, we used cradle-to-gate life cycle assessment (LCA) to analyze and compare the environmental impacts of FeOx-NPs produced via seven common synthesis routes. Four different functional units (i.e., mass, mean particle size, specific surface area, and saturation magnetization) were used to normalize the environmental impacts and evaluate the corresponding changes. Overall, physical and biological synthesis routes exhibited high environmental impacts due to their higher input material and energy requirements. Interestingly, biological syntheses had the highest environmental impacts due to their reliance on bacterial culture media. All of the chemical synthesis routes had lower environmental impacts except the thermal decomposition method, which had higher environmental impacts due its use of non-polar organic solvents during synthesis. The lab-scale LCA inventory data and analysis presented here addresses the existing data gaps and helps guide future research for FeOx-NP synthesis under industrial conditions. The information generated by this effort aids in the identification of environmentally friendly and sustainable production pathways for FeOx-NPs.
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    Nanobiotechnology Enabled Environmental Sensing of Water and Wastewater
    Kang, Seju (Virginia Tech, 2023-01-13)
    Many environmental compartments are acknowledged transmission routes for infectious diseases, antibiotic resistance, and anthropogenic pollution. The need for environmental sensing has consistently been stressed as a means to minimize public health threats caused by such contaminants. Many analytical detection techniques have been developed and applied for environmental sensing. However, these techniques are often reliant upon centralized facilities and require intensive resources. For these reasons their use can be challenging under resource-constrained conditions characterized by poor water, sanitation, and hygiene (WASH) services. In this dissertation, we developed biotechnology- and/or nanotechnology-advanced analytical tools for environmental sensing that have potential for future application in regions with poor WASH services. First, loop-mediated isothermal amplification (LAMP) and nanopore sequencing were applied to develop assays for the detection of SARS-CoV-2, the causative agent of COVID-19, in wastewater samples. Second, surface-enhanced Raman spectroscopy (SERS) was applied for environmental detection of a range of analytes. Gold nanoparticle (AuNP)-based SERS substrates were fabricated by droplet evaporation-induced aggregation on a hydrophobic substrate. These SERS substrates were then applied for the detection of antibiotic resistance genes (ARGs) and other environmental contaminants (e.g., dye or hydrophobic organic contaminants). In a separate study, Au nanostructured SERS substrates were fabricated and applied for pH sensing in a range of environmental media. Finally, the environmental impact of an AuNP-based colorimetric detection assay was assessed via life cycle assessment.