The high surface to volume ratio which is a property of nanoscale devices means the interfacial effects from these devices on the mass transport of analyte can be significant. Quartz nanopipette effect on the mass transport behavior of inorganic monovalent salts such as potassium chloride is shown to differ from those of conical nanopore. Quartz nanopipettes demonstrate a more significant interfacial impact on the mass transport behavior of inorganic salts. This is evidenced by significant impacts on ionic transport even at high electrolyte concentration where nanopore interfacial effects do not significantly impact the ion transport. Nanopipettes have been use to precipitate salts such as lithium chloride in bulk concentrations three orders of magnitude below the saturation concentration. These novel interfacial interactions have opened new avenues for crystallization of more complex organic biomolecules using inorganic systems as model systems on which to base the approach for these more complex systems.

Ultramicroelectrodes (UMEs) (limiting dimensions <~25 μm) and nanoelectrodes (<~100 nm) exhibit enhanced electrochemical properties compared to macroscopic electrodes. Their small sizes and enhanced properties make them well-suited for various interesting and important applications such as measuring redox-active species in nonaqueous solvents, studying intermediates of fast electrochemical reactions, and investigating electrochemical and electrocatalytic properties of single nanoparticles. While UMEs are commercially available, nanoelectrode fabrication is still largely confined to research labs. Various methods for constructing nanoelectrodes have been reported and continue to be developed, but most require considerable expertise, and comparisons between different fabrication processes are lacking. In this work, a comparison of laser-assisted pulling and chemical vapor deposition (CVD) methods of electrode fabrication is made with the aim of optimizing production of carbon nanoelectrodes for single nanoparticle electrochemical measurements. By examining effects of pulling parameters, post-pulling treatments, and CVD processing, electrodes as small as ~50 nm were successfully produced.

The ‘missing wedge’ is a long-standing problem in electron tomography, caused by the use of slab-like flat specimens, which increase in thickness when tilted to high angles. Attempts have been made to reduce the undesirable effects caused by the missing wedge, but the problem remains, particularly for the radiation-sensitive frozen-hydrated specimens used for high resolution imaging. Specimens with cylindrical symmetry offer a way to overcome this problem, since the thickness remains constant at all viewing angles. However, while this has been suggested before, it has never been demonstrated for frozen-hydrated specimens. In this work, I present a way to make cylindrical specimens for electron cryo-tomography, using thin-walled carbon tubes as specimen holders. The tubes are made in a multi-step process, involving carbon deposition on glass micropipette templates and subsequent removal of the glass. Tube diameters are typically a few hundred nanometres, with a wall thickness of 10–20 nm. To make frozen-hydrated specimens, the tubes are filled with an aqueous sample and then plunge-frozen in liquid ethane. Electron images acquired from the tubes have equal quality at all viewing angles, with a tilt range restricted only by the physical limits of the microscope. Tomograms from specimens such as gold particles and liposomes show that the effects of the missing wedge are substantially reduced, with much improved resolution along the electron beam axis. Structural features oriented in all directions are visible in the reconstructions, in marked contrast to tomograms acquired over a more restricted angular range. These results are promising, however some technical challenges remain before this method can be used routinely.

No description available.

The ability to precisely count inorganic and organic nanoparticles and to measure their size distribution plays a major role in various applications such as drug delivery, nanoparticles counting, and many others. In this work I present a simple resistive pulse method that allows translocations, counting, and measuring the size and velocity distribution of silica nanoparticles and liposomes with diameters from 50 nm to 250 nm. This technique is based on the Coulter counter technique, but has nanometer size pores. It was found that ionic current drops when nanoparticles enter the nanopore of a pulled micropipette, producing a clear translocation signal. Pulled borosilicate micropipettes with opening 50 ~ 350 nm were used as the detecting instrument. This method provides a direct, fast and cost-effective way to characterize inorganic and organic nanoparticles in a solution. In this work I also introduce a newly developed Capillary Ionic Transistor (CIT). It is presented as a nanodevice which provides control of ionic transport through nanochannel by gate voltage. CIT is Ionic transistor, which employs pulled capillary as nanochannel with a tip diameter smaller than 100 mm. We observed that the gate voltage applied to gate electrode, deposited on the outer wall of a capillary, affect a conductance of nanochannel, due to change of surface charge at the solution/capillary interface. Negative gate voltage corresponds to lower conductivity and positive gate increases conductance of the channel. This effect strongly depends on the size of the channel. In general, at least one dimension of the channel has to be small enough for electrical double layer to overlap.

Esta tese apresenta os achados e avanços obtidos na fabricação, caracterização e aplicação de pontas de prova eletroquímicas multifuncionais para a obtenção de informações eletroquímicas resolvidas no espaço em diversas superfícies/interfaces por meio de técnicas de microscopia de varredura de ponta de prova eletroquímica (SEPM, em inglês). Diferentes designs de pontas de prova multifuncionais foram investigados e, devido a natureza não convencional destas, novos métodos para fabricação e caracterização foram desenvolvidos. Os benefícios da utilização de pontas de prova multifuncionais para a obtenção de informações eletroquímicas resolvidas no espaço ficaram evidente durante a realização de experimentos \"prova de conceito\", onde a maior densidade de informação obtida permitiu o estudo de sistemas mais complexos e a aquisição de informações eletroquímicas livre de interferência topográfica mesmo em superfícies não planas. A hibridização de diferentes técnicas de microscopia de varredura de ponta de prova eletroquímica em uma única ponta de prova também foi investigada o que se provou extremamente útil para a aquisição de imagens eletroquímicas de alta resolução, livres de influências topográficas, quando utilizada a técnica de microscopia de condutividade iônica (SICM, em inglês) como sensor de topografia do substrato investigado. Por ultimo, uma nova técnica, baseada na microscopia de condutividade iônica, que se utiliza de pontas de prova eletroquímicas multifuncionais fabricadas a partir de uma nanopipeta de um único canal, foi desenvolvida. Esta nova técnica se mostrou extremamente ponderosa, capaz de obter informações a respeito da topografia e mapear sítios ativos sobre um substrato utilizando uma nanopipeta de um único canal com alta resolução especial e temporal a uma taxa de aproximadamente 4000 pixels por Segundo. / This thesis presents the findings and advances made on fabrication, characterization and application of multifunctional electrochemical probes to acquire space resolved electrochemical information on diverse surfaces/interfaces employing Scanning Electrochemical Probe Microscopy (SEPM) techniques. Different multifunctional probes designs were investigated and new and innovative methods for fabrication and characterization of those probes were developed, which was necessary due to the unconventional nature of most of the probes studied. The benefits of using multifunctional probes for space resolved electrochemical measurements was clear during \"proof-of-concept\" experiments, where the increased density of information allowed the study of complex systems and the acquisition of topography-free electrochemical information of rough surfaces. The hybridization of different SEPM techniques in a single probe tip was also investigated, and this was found to be extremely beneficial, especially for acquiring high-resolution, topography-free, electrochemical images employing Scanning Ion Conductance Microscopy as a topography feedback. Finally, a new SICM technique, based on the use of a multifunctional probe tip fabricated from a single barrel nanopipette, was developed. This new technique was found to be extremely powerful, capable of acquiring information on topography and map active sites over substrates using a single barrel pipette with high spatial and temporal resolution at a rate of approx. 4000 pixels per second.

Esta tese apresenta os achados e avanços obtidos na fabricação, caracterização e aplicação de pontas de prova eletroquímicas multifuncionais para a obtenção de informações eletroquímicas resolvidas no espaço em diversas superfícies/interfaces por meio de técnicas de microscopia de varredura de ponta de prova eletroquímica (SEPM, em inglês). Diferentes designs de pontas de prova multifuncionais foram investigados e, devido a natureza não convencional destas, novos métodos para fabricação e caracterização foram desenvolvidos. Os benefícios da utilização de pontas de prova multifuncionais para a obtenção de informações eletroquímicas resolvidas no espaço ficaram evidente durante a realização de experimentos \"prova de conceito\", onde a maior densidade de informação obtida permitiu o estudo de sistemas mais complexos e a aquisição de informações eletroquímicas livre de interferência topográfica mesmo em superfícies não planas. A hibridização de diferentes técnicas de microscopia de varredura de ponta de prova eletroquímica em uma única ponta de prova também foi investigada o que se provou extremamente útil para a aquisição de imagens eletroquímicas de alta resolução, livres de influências topográficas, quando utilizada a técnica de microscopia de condutividade iônica (SICM, em inglês) como sensor de topografia do substrato investigado. Por ultimo, uma nova técnica, baseada na microscopia de condutividade iônica, que se utiliza de pontas de prova eletroquímicas multifuncionais fabricadas a partir de uma nanopipeta de um único canal, foi desenvolvida. Esta nova técnica se mostrou extremamente ponderosa, capaz de obter informações a respeito da topografia e mapear sítios ativos sobre um substrato utilizando uma nanopipeta de um único canal com alta resolução especial e temporal a uma taxa de aproximadamente 4000 pixels por Segundo. / This thesis presents the findings and advances made on fabrication, characterization and application of multifunctional electrochemical probes to acquire space resolved electrochemical information on diverse surfaces/interfaces employing Scanning Electrochemical Probe Microscopy (SEPM) techniques. Different multifunctional probes designs were investigated and new and innovative methods for fabrication and characterization of those probes were developed, which was necessary due to the unconventional nature of most of the probes studied. The benefits of using multifunctional probes for space resolved electrochemical measurements was clear during \"proof-of-concept\" experiments, where the increased density of information allowed the study of complex systems and the acquisition of topography-free electrochemical information of rough surfaces. The hybridization of different SEPM techniques in a single probe tip was also investigated, and this was found to be extremely beneficial, especially for acquiring high-resolution, topography-free, electrochemical images employing Scanning Ion Conductance Microscopy as a topography feedback. Finally, a new SICM technique, based on the use of a multifunctional probe tip fabricated from a single barrel nanopipette, was developed. This new technique was found to be extremely powerful, capable of acquiring information on topography and map active sites over substrates using a single barrel pipette with high spatial and temporal resolution at a rate of approx. 4000 pixels per second.

Most biological experiments are performed on an ensemble of cells under the assumption that all cells are identical. However, recent evidence from single cells studies reveals that this assumption is incorrect. Individual cells within the same generation may differ dramatically, and these differences have important consequences for the health and function of the entire living body. I have used Scanning Ion Conductance Microscopy (SICM) for imaging and analysis of topographical change of single cell membrane, which is difficult to be revealed by optical microscopes. Morphological change in the fixed and live HeLa cell membrane during endocytosis of conjugated polymer nanoparticles was studied. Results demonstrated SICM is a powerful tool to study the interaction between nanoparticle and cell membrane during internalization of nanoparticles through the membrane. This research can improve our fundamental understanding of cellular behavior and will be helpful for drug delivery applications. Based on conventional SICM, we have developed a novel method to simultaneous map the topography and potential distributions of the single living cells membranes. At the first step, multifunctional nanopipettes (nanopore/nanoelectrode) have been fabricated and characterized. To demonstrate the potential sensing capability and understand the mechanism, I measured the ionic current and local electric potential change during translocation of 40 nm charged gold nanoparticles. Our results reveal the capability of the multifunctional probe for the highly sensitive detection of the ionic current and local electrical potential changes during the translocation of the charged entity through the nanopore. From the potential change, we revealed the dynamic assembly of GNPs before entering the nanopore. The experimental results are also nicely explained by the finite element method based numerical simulation results. At the second step, I have measured the surface potential of living cell membrane at selected locations. Very recently, I have obtained results to show that we can map the extracellular membrane potential distribution of the complicated living cell membrane with sub-micron spatial resolution.This new imaging technique can help biologist to explore the extracellular potential distribution of varieties of cells quantitatively.These studies will have impacts on several biomedical applications such as regenerative repair and cancer treatment.