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.

<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

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.

MESQUITA, Ricardy Leonam Pontes. Síntese de nanopartículas de prata através de ultrassom utilizando galactomanana. 2016. 94 f. Dissertação (Mestrado em química)- Universidade Federal do Ceará, Fortaleza-CE, 2016. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-28T17:12:54Z No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-08-02T14:38:19Z (GMT) No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) / Made available in DSpace on 2016-08-02T14:38:19Z (GMT). No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) Previous issue date: 2016 / Silver nanoparticles (NPAg) have attracted considerable interest in the context of research in recent years due to numerous applications, such as a bactericide, sensors and catalysts. In this paper the use of galactomannan of fava danta (GFD) in obtaining NPAg by ultrasonic method was studied based on the principles of green chemistry without the use of conventional chemical reducing agent. This study aimed to evaluate the ultrasound employment in NPAg synthesis GFD solutions. The NPAg were obtained with the aid of an ultrasonic probe using AgNO3 aqueous solution in concentrations of 10, 40 and 100 mmol / L. The galactomannan in aqueous solution (0,032%, 0,32% and 0,0032% w/ v) was used as stabilizer of NPAg. The synthesis occurred at varying pH (10, 11, 12) and temperature (15, 25 and 35 °C). The characterizations were performed using techniques such as gel permeation chromatography (GPC), nuclear magnetic resonance of hydrogen (NMR1H), spectrophotometry UV-Vis, dynamic light scattering (DLS) and scanning electron microscopy (SEM). UV-Vis analysis for colloids formed during the synthesis at the three concentrations showed the emergence of the plasmon band (around 400 nm) suggesting the formation of NPAg. It was observed faster kinetic profile for concentration systems 10 mmol/ L AgNO3. The pH 11 and 12 provided the best conditions for synthesis of NPAg. The different concentrations of synthetic GFD showed satisfactory results, but the formed colloid concentration 0,0032% w/ v showed no stability. Two of the synthesized colloids were selected FDAg 10/12/25 and FDAg 100/12/25, to submit the study to estimate size during the time of formation of NPAg as were also objects of analysis by electron microscopy scan. DLS was evidenced by the two colloids have decreased the size NPAg during the synthesis time, reaching average sizes near 10 to 4 nm for FDAg 10/12/25 and FDAg 100/12/25 respectively. Monitoring the polysaccharide degradation by GPC analysis was conducted and it was observed the decrease in distribution of the molar masses of the same of 6,65 x 106 to 3,11 x 104 g/ mol during the degradation process. The mannose/ galactose ratio was observed for the GFD, from 1:1,23 to GFD unmodified to 1:2,14 for the GFD degraded in 420 minutes. Thus, this study showed that the ultrasonic path in conjunction with the use of the galactomannan of fava danta in aqueous solution provides a versatile synthetic route for NPAg with good stability. / Nanopartículas de prata (NPAg) têm atraído bastante interesse no âmbito da pesquisa durante os últimos anos devido às inúmeras aplicações, tais como agente bactericida, sensores e catalisadores. Neste trabalho o uso de galactomanana da fava danta (GFD) na obtenção das NPAg por método ultrassônico foi estudado com base nos princípios da química verde sem a utilização de redutores químicos convencionais. Este estudo teve como objetivo, avaliar o emprego do ultrassom na síntese de NPAg em soluções de GFD. As NPAg foram obtidas com auxílio de uma sonda ultrassônica, utilizando solução aquosa de AgNO3 nas concentrações 10, 40 e 100 mmol/L. A galactomanana em solução aquosa (0,032%, 0,32% e 0,0032% m/v) foi utilizada como estabilizante das NPAg. As sínteses ocorreram com variação de pH (10, 11 e 12) e de temperatura (15, 25 e 35 °C). As caracterizações foram realizadas através de técnicas como Cromatografia de permeação em gel (GPC), Ressonância magnética nuclear de hidrogênio (RMN 1H), Espectrofotometria UV-Vis, Espalhamento de luz dinâmico (DLS) e Microscopia eletrônica de varredura (MEV). As análises de UV-Vis para os coloides formados durante as sínteses nas três concentrações mostraram o surgimento da banda de plasmon (em torno de 400 nm) evidenciando a formação das NPAg. Observou-se perfil cinético mais rápido para os sistemas de concentração 10 mmol/L de AgNO3. Os valores de pH 11 e 12 proporcionaram as melhores condições de síntese das NPAg. As diferentes concentrações de GFD apresentaram resultados de síntese satisfatórios, porém o coloide formado em concentração 0,0032% m/v não apresentou estabilidade. Dois dos coloides sintetizados foram selecionados, FDAg 10/12/25 e FDAg 100/12/25, a se submeterem a estudo para estimativa de tamanho durante todo o tempo de formação das NPAg, assim como também foram objetos de análise por Microscopia eletrônica de varredura. Por DLS foi evidenciado que os dois coloides tiveram diminuição de tamanho das NPAg no decorrer do tempo de síntese, atingindo tamanhos médios próximos de 10 e 4 nm para FDAg 10/12/25 e FDAg 100/12/25 respectivamente. Foi realizado o acompanhamento da degradação do polissacarídeo através de análise por GPC, tendo sido observado a diminuição da distribuição das massas molares do mesmo de 6,65 x 106 para 3,11 x 104 g/mol durante o processo de degradação. A razão manose/galactose foi verificada para a GFD, passando de 1:1,23 para a GFD não modificada para 1:2,14 para a GFD degradada em 420 minutos. Sendo assim, este estudo mostrou que a via ultrassônica em conjunto com a utilização da galactomanana da fava danta em solução aquosa proporciona uma rota sintética bastante versátil para as NPAg com boa estabilização.

The field of nanoecotoxicology has been pioneered in recent years as concern grows in response to the potential environmental hazards of engineered nanoparticle release. Silver nanoparticle (AgNP) release through induction into commercial products as an antimicrobiont is of particular interest. Plausible routes of AgNPs to reach aquatic systems and their biological impacts have been investigated, but none have addressed the potential remediation of these waters using the heavy metal accumulating fern Azolla caroliniana. This study employed biological staining techniques and fluorescence microscopy to identify oxidative stress, wounding responses of cell wall and membrane, and cell death of A. caroliniana roots to assess the capability of this plant to withstand AgNP exposure. Two concentrations series were applied, 0-1.0ppm and 0-10.0ppm for 1, 3, 5 days after transfer (DAT), 0ppm being a control. Oxidative stress, measured in production of non-specific ROS, increased in a dose-dependent manner with increasing AgNP concentration. Callose (1,3-β-glucan) was deposited in response to potential cell wall damage and was also observed to be elevated in a dose-dependent manner. Cell vitality appeared from a general decline in fluorescence of nucleic content to visual nuclei lysis. Statistically significant and severe responses to AgNPs was observed at 1 DAT but recovery could be seen at 3~5 DAT. In sum, these data suggest a toxicity threshold of 1.0ppm at which A. caroliniana roots can mediate exposure.

abstract: With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane. This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts. The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2017

Universidade Federal do Cearà / Silver nanoparticles (NPAg) have attracted considerable interest in the context of research in recent years due to numerous applications, such as a bactericide, sensors and catalysts. In this paper the use of galactomannan of fava danta (GFD) in obtaining NPAg by ultrasonic method was studied based on the principles of green chemistry without the use of conventional chemical reducing agent. This study aimed to evaluate the ultrasound employment in NPAg synthesis GFD solutions. The NPAg were obtained with the aid of an ultrasonic probe using AgNO3 aqueous solution in concentrations of 10, 40 and 100 mmol / L. The galactomannan in aqueous solution (0,032%, 0,32% and 0,0032% w/ v) was used as stabilizer of NPAg. The synthesis occurred at varying pH (10, 11, 12) and temperature (15, 25 and 35 ÂC). The characterizations were performed using techniques such as gel permeation chromatography (GPC), nuclear magnetic resonance of hydrogen (NMR1H), spectrophotometry UV-Vis, dynamic light scattering (DLS) and scanning electron microscopy (SEM). UV-Vis analysis for colloids formed during the synthesis at the three concentrations showed the emergence of the plasmon band (around 400 nm) suggesting the formation of NPAg. It was observed faster kinetic profile for concentration systems 10 mmol/ L AgNO3. The pH 11 and 12 provided the best conditions for synthesis of NPAg. The different concentrations of synthetic GFD showed satisfactory results, but the formed colloid concentration 0,0032% w/ v showed no stability. Two of the synthesized colloids were selected FDAg 10/12/25 and FDAg 100/12/25, to submit the study to estimate size during the time of formation of NPAg as were also objects of analysis by electron microscopy scan. DLS was evidenced by the two colloids have decreased the size NPAg during the synthesis time, reaching average sizes near 10 to 4 nm for FDAg 10/12/25 and FDAg 100/12/25 respectively. Monitoring the polysaccharide degradation by GPC analysis was conducted and it was observed the decrease in distribution of the molar masses of the same of 6,65 x 106 to 3,11 x 104 g/ mol during the degradation process. The mannose/ galactose ratio was observed for the GFD, from 1:1,23 to GFD unmodified to 1:2,14 for the GFD degraded in 420 minutes. Thus, this study showed that the ultrasonic path in conjunction with the use of the galactomannan of fava danta in aqueous solution provides a versatile synthetic route for NPAg with good stability. / NanopartÃculas de prata (NPAg) tÃm atraÃdo bastante interesse no Ãmbito da pesquisa durante os Ãltimos anos devido Ãs inÃmeras aplicaÃÃes, tais como agente bactericida, sensores e catalisadores. Neste trabalho o uso de galactomanana da fava danta (GFD) na obtenÃÃo das NPAg por mÃtodo ultrassÃnico foi estudado com base nos princÃpios da quÃmica verde sem a utilizaÃÃo de redutores quÃmicos convencionais. Este estudo teve como objetivo, avaliar o emprego do ultrassom na sÃntese de NPAg em soluÃÃes de GFD. As NPAg foram obtidas com auxÃlio de uma sonda ultrassÃnica, utilizando soluÃÃo aquosa de AgNO3 nas concentraÃÃes 10, 40 e 100 mmol/L. A galactomanana em soluÃÃo aquosa (0,032%, 0,32% e 0,0032% m/v) foi utilizada como estabilizante das NPAg. As sÃnteses ocorreram com variaÃÃo de pH (10, 11 e 12) e de temperatura (15, 25 e 35 ÂC). As caracterizaÃÃes foram realizadas atravÃs de tÃcnicas como Cromatografia de permeaÃÃo em gel (GPC), RessonÃncia magnÃtica nuclear de hidrogÃnio (RMN 1H), Espectrofotometria UV-Vis, Espalhamento de luz dinÃmico (DLS) e Microscopia eletrÃnica de varredura (MEV). As anÃlises de UV-Vis para os coloides formados durante as sÃnteses nas trÃs concentraÃÃes mostraram o surgimento da banda de plasmon (em torno de 400 nm) evidenciando a formaÃÃo das NPAg. Observou-se perfil cinÃtico mais rÃpido para os sistemas de concentraÃÃo 10 mmol/L de AgNO3. Os valores de pH 11 e 12 proporcionaram as melhores condiÃÃes de sÃntese das NPAg. As diferentes concentraÃÃes de GFD apresentaram resultados de sÃntese satisfatÃrios, porÃm o coloide formado em concentraÃÃo 0,0032% m/v nÃo apresentou estabilidade. Dois dos coloides sintetizados foram selecionados, FDAg 10/12/25 e FDAg 100/12/25, a se submeterem a estudo para estimativa de tamanho durante todo o tempo de formaÃÃo das NPAg, assim como tambÃm foram objetos de anÃlise por Microscopia eletrÃnica de varredura. Por DLS foi evidenciado que os dois coloides tiveram diminuiÃÃo de tamanho das NPAg no decorrer do tempo de sÃntese, atingindo tamanhos mÃdios prÃximos de 10 e 4 nm para FDAg 10/12/25 e FDAg 100/12/25 respectivamente. Foi realizado o acompanhamento da degradaÃÃo do polissacarÃdeo atravÃs de anÃlise por GPC, tendo sido observado a diminuiÃÃo da distribuiÃÃo das massas molares do mesmo de 6,65 x 106 para 3,11 x 104 g/mol durante o processo de degradaÃÃo. A razÃo manose/galactose foi verificada para a GFD, passando de 1:1,23 para a GFD nÃo modificada para 1:2,14 para a GFD degradada em 420 minutos. Sendo assim, este estudo mostrou que a via ultrassÃnica em conjunto com a utilizaÃÃo da galactomanana da fava danta em soluÃÃo aquosa proporciona uma rota sintÃtica bastante versÃtil para as NPAg com boa estabilizaÃÃo.

>Magister Scientiae - MSc / The global lack of clean water for human sanitation and other purposes has become an emerging dilemma for human beings. The presence of organic pollutants in wastewater produced by textile industries, leather manufacturing and chemical industries is an alarming matter for a safe environment and human health. For the last decades, conventional methods have been applied for the purification of water but due to industrialization these methods fall short. Advanced oxidation processes and their reliable application in degradation of many contaminants have been reported as a potential method to reduce and/or alleviate this problem. Lately, it has been assumed that incorporation of some metal nanoparticles such as magnetite nanoparticles as photocatalyst for Fenton reaction could improve the degradation efficiency of contaminants. Core/shell nanoparticles, are extensively studied because of their wide applications in the biomedical, drug delivery, electronics fields and water treatment. The current study is centred on the synthesis of silver-doped Fe₃O₄/SiO₂/TiO₂ photocatalyst. Magnetically separable Fe₃O₄/SiO₂/TiO₂ composite with core–shell structure were synthesized by the deposition of uniform anatase TiO₂ NPs on Fe₃O₄/SiO₂ by using titanium butoxide (TBOT) as titanium source. Then, the silver is doped on TiO₂ layer by hydrothermal method. Integration of magnetic nanoparticles was suggested to avoid the post separation difficulties associated with the powder form of the TiO₂ catalyst, increase of the surface area and adsorption properties. Lastly and most importantly magnetic nanoparticles upsurge the production of hydroxyl groups or reduced charge recombination. The a synthesized catalysts were characterized using Transmission Electron Microscopy, X-ray Diffraction; Infra-red Spectroscopy, Scanning Electron Microscope and Energy Dispersive Spectroscopy. Other characterization techniques includeVibrating Sample Magnetometry, Brunauer Emmett Teller analysis and Thermogravimetric analysis. The average size of the particles size is 72 nm. Furthermore the photocatalytic performances of the magnetic catalysts were assessed in comparison with that commercial titanium dioxide for the degradation of methylene blue using photochemical reactor under ultra violet light. The results showed that the photocatalytic activity was enhanced using Fe₃O₄/SiO₂/TiO₂ and Ag-Fe₃O₄/SiO₂/TiO₂ compared with that for Fe₃O₄, commercial titanium dioxide powder.

>Magister Scientiae - MSc / Water is essential for life, yet access to safe drinking water is still a major concern worldwide due to waterborne diseases. The current study proposes silver nanoparticles (AgNPs) as an antibacterial agent. Silver nanoparticles were synthesised using different reductants and stabilisers, and the resulting structures were characterised with Ultra-violet visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) analysis. The antibacterial properties of the AgNPs were tested against a panel of 5 indicator organisms: Cupriavidus metallidurans, Staphylococcus epidermidis, Mycobacterium smegmatis, Bacillus cereus and a multi-drug resistant Escherichia coli 1699. Spherical AgNPs that absorbed at around 400 nm, with diameters ranging between 18.8-26.4 nm or 5.4-13.1 nm were prepared by ascorbic acid or sodium borohydride respectively. The optimum processing conditions that produced 6±1.8 nm spherical nanoparticles included maintaining the temperature at 0 ⁰C, the pH at 9.78 and the NaBH4/Ag/PVP ratio at 16:1:10. Exposing AgNPs to light for 6 hours did not alter the particle size rather it changed the particles shape from spherical to icosahedral. Stirring caused particles to agglomerate, however, no agitation resulted in the formation of irregular structures of different sizes. Sensitivity to the AgNPs ranged between 25 % and 100 % reduced bacterial growth depending on the strains used and the concentration of the AgNPs. The Gram negative bacteria were more sensitive to AgNPs than Gram positive bacteria. However silver ions were more toxic than AgNPs for all but one of the strains tested, B. cereus was completely resistant to both Ag+ and AgNPs. C. metallidurans and E.coli (1699) showed a dose dependent sensitivity to AgNPs and the minimum inhibitory concentrations were established at 50 and 20 mg/L AgNPs respectively. C. metallidurans and E.coli (1699) were also eradicated by 10 mg/L Ag+. The E. coli TEM images showed accumulation of AgNPs within the cells, cell shrinking and leakage of cellular components. This suggests that AgNPs have a similar toxicity effect on bacterial cells as Ag+.