Um dispositivo eletroquímico foi desenvolvido para a determinação simultânea de sulfametoxazol (SMX) e trimetoprim (TMP), utilizando voltametria de pulso diferencial e um eletrodo de carbono vítreo (GC) modificado com o compósito óxido de grafeno reduzido (rGO) e nanopartículas de prata (AgNPs), sintetizados por dois métodos: químico e o eletroquímico. A morfologia e o comportamento eletroquímico dos eletrodos GC modificados com os compósitos rGO/AgNPs (método químico) e rGO-AgNPs (método eletroquímico) foram caracterizados por microscopia eletrônica de varredura acoplada a um canhão de elétrons (FEG-SEM) e voltametria cíclica (CV). Essas técnicas demostraram que, nos dois métodos utilizados, o óxido de grafeno (GO) foi modificado com as AgNPs, e que o compósito sintetizado pelo método eletroquímico apresentou uma melhor dispersão das nanopartículas, resultando em um aumento da área superficial quando comparado ao compósito rGO/AgNPs. Assim, o eletrodo GC/rGO-AgNPs foi avaliado e otimizado na determinação simultânea de SMX e TMP e atingiu limites de detecção de 0,6 µmol L-1 para o SMX e 0,4 µmol L-1 para o TMP. O dispositivo eletroquímico proposto, GC/rGO-AgNPs, foi aplicado com sucesso na determinação simultânea de SMX e TMP em águas residuárias. / An electrochemical device was developed for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) using differential pulse voltammetry, and a glassy carbon electrode (GC) modified with the reduced graphene oxide composite (rGO) and silver nanoparticles (AgNPs), synthesized by two methods: chemical and electrochemical. The morphology and the electrochemical behavior of the GC electrode modified with composite rGO/AgNPs (chemical method) and rGO-AgNPs (electrochemical method) were characterized by scanning electron microscopy coupled to an electron gun (FEG-SEM) and cyclic voltammetry (CV). These techniques demonstrated that, in both methods, the graphene oxide (GO) was modified with AgNPs, and the composite synthesized by the electrochemical method showed a better dispersion of the nanoparticles, resulting in an increased surface area when compared to the composite rGO/ AgNPs. Thus, the GC/rGO-AgNPs electrode was evaluated and optimized for simultaneous determination of SMX and TMP and achieved detection limits of 0,6 µmol L-1 to SMX and 0,4 µmol L-1 for the TMP. The proposed electrochemical device, GC/rGO-AgNPS, was successfully applied for the simultaneous determination of SMX and TMP in wastewater.

The objective of this research was the development of an efficient method for the preparation of silver-polymer nanocomposites containing finely dispersed silver nanoparticles. The surface of nanosilver was functionalized by thiolation with 2-aminoethanethiol. Amino-modified nanosilver was covalently bonded to polyacrylic acid, biodegradable polymers like acid terminated polylactic acid, ester terminated poly(DL-lactide-co-glycolide) and acid terminated poly(DL lactide-co-glycolide) in the presence of diisopropylcarbodiimide by carbodiimide method. Esterification of the carboxyl groups of Ag-polyacrylic acid by hydrochloric acid in methanol resulted in the formation of a stable colloidal dispersion of Ag nanoparticles in the polymer matrix. It was observed that not just acid terminated polymers but also ester terminated polymers could react with functionalized nanosilver. This unusual reaction was due to the aminolysis of the ester bond in the polymer chain by the surface amino groups. Silver-polymer nanocomposites obtained with acid terminated polylactic acid and poly(DL-lactide-co-glycolide) contained highly dispersed nanosilver in the polymer matrix in comparison with the ester terminated poly(DL-lactide-co-glycolide). Chemical and structural characteristics of the obtained materials were studied by instrumental methods. Attained biodegradable materials confirmed X-ray contrast and bactericidal properties, which could be eventually used for biomedical applications.

This work attempted to detect chemical warfare agent (CWA) simulants via electrochemistry utilizing two approaches. The first approach consisted of a ferrocene (Fc) amino acid derivative film on Au surfaces. The molecule [(BocHN)Fc(CO)CSA]2 was electrodeposited onto Au microelectrodes through a SAu bond. Once immobilized, the Fc amino acid derivative was Boc deprotected allowing for the amino group to react with the target molecule. Detection of the target simulant was monitored by cyclic voltammetry (CV) while following the formal potential of the Fc molecule, which is influenced by its immediate electronic microenvironment. Reaction with either 1 mM diethyl cyanophosphonate (DECP) or 2 chloroethyl ethyl sulfide (2 CEES), both effectively simulants for the CWAs Tabun nerve agent and blistering sulfur mustard respectively, was not observed. However, detection of 1 mM acetyl chloride was achieved by observing a potential anodic shift from 217 ± 6 mV, for the Boc deprotected form, to 388 ± 7 mV for the reacted state of the molecule. The lack of reactivity with the Fc amino acid system was hypothesized as a kinetic issue.<p> In the second approach, the electrochemistry of gas generated naked Ag nanoparticles (NPs) deposited on indium tin oxide covered glass plates is compared to bulk polycrystalline Ag. The nano specific electrochemistry of Ag NPs has been identified and includes the preferential formation of â oxides. In 100 mM KOH supporting electrolyte, disruption of â oxide formation is exploited to test for the presence of 1 mM DECP resulting in the dissolution of Ag via cyanide complexes leading to a CV signal decrease. While in 8.0 M KOH, â oxide formation is enhanced leading to testing capabilities for 1 mM 2 CEES resulting in the disappearance of the â oxide peak and the appearance of surface oxide peak during CV. Analogous electrochemistry is not observed on polycrystalline bulk Ag.

Dopamine is a neurotransmitter found in central nerve system which has a vital role for human health. Dopamine oxidation in body is an important issue since it may form reactive metabolites which can be toxic to the cell. Surface-enhanced Raman scattering (SERS) is currently recognized as one of the most sensitive spectroscopic tools, which can be exploited for ultrasensitive chemical and biological detection, addition to providing structural information on the systems of interest. SERS of dopamine displays three strong bands at 1269, 1331 and 1479 cm-1. These bands are the signature of dopamine molecule. The most intense band at 1479 cm-1 is contributed mainly from stretching of the carbon-carbon bond to which the oxygens are attached. A bidentate silver-dopamine complex or in general bidentate metal-dopamine complex formation is required for the SERS detection of dopamine and other catecholamines. In other words, for acquiring the characteristic dopamine SERS signature, both of the catechol oxygens should take a part in the adsorption of dopamine to the silver metal surface which is used as a SERS substrate. Therefore, the reactivity of different oxidation forms of dopamine for the formation of bidentate silver-dopamine complex was investigated by obtaining their SERS spectra and following the characteristic C-C ring vibration at 1479 cm-1. Dopamine oxidation was carried out electrochemically, utilizing platinum and silver electrodes as working electrode. Oxidation products formed were identified with UV-vis Spectrometer. Also, silver metal ions were used to oxidize dopamine, leading to formation silver nanoparticles. Dopamine functionalized silver nanoparticles were characterized by Scanning Electron Microscope, Transmission Electron Microscope, UV-vis Spectrometer. Surface- enhanced Raman spectra of polydopamine on the surface of synthesized silver nanoparticles and the electrodeposited dopamine on the porous surface of silver electrode were also obtained.

With the industry striving for smaller devices, new technologies are developed to further miniaturize electronics devices. To this end, realization of 3D/non-planar interconnects, which aim at miniaturizing the interconnects formed between components on the same device, has attracted many researchers. This thesis focuses on a feasibility analysis for developing non-planar interconnects on various flexible substrates using laser assisted maskless microdeposition (LAMM), which is a pressure-less process. There are two types of flexible substrates that are used: double-sided copper substrates separated by a layer of polyethylene terephthalate (PET) as well as a polyethylene terephthalate flexible substrate with surface-mounted resistors. For both substrates, multiple types of experiments were conducted to discover procedures which result in the highest rate of success for forming conductive interconnects. Optimal process parameters and deposition techniques were determined after multiple experiments. After experiments were completed, the resultant substrates were subject to various characterization methodologies including optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and profilometery. The results of these methodologies are documented in this thesis. After many types of experiments involving substrate manipulation of the double-sided copper substrates, it was shown that the silver nano-particles were more likely to form a conductive interconnect when a polished slant was fabricated on the substrate. Many deposition patterns were used for the flexible substrates with surface-mounted resistors. Of these patterns, the two patterns, the ‘zigzag’ and ‘dot solder’ patterns, proved to have a much higher success rate for creating conductive interconnects compared to the other patterns. During this study, the results of the experiments using the LAMM process show that this technology has great potential for creating non-planar interconnects on flexible substrates. The experiments however suggest that the process is very sensitive to the material composition and process parameters. As such, with a small change in parameters, the 3D interconnects can fail to be produced. It was also observed that the possibility of silver interconnect fractures is higher where dissimilar materials with different thermal expansion rates are used for the underlying substrates.

This work attempted to detect chemical warfare agent (CWA) simulants via electrochemistry utilizing two approaches. The first approach consisted of a ferrocene (Fc) amino acid derivative film on Au surfaces. The molecule [(BocHN)Fc(CO)CSA]2 was electrodeposited onto Au microelectrodes through a SAu bond. Once immobilized, the Fc amino acid derivative was Boc deprotected allowing for the amino group to react with the target molecule. Detection of the target simulant was monitored by cyclic voltammetry (CV) while following the formal potential of the Fc molecule, which is influenced by its immediate electronic microenvironment. Reaction with either 1 mM diethyl cyanophosphonate (DECP) or 2 chloroethyl ethyl sulfide (2 CEES), both effectively simulants for the CWAs Tabun nerve agent and blistering sulfur mustard respectively, was not observed. However, detection of 1 mM acetyl chloride was achieved by observing a potential anodic shift from 217 ± 6 mV, for the Boc deprotected form, to 388 ± 7 mV for the reacted state of the molecule. The lack of reactivity with the Fc amino acid system was hypothesized as a kinetic issue.<p> In the second approach, the electrochemistry of gas generated naked Ag nanoparticles (NPs) deposited on indium tin oxide covered glass plates is compared to bulk polycrystalline Ag. The nano specific electrochemistry of Ag NPs has been identified and includes the preferential formation of â oxides. In 100 mM KOH supporting electrolyte, disruption of â oxide formation is exploited to test for the presence of 1 mM DECP resulting in the dissolution of Ag via cyanide complexes leading to a CV signal decrease. While in 8.0 M KOH, â oxide formation is enhanced leading to testing capabilities for 1 mM 2 CEES resulting in the disappearance of the â oxide peak and the appearance of surface oxide peak during CV. Analogous electrochemistry is not observed on polycrystalline bulk Ag.

<p>Background: Silver nanoparticles (AgNPs) act as antimicrobials by releasing monovalent silver (Ag+) and are increasingly used in consumer products, thus elevating exposures in human and environmental populations. Materials and Methods: We evaluated Ag+ in a standard model of neuronal cell replication and differentiation, and then determined whether there were similar effects of the ion in vivo using zebrafish. Next, we compared Ag+ and AgNP exposures in the same two models and incorporated the effects of particle coating, size and composition. Conclusions: This work is the first to show that both Ag+ and AgNPs are developmental neurotoxicants in vitro and in vivo. Moreover, although both the soluble ion and the particles impair measures of neurodevelopment, the outcomes and underlying mechanisms of each toxicant are often wholly distinct. Superimposed on the dichotomies between Ag+ and AgNP exposures are clear effects of particle coating, size and composition that will necessitate evaluation of individual AgNP types when considering potential environmental and human health effects. The results presented here provide hazard identification that can help isolate the models and endpoints necessary for developing a risk assessment framework for the growing use of AgNPs.</p> / Dissertation

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. / text

With the industry striving for smaller devices, new technologies are developed to further miniaturize electronics devices. To this end, realization of 3D/non-planar interconnects, which aim at miniaturizing the interconnects formed between components on the same device, has attracted many researchers. This thesis focuses on a feasibility analysis for developing non-planar interconnects on various flexible substrates using laser assisted maskless microdeposition (LAMM), which is a pressure-less process. There are two types of flexible substrates that are used: double-sided copper substrates separated by a layer of polyethylene terephthalate (PET) as well as a polyethylene terephthalate flexible substrate with surface-mounted resistors. For both substrates, multiple types of experiments were conducted to discover procedures which result in the highest rate of success for forming conductive interconnects. Optimal process parameters and deposition techniques were determined after multiple experiments. After experiments were completed, the resultant substrates were subject to various characterization methodologies including optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and profilometery. The results of these methodologies are documented in this thesis. After many types of experiments involving substrate manipulation of the double-sided copper substrates, it was shown that the silver nano-particles were more likely to form a conductive interconnect when a polished slant was fabricated on the substrate. Many deposition patterns were used for the flexible substrates with surface-mounted resistors. Of these patterns, the two patterns, the ‘zigzag’ and ‘dot solder’ patterns, proved to have a much higher success rate for creating conductive interconnects compared to the other patterns. During this study, the results of the experiments using the LAMM process show that this technology has great potential for creating non-planar interconnects on flexible substrates. The experiments however suggest that the process is very sensitive to the material composition and process parameters. As such, with a small change in parameters, the 3D interconnects can fail to be produced. It was also observed that the possibility of silver interconnect fractures is higher where dissimilar materials with different thermal expansion rates are used for the underlying substrates.

>Magister Scientiae - MSc / One-dimensional silicon nanowires (SiNWs) are promising building blocks for solar cells as they provide a controlled, vectorial transport route for photo-generated charge carriers in the device as well as providing anti-reflection for incoming light. Two major approaches are followed to synthesise SiNWs, namely the bottom-up approach during vapour-liquid-solid mechanism which employs chemical vapour deposition techniques. The other method is the top-down approach via metal assisted chemical etching (MaCE). MaCE provides a simple, inexpensive and repeatable process that yields radially and vertically aligned SiNWs in which the structure is easily controlled by changing the etching time or chemical concentrations. During MaCE synthesis, a crystalline silicon (c-Si) substrate covered with metal nanoparticles (catalyst) is etched in a diluted hydrofluoric acid solution containing oxidising agents. Since the first report on SiNWs synthesised via MaCE, various publications have described the growth during the MaCE process. However lingering questions around the role of the catalyst during formation, dispersion and the eventual diameter of the nanowires remain. In addition, very little information pertaining to the changes in crystallinity and atomic bonding properties of the nanowires post synthesis is known. As such, this study investigates the evolution of vertical SiNWs from deposited silver nanoparticles by means of in-depth electron microscopy analyses. Changes in crystallinity during synthesis of the nanowires are probed using x-ray diffraction (XRD) and transmission electron microscopy (TEM). Deviations in the optical properties are quantified using optical reflectivity measurements by employing ultraviolet-visible (UV-Vis) spectroscopy, whereas the bonding configurations of the nanowires are probed by Raman and Fourier transforms infrared spectroscopy. Diameters of 50 – 200 nm vertical SiNWs were obtained from scanning electron micrographs and nanowires lengths linearly increased with etching time duration from about 130 nm after 30 seconds to over 15 μm after 80 minutes. No diameter modulations along nanowires axial direction and rough nanowires apexes were observed for nanowires obtained at longer etching times. These SiNWs remained crystalline as their bulk single crystalline Si wafers but had a thin amorphous layer on the surface, findings confirmed by TEM, XRD and Raman analysis. Nanowires were found to be partially passivated with oxygen with small traces of hydrogen termination, confirmed with infrared absorption studies. Finally, low optical reflection of less than 10% over visible range compared to an average of 30% for bulk Si were measured depicting an antireflective ability required in silicon solar cells.