Over the years, megasonic energy has been widely used in the semiconductor industry for effective particle removal from surfaces after chemical mechanical planarization (CMP) processes. As a sound wave propagates through a liquid medium, it generates two effects, namely, acoustic streaming and acoustic cavitation. Acoustic streaming refers to time independent motion of liquid due to viscous attenuation, while cavitation arises from the bubble activity generated due to the difference in the pressure field of the propagating wave. Cavitation can be classified into two categories, (1) stable and (2) transient cavitation. When a bubble undergoes continuous oscillations over repeated cycles it is known to exhibit stable cavitation, while a sudden collapse is referred to as transient cavitation. Due to the rapid implosion of the transient cavity, drastic conditions of temperature (5,000-10,000 K) and pressure (hundreds of bars) are generated within and surrounding the bubble. If this phenomenon occurs close to the substrate, it causes damage to the sub-micron features. In this study, emphasis has been laid on understanding acoustic cavitation as it is critical to achieving high cleaning efficiency without any feature damage. The research work described in this dissertation has been divided into three sections. In the first part of the dissertation, the development of a novel sono-electrochemical technique for removal of sub-micron (300 nm) silica particles from conductive surfaces (Ta) has been discussed. The technique employs megasonic field at low pulse time and duty cycle in conjunction with an applied electrical field for achieving superior particle removal efficiency (PRE). In order to demonstrate the effectiveness of the sono-electrochemical technique, cleaning studies were conducted using 300 nm silica particles both in the presence and absence of an applied electrical field in air and argon saturated solutions. In the presence of the megasonic field (0.5 W/cm², 10% duty cycle, 5ms pulse time) alone, about 55% PRE was observed in Ar saturated DI water, while in the presence of the sono-electrochemical field (-1.5V vs Ag/AgCl (sat. KCl)), about 80% PRE was measured. The enhancement in particle removal efficiency was attributed to oscillating hydrogen bubbles formed from water reduction in close vicinity of the tantalum surface, that grow to a resonant size under suitable acoustic conditions and likely cause removal of particles. Interestingly, increasing the applied potential to -2V (vs Ag/AgCl (sat. KCl)) enhanced the particle removal efficiency to about 100%. Investigations were also performed in solutions containing 10 mM potassium chloride (KCl). The results revealed that even at low applied potentials of -1.5V, almost complete particle removal was achieved. This improvement in PRE was attributed to a combined effect of microstreaming and electro-acoustic forces. The results revealed that almost complete removal of particles could be achieved at low power density and duty cycle when a sound field at 1 MHz is used in conjunction with electrochemistry. The second study focuses on the effect of acoustic frequency and transducer power density for the development of a damage-free megasonic cleaning process. Here, an effort was made to characterize cavitation activity at acoustic frequencies of 1, 2 and 3 MHz by means of electrochemical, acoustic emission and fluorescence spectroscopy techniques. Studies conducted with a microelectrode using ferricyanide as an electroactive species showed that at 1 MHz and 2 W/cm², current peaks with a rise and fall time of about 30-50 ms and 80-120 ms were observed, respectively, which were indicative of transient cavitation behavior. Interestingly at higher frequencies (3 MHz), symmetric and oscillatory behavior in the current was observed. The rise and fall times were about 3 orders of magnitude lower at about 50 µs. This oscillatory behavior in the current at 3 MHz was attributed to the presence of stable cavities. Furthermore, hydrophone studies supported the microelectrode studies as they showed a reduction of about two orders of magnitude in the intensity of transient cavitation as frequency was increased from 1 to 3 MHz. Hydroxyl radical (OH*) capture measurements using terephthalate dosimetry corroborated the above results as they illustrated an order of magnitude decrease in OH* generation rate at 3 MHz compared to 1 MHz. These studies suggest that the use of higher megasonic frequencies may be more suitable for damage-free and effective cleaning of patterned surfaces in the semiconductor industry. In the last part of the dissertation, we investigate the effect of solution parameters on cavitation characteristics using a bicarbonate based alkaline chemical cleaning formulation that has been previously demonstrated to be beneficial in achieving effective megasonic cleaning and low damage. The results of this study revealed that in the presence of ammonia (NH₃) or carbonate/bicarbonate ions at concentrations greater than 75 mM or 200 mM respectively, the measured rate of generation of hydroxyl radicals at 1 MHz and 2 W/cm² was significantly reduced. The lower rate of OH· was attributed to scavenging of radicals in these solutions and additionally due to reduced transient cavitation in ammonia solutions. Hydroxyl radical measurements at higher power density of 8 W/cm² showed that carbonate ions were better scavengers of hydroxyl radicals than bicarbonate ions. The study on the effect of bulk solution temperature illustrated that the rate of generation of OH· increased with increase in temperature from 10 to 30 °C suggesting enhanced transient cavitation at higher temperatures (in the investigated range). The use of optimum concentration of ammonia or carbonates ions in cleaning formulation and bulk solution temperature would likely provide desired cleaning with minimum damage.

Established techniques for the detection of pathogens, such as bacteria and viruses, require long timeframes for culturing. State of the art biosensors rely on the diffusion of the target analyte to the sensor surface. AC electric fields can be exploited to enhance the sampling of pathogens and concentrate them at specific locations on the sensor surface, thus overcoming these bottlenecks. AC electrokinetic effects like the dielectrophoretic force and electrothermal flows apply forces on the particle and the bulk fluid, respectively. While dielectrophoresis forces pathogens towards a target location, electrothermal flows circulates the fluid, thus replenishing the local concentration. Numerical simulations and experimental proof of principle demonstrate how AC electrokinetics can be used to collect model bioparticles on an antibody functionalized selective surface from a heterogeneous solution having physiologically relevant conductivity. The presence of parallel channels in a quadrupolar microelectrode design is identified as detrimental during the negative dielectrophoretic collection of bioparticles at the centre of the design while simultaneously providing secondary concentration points. These microelectrodes were incorporated onto the surface of a novel cantilever design for the rapid positive dielectrophoretic collection of Escherichia coli bacteria and enabled the subsequent detection of the bacteria by measuring the shift in the resonance frequency of the cantilever. Finally, a proof of principle setup for a Raman coupled, AC electrokinetically enhanced sampling and detection of viruses is shown where the presence of M13 phages are identified on a selective antibody functionalized surface using Raman spectroscopy. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-01-30 19:23:48.958

This research focuses on the detection and characterization of cells using impedance-based techniques to understand the behavior and response of cells to internal/environmental changes. In combination with impedimetric sensing techniques, the biosensors in this work allow rapid, label-free, quantitative measurements and are very sensitive to changes in environment and cell morphology. The biosensor design and measurement setup is optimized to detect and differentiate cancer cells and healthy (normal) cells. The outcome of this work will provide a foundation for enhanced 3-dimensional tumor analysis and characterization; thus creating an avenue for earlier cancer detection and reduced healthcare costs. The magnitude of cancer-related deaths is a result of late-diagnosis and the fact that cancer is challenging to treat, due to the non-uniform nature of the tumor. In order to characterize and treat individual cells based on their malignant potential, it is important to have a measurement technique with enhanced spatial resolution and increased sensitivity. This requires the study of individual or small groups of cells that make up the entire tissue mass. The overall objective of this research is to optimize a microelectrode biosensor and obtain statistically relevant data from a cell culture using an independent multi-electrode design. This would provide a means to explore the feasibility of electrically characterizing cells with greater accuracy and enhanced sensitivity.

We have developed a high-throughput system of closed-loop electrical stimulation and optical recording that facilitates the rapid characterization of extracellular stimulus-evoked neural activity. The ability to selectively stimulate a neuron is a defining characteristic of next-generation neural prostheses. Greater stimulus control and differential activation of specific neuronal populations allows for prostheses that better mimic their biological counterparts. In our system, we deliver square current pulses using a microelectrode array; automated real-time image processing of high-speed digital video identifies the neuronal response; and a feedback controller alters the applied stimulus to achieve a targeted response. The system controller performs directed searches within the strength-duration (SD) stimulus parameter space to build probabilistic neuronal activation curves. An important feature of this closed-loop system is a reduction in the number of stimuli needed to derive the activation curves when compared to the more commonly used open-loop system: this allows the closed-loop system to spend more time probing stimulus regions of interest in the multi-parameter waveform space, facilitating high resolution analysis. The stimulus-evoked activation data were well-fit to a sigmoid model in both the stimulus strength (current) and duration (pulse width) slices through the waveform space. The 2-D analysis produced a set of probability isoclines corresponding to each neuron-electrode pairing, which were fit to the SD threshold model described by Lapique (1907). We show that stimulus selectivity within a given neuron pair is possible in the one-parameter search space by using multiple stimulation electrodes. Additionally, by applying simultaneous stimuli to adjacent electrodes, the interaction between stimuli alters the neuronal activation threshold. The interaction between simultaneous multi-electrode multi-parameter stimulus waveforms creates an opportunity for increased stimulus selectivity within a population. We demonstrated that closed-loop imaging and micro-stimulation technology enable the study of neuronal excitation across a large parameter space, which is requisite for controlling neuronal activation in next generation clinical solutions.

Embryonic stem cells (ESCs) are being considered as a cell source for cardiac regeneration because of their potency and availability. We studied the electrophysiological implications using co-cultures of ESCs and neonatal rat ventricular myocytes (NRVM) grown on a multi-electrode array (MEA). To mimic expected engraftment rates 5% mouse ESCs were co-cultured with NRVMs. Comparing cultures without and with 5% ESCs at 4 days, the mean bipolar field potential duration (FPD) of NRVMs increased from 26.3 ± 2.2 ms (n=10) to 44.3 ± 6.2 ms (n=9; p < 0.05), the interspike interval (ISI) increased from 358.3 ± 62.8 ms (n=10) to 947.8 ± 214.6 ms (n=7; p < 0.01), and conduction velocity (CV) decreased from 14.2 ± 1.3 cm/s (n=8) to 4.6 ± 1.2 cm/s (n=5; p < 0.01). To evaluate whether ESC were having direct or paracrine effects on NRVMs, media conditioned by 3x106 ESCs for 24 hr was diluted 1:1 with fresh media and then introduced to NRVM cultures on the day of plating. Conditioned media was changed daily and altered mean FPD, ISI, and CV to 46.1 ± 7.8 ms, ISI to 682.0 ± 128.5 ms, and 4.2 ± 0.4 cm/s (n=8; p < 0.01 for each measure), respectively at 4 days. However, changes were not seen in media that was incubated for 24hrs and diluted 1:1 with fresh media and introduced to NRVM cultures in a similar fashion (n=7; p > 0.05). Slowed CV is associated with increased arrhythmic risk and reports demonstrate an inverse relationship between CV and nonphosphorylated Cx43(NP-Cx43). Western blots for total Cx43 expression revealed a decrease in ratio of P-Cx43/NP-Cx43 in the 5% mouse ESCs and ESC conditioned media cultures as compared to controls (n=8; p < 0.01 for each). There was not significant increase in the total Cx43 expression (n=6; p > 0.05). Culturing ESCs with NRVMs resulted in a decreased ISI, prolonged FPD, and slowed CV of the co-cultures as compared to controls leading to pro-arrhythmic conditions. Similar effects on NRVMs were observed when applying media conditioned by ESCs, suggesting that the electrophysiological changes were mediated by soluble factors. The increase in NP-Cx43 leads to gap junction uncoupling being a potential mechanism for these arrhythmogenic substrates. Further research into preventing NP-Cx43 in cultures is currently underway.

abstract: There is a tremendous need for wireless biological signals acquisition for the microelectrode-based neural interface to reduce the mechanical impacts introduced by wire-interconnects system. Long wire connections impede the ability to continuously record the neural signal for chronic application from the rodent's brain. Furthermore, connecting and/or disconnecting Omnetics interconnects often introduces mechanical stress which causes blood vessel to rupture and leads to trauma to the brain tissue. Following the initial implantation trauma, glial tissue formation around the microelectrode and may possibly lead to the microelectrode signal degradation. The aim of this project is to design, develop, and test a compact and power efficient integrated system (IS) that is able to (a) wirelessly transmit triggering signal from the computer to the signal generator which supplies voltage waveforms that move the MEMS microelectrodes, (b) wirelessly transmit neural data from the brain to the external computer, and (c) provide an electrical interface for a closed loop control to continuously move the microelectrode till a proper quality of neural signal is achieved. One of the main challenges of this project is the limited data transmission rate of the commercially available wireless system to transmit 400 kbps of digitized neural signals/electrode, which include spikes, local field potential (LFP), and noise. A commercially available Bluetooth module is only capable to transmit at a total of 115 kbps data transfer rate. The approach to this challenge is to digitize the analog neural signal with a lower accuracy ADC to lower the data rate, so that is reasonable to wirelessly transfer neural data of one channel. In addition, due to the limited space and weight bearing capability to the rodent's head, a compact and power efficient integrated system is needed to reduce the packaged volume and power consumption. 3D SoP technology has been used to stack the PCBs in a 3D form-factor, proper routing designs and techniques are implemented to reduce the electrical routing resistances and the parasitic RC delay. It is expected that this 3D design will reduce the power consumption significantly in comparison to the 2D one. The progress of this project is divided into three different phases, which can be outlined as follow: a) Design, develop, and test Bluetooth wireless system to transmit the triggering signal from the computer to the signal generator. The system is designed for three moveable microelectrodes. b) Design, develop, and test Bluetooth wireless system to wirelessly transmit an amplified (200 gain) neural signal from one single electrode to an external computer. c) Design, develop, and test a closed loop control system that continuously moves a microelectrode in searching of an acceptable quality of neural spikes. The outcome of this project can be used not only for the need of neural application but also for a wider and general applications that requires customized signal generations and wireless data transmission. / Dissertation/Thesis / M.S. Electrical Engineering 2012

L'électrochimie permet la mise en œuvre de techniques de détections pertinentes et adaptées aux contraintes de miniaturisation imposées par la conception de laboratoires sur puce. L'objectif de la thèse a été d'étudier la détection d'espèces électroactives circulant à l'intérieur d'un canal microfluidique, sous la forme de gradients de concentration localisés, ou d'espèces contenues à l'intérieur de gouttes. Pour cela, deux approches ont été menées au moyen d'électrodes microbandes intégrées dans des microcanaux. La première a été d'étudier la possibilité de générer puis de détecter électrochimiquement de façon contrôlée des gradients de concentration en écoulement monophasique. Les réponses ampérométriques ont été analysées en fonction des caractéristiques des gradients de concentration après les phases de génération et de propagation. Deux comportements limites ont été mis en évidence par simulations numériques puis vérifiés expérimentalement. La seconde approche a été de mettre en œuvre une détection électrochimique du contenu de gouttes en écoulement diphasique. L'enjeu a été à la fois de démontrer la faisabilité des mesures mais aussi d'établir des relations entre les courants mesurés et les concentrations ou quantités d'espèces à l'intérieur des gouttes. Dans ce cadre, un microdispositif innovant a été proposé puis testé expérimentalement, démontrant la possibilité d'effectuer des électrolyses totales de gouttes. / Electrochemistry enables the implementation of relevant and appropriate detection techniques to the miniaturization constraints imposed by the design of labs-on-a-chip. The aim of this thesis was to study the detection of electroactive species flowing within microfluidic channels under the form of concentration gradients or microdroplets. Therefore, two approaches were undertaken by means of microband electrodes integrated within microchannels. The first one was to study the opportunity to control the electrochemical generation and detection of concentration gradients in continuous flow. The amperometric responses were analyzed as a function of the characteristics of concentration gradients after the generation and propagation processes. Two boundary behaviours were evidenced by numerical simulations and validated experimentally. The second approach was to implement the electrochemical detection of droplet content in segmented flow. The challenge was both to demonstrate the feasibility of the experiments and to introduce relationships between currents and concentration or amount of species inside droplets. In this context, an innovative microdevice was designed and tested experimentally allowing the total electrolysis of the droplets.

No presente trabalho foi utilizada a microscopia eletroquímica de varredura (SECM) com o objetivo de adquirir informações sobre o processo de corrosão do aço inoxidável 304 em diferentes condições experimentais. Inicialmente, foram realizados ensaios de corrosão com a técnica de voltametria cíclica e acompanhamento do potencial de circuito aberto ao longo do tempo, obtendo-se informações sobre o potencial de circuito aberto e o potencial de pite. Nestes ensaios foram utilizadas soluções de NaCl 0,1 mol L-1 e 0,5 mol L-1 na ausência e presença de O2. Os experimentos com a microscopia eletroquímica de varredura (SECM) foram realizados nas mesmas condições experimentais, em um primeiro momento polarizando o substrato no potencial de circuito aberto específico obtido em cada solução e, em seguida, polarizando-o em 0,5 V (vs Ag/AgCl(KCl sat.)). Trabalhou-se em regiões nas quais havia indícios da formação de pites metaestáveis, monitorando-se o aparecimento de íons Fe(II). Para a realização destes experimentos, o microeletrodo foi polarizado em 0,6V, potencial onde a oxidação de Fe(II) a Fe(III) ocorre em larga extensão. A formação e o rompimento da camada de proteção foram observados de modo generalizado e local. A formação de pite metaestáveis para a solução de NaCl 0,5 mol L-1 também foi notada, sendo esse fato confirmado pela presença de tais pites numa imagem e subsequente desaparecimento na imagem seguinte. / Scanning electrochemical microscopy (SECM) was used in order to acquire information on the corrosion process of stainless steel 304 at different experimental conditions. Corrosion tests were initially carried out with cyclic voltammetry technique and by monitoring the open circuit potential over time to obtain information about the corrosion potential and the pitting potential. Experiments were performed in 0.1 mol L-1 and 0.5 mol L-1 NaCl solutions, in the absence and presence of O2. Scanning electrochemical microscopy (SECM) experiments were performed under the same experimental conditions, by polarizing the substrate at specific open circuit potential of each solution and then polarizing it at 0.5V (vs. Ag / AgCl (KCl sat.)). Experiments were carried out at regions where there were indications of the formation of metastable pits, by monitoring the appearance of Fe(II) ions. The microelectrode was polarized at 0.6V, a potential value where the oxidation of Fe (II) to Fe (III) occurs to a large extent. The formation and the disruption of the protective layer were noticed widely and locally. The formation of metastable pits in 0.5 mol L-1 NaCl solutions was also noted by analysing such pits in an image and their further disappearance in the following image.

A presente tese versa sobre resultados obtidos na aplicação da microscopia eletroquímica de varredura no estudo de sistemas micelares e no estudo de bicamadas lipídicas. Os estudos envolvendo sistemas micelares foram realizados utilizando a SECM no modo substrato-gerador/microeletrodo-coletor. Neste modo de operação, um microeletrodo de platina foi posicionado próximo a um substrato de platina e utilizado para monitorar espécies eletrogeradas nesse substrato. Conhecendo o tempo necessário para a espécie eletrogerada difundir do substrato até o microeletrodo, foi possível aplicar a equação de Einstein-Smoluchowski para determinar o coeficiente de difusão da espécie eletroativa e de micelas de surfactantes. Como as micelas não são eletroativas, o ferroceno eletrogerado no substrato e incorporado nas micelas foi utilizado como sonda para a estimativa do tempo de difusão. Os resultados obtidos para o surfactante brometo de tetradecil trimetil amônio (C14TABr) corroboram dados reportados na literatura, demonstrando a utilidade da metodologia proposta no estudo de sistema micelares. Também foram realizados experimentos envolvendo micelas do surfactante cloreto de 1-alquil-3-metilimidazólio, CxMelmCl (x = 10, 12, 14, 16) e com os resultados obtidos foi possível evidenciar o efeito da cadeia carbônica no coeficiente de difusão das espécies. Os experimentos envolvendo a permeação de substâncias através de bicamadas lipídicas foram realizados em duas etapas. Os primeiros ensaios foram realizados utilizando modelo de membrana semipermeável (papel celofane) com o intuito de verificar a aplicabilidade da SECM no monitoramento de espécies eletroativas que permeiam através da membrana. Na segunda etapa, apresentou-se metodologia para a obtenção de microfuros em folhas de poliestireno utilizados para a formação das bicamadas lipídicas, assim como detalhes sobre a construção da célula de medidas utilizadas nos experimentos de permeação. Foram realizados experimentos envolvendo o uso de bicamadas lipídicas planas obtidas pelo método de Miller preparadas com lecitina de soja. Esses experimentos foram realizados com o intuito de avaliar a estabilidade e para verificar a permeabilidade de algumas substâncias nas bicamadas formadas. Os experimentos de permeação foram realizados posicionando um microeletrodo próximo à membrana, com posterior detecção amperométrica da espécie eletroativa que atravessa a membrana. / This thesis shows results on the use of scanning electrochemical microscopy in the study of micellar systems and lipid bilayers. Studies involving micellar systems were performed by using SECM in the substrate-generator/tip-collector mode. In this operation mode a platinum microelectrode was positioned close to a platinum substrate and used to monitor electrogenerated species on this surface. Taking into account the time for the electrogenerated species to diffuse from the substrate to the microelectrode, the diffusion coefficient of the electroactive species and of the micelles can be calculated by applying the Einstein-Smoluchowski equation. As micelles are not electroactive, ferrocene electrogenerated on the substrate and incorporated into the micelles was used as a probe to estimate the diffusion time. The results obtained for tetradecyl trimethyl ammonium bromide (C14TABr) corroborate those reported in the literature, demonstrating the applicability of the proposed methodology in the study of micellar systems. Experiments with micelles obtained from 1-alkyl-3-methylimidazolium, CxMelmCl (x = 10, 12, 14, 16) chloride surfactants were also performed and results showed the effect of the carbon chain in the diffusion coefficient. Experiments involving the permeation of chemical species through lipid bilayers were carried out in two steps. A membrane model (cellophane) was preliminary used in order to investigate the possibility of using SECM as a tool for monitoring the permeation of electroactive species through the membrane. Then, a methodology for obtaining microholes in polystyrene sheets used to form lipid bilayers was presented, as well as details about the design of an electrochemical cell used in the permeation experiments. Experiments involving the use of planar lipid bilayers obtained by the method of Miller prepared using soybean lecithin were performed. These experiments were carried out in order to evaluate the stability and to check the permeation of some substances through the prepared bilayers. Permeation experiments were performed by placing the microelectrode close to the membrane with subsequent amperometric detection of any electroactive species that cross the membrane

A determinação dos íons Cd(II) e Zn(II) foi realizada em amostras de águas estuarinas por voltametria de redissolução anódica utilizando microeletrodo de fibra de carbono (raio =3 &#181;m). O filme de bismuto foi depositado in situ, simultaneamente com os analitos em microeletrodo sob as condições otimizadas. O intervalo linear da curva de calibração para ambos os íons metálicos foi 0,5 -10,0 nmol L-1 e os limites de detecção de Cd(II) e Zn(II) foram estimados em 17 e 52 pmol L-1, respectivamente. A precisão dos resultados fornecidos empregando-se o microeletrodo de filme de bismuto (BiFME) foi avaliada pela realização de experimento com uma amostra certificada e teste de recuperação. A utilidade da metodologia foi demonstrada aplicando o BiFME para determinar baixas concentrações de Cd(II) e de Zn(II) em água do estuário. / A bismuth-film electrode for use in anodic stripping voltammetry was employed in order to quantify Cd(II) and Zn(II) in estuarine water samples. The bismuth film was deposited in situ simultaneously with the analytes onto a carbon fiber disc microelectrode (radius = 3 &#181;m). Under the optimised conditions, calibration plots for both metallic ions were obtained in the range 0.5 to 10.0 nmol L-1 and the limits of detection for Cd(II) and Zn(II) were estimated as 17 and 52 pmol L-1, respectively. The accuracy of the results supplied by the bismuth film microelectrode (BiFME) was assessed by performing experiment with a certified sample and addition-recovery experiments. The usefulness of the methodology was demonstrated by applying the BiFME to measuring the Cd(II) and Zn(II) content in estuarine water.