Browsing by Subject "Silver nanoparticle"
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Item Effects of macromolecular capping on the fate and transport of engineered silver nanoparticles in granular media filtration(2017-05) Zhu, Tongren; Lawler, Desmond F.; Bonnecaze, Roger T.; Katz, Lynn E.; Lau, Boris L.T.; Saleh, Navid B.The increasing use of silver nanoparticles (AgNPs) inevitably leads to their release into the environment and raises the importance of removing these emerging “pollutants” by the conventional drinking water treatment processes. Granular media filtration is one of the primary treatment processes to remove aqueous colloids and its performance is related to surface properties of AgNPs and aqueous chemistry. This research focused on the fate and transport of engineered AgNPs in granular media filtration after humic acid (HA) exposure and sulfidation. The Derjaguin-Landau-Verwey-Overbeek (DLVO) energy of interaction was updated to account for the effects of the surface capping layer. The DLVO energy of interaction was first updated to include the effect of “soft” surface capping layer. Ohshima’s soft particle theory was numerically applied to obtain the electric double layer (EDL) interaction. Pair-wise summation between two multi-layered half-spaces was employed to compute the van der Waals (vdW) attraction. The updated calculation revealed that, in addition to steric hindrance, stability of polymer-capped particles can also be enhanced by an increased EDL repulsion from mixing and compression of the charged polymer capping, and a reduced vdW attraction due to the attenuation by the polymer capping which has a lower Hamaker constant than the core material. The effects of sulfidation of polyvinylpyrrolidone (PVP) capped AgNPs under different conditions of HA exposure were studied. ζ-potential of AgNPs became more negative upon sulfidation. AgNPs sulfidized with HA showed surface potentials closer to that of HA. Sulfidation resulted in the formation of silver sulfide and both core-shell structure and heterogeneous sulfidation patterns were observed. The S/Ag ratio was found to be the dominant factor in the sulfidation process while different conditions of HA exposure barely influenced the extent of sulfidation. Finally, the self-aggregation and granular media deposition of PVP-AgNPs after HA exposure and sulfidation were investigated. It was found that HA exposure modified the original PVP capping via adsorption and/or ligand exchange and sulfidation stripped the PVP from the particle surface as a result of the formation of silver sulfide. Sulfidation thereby reduced the stability of PVP-AgNPs in self-aggregation and enhanced the mobility of AgNPs in granular media filtration. Without unbound macromolecules in the background solution, polymer on the particle surface largely prevented self-aggregation but allowed favorable clean bed deposition due to bridging if the polymer had high affinity to the collector surface. Our study shows that though environmental transformations (e.g., HA exposure and sulfidation) complicate the fate and transport of AgNPs in water, as long as the AgNPs are effectively destabilized, they either self-aggregate or deposit on to collector surfaces. The “old” process of granular media filtration can still control the fate of the emerging pollutant of AgNPs.Item Microfluidics for bioanalytical research : transitioning into point-of-care diagnostics(2014-12) Scida, Karen; Crooks, Richard M. (Richard McConnell)In this dissertation, three different microfluidic devices with bioanalytical applications are presented. From chapter to chapter, the bioanalytical focus will gradually become the development of a point-of-care sensor platform able to yield a reliable and quantitative response in the presence of the desired target. The first device consists of photolithographically-patterned gold on glass bipolar electrodes and PDMS Y-shaped microchannels for the controlled enrichment, separation from a mixture, and delivery of two charged dyes into separate receiving microchannels. The principle for the permanent separation of these dyes is based on the concept of bipolar electrochemistry and depended on the balancing/unbalancing of convective and electromigrating forces caused by the application of a potential bias, as well as the activation/deactivation of the bipolar electrodes. Two different bipolar electrode configurations are described and fluorescence is used to optimize their efficiency, speed, and cleanliness of delivery. The second device is a DNA sensor fabricated on paper by wax printing and folding to form 3D channels. DNA is detected by strand-displacement induced fluorescence of a single-stranded DNA. A multiplexed version of this sensor is also shown where the experiment results in “OR” and “AND” Boolean logic gate operations. In addition, the nonspecific adsorption of the reagents to cellulose is studied, demonstrating that significant reduction of nonspecific adsorption and increased sensitivity can be achieved by pre-treating the substrate with bovine serum albumin and by preparing all analyte solutions with spectator DNA. The third device, also made of paper, has a novel design and uses a versatile electrochemical detection method for the indirect detection of analytes via the direct detection of AgNP labels. A proof-of-concept experiment is shown where streptavidin-coated magnetic microbeads and biotin-coated AgNPs are used to form a composite model analyte. The paper device, called oSlip, and electrochemical method used are easily coupled so the resulting sensor has a simple user-device interface. LODs of 767 fM are achieved while retaining high reproducibility and efficiency. The fourth device is the updated version of the oSlip. In this case, the objective is to show the current progress and limitations in the detection of real analytes using the oSlip device. A sandwich-type immunoassay approach is used to detect human chorionic gonadotrophin (pregnancy hormone) present in human urine. Various optimization steps are performed to obtain the ideal reagent concentrations and incubation time necessary to form the immunocomposite in one step, that is, by mixing all reagents at the same time in the oSlip. Additionally, improvements to the electrochemical detection step are demonstrated.