Intracellular delivery of macromolecules is crucial for the success of many research and clinical applications. Several conventional intracellular delivery methods have been used for many years but are still inadequate for several applications because of the issues associated with toxicity, low-throughput, and/or difficulty to target certain cell types. In this study, we developed and evaluated new high-throughput intracellular delivery methods for the efficient delivery of macromolecules while maintaining high cell viability. First, we studied the feasibility of using an array of nanoneedles, with sharp tip diameters in the range of tens of nanometers, to physically make transient holes in cell membranes for intracellular delivery. Puncture loading and centrifuge loading methods were developed and assessed for the effect of various experimental parameters on cell viability and delivery efficiency of fluorescent molecules. In both methods, high-throughput intracellular delivery was feasible by creating transient holes in cell membranes with the sharp tips of the nanoneedles. The second physical intracellular delivery method we studied was a novel microfluidic device that created transient holes in the cell membrane by mechanical deformation and shear stress to the cell. We observed efficient delivery of fluorescent molecules and studied the effect of device design and flow pressure on the delivery efficiency compared to data in the literature. We accounted for cell loss and clogging in the microfluidic devices and determined the true loss of cell viability associated with this method. Lastly, we investigated the possibility of intracellular delivery using nanoparticles on a leukemia cell line. Among number of materials for nanoparticles tested, mesoporous silica/poly-L-lysine nanoparticles were selected for further intracellular delivery study based on cell viability and intracellular delivery capability. We demonstrated the co-delivery of protein and plasmid by encapsulating into and coating onto the surface of the nanoparticles, respectively, which would be advantageous for certain therapeutic strategies. In summary, this work introduced two new intracellular delivery methods involving nanoneedles and novel nanoparticles, and provided an early, independent assessment of microfluidic delivery, showing the strengths and weaknesses of each method. These methods can be further optimized for a number of laboratory and clinical applications with continued research.

The rational and directed delivery of genetic material to the cell is a formidable tool to investigate the phenotypic effects of gene expression regulation and a promising therapeutic strategy for genetic defects. RNA interference constitutes a versatile approach to gene silencing. Despite the development of numerous strategies the transfection of small interfering RNA (siRNA) is highly dependent on cell type and conditions. Direct physical access to the intracellular compartment is a promising path for high efficiency delivery independently of cell type and conditions. Silicon nanowires grant such access with minimal toxic effects, and allow intracellular delivery of DNA when actuated by atomic force microscope. These findings reveal the potential for porous silicon nanostructures to serve as delivery vectors for nucleic acids due to their porous nature, elevated biocompatibility, and biodegradability. This dissertation illustrates the development a novel platform for efficient siRNA transfection based on an array of porous silicon nanoneedles. The synthesis of biodegradable and biocompatible porous nanowires was accomplished by a novel strategy for electroless etch of silicon that allows anisotropic etch simultaneously with porosification. An ordered array of cone shaped porous silicon nanoneedles with tunable tip size, array density and aspect ratio was obtained coupling this strategy with patterned metal deposition and selective reactive ion etch. This process also granted control over porosity, nanopore size and flexural modulus. The combination of these parameters was appropriately optimized to ensure cell penetration, maximize siRNA loading and minimize cytotoxic effects. Loading of the negatively charged siRNA molecules was optimized by applying an external electric field to the nanoneedles under appropriate voltage conditions to obtain a tenfold increase over open circuit loading, and efficient penetration of the siRNA within the porous volume of the needles. Alternative surface chemistry modification provided a means for effective siRNA loading and sustained release. siRNA transfection was achieved by either imprinting the nanoneedles array chip over a culture of MDA-MB-231 cells or allowing the cells to self-impale over the needles. The procedures allowed the needles to penetrate across the cell membrane without influencing cell proliferation. siRNA was successfully transfected and was effective at suppressing gene expression. / text

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Wir haben blau, grün und orange leuchtende organische Nanofäden oder Nanonadeln und Mikroringe aus para-Hexaphenyl (p-6P), alpha-Quaterthiophen (alpha-4T) und alpha-Sexithiophen (alpha-6T) mittels Organischer Molekularstrahlepitaxie (OMBE) auf Muskovit Glimmer hergestellt. Die Aggregate haben wir mit der Atomkraftmikroskopie, mit der Fluoreszenz-Mikroskopie und durch UV-vis Spektroskopie charakterisiert. Auf der Muskovit Oberfläche wachsen p-6P Fäden parallel zueinander auf und zeigen zwei verschiedene Orientierungsdomänen entlang [110] und [1-10]. Mit Hilfe einer systematischen statistischen Analyse diskutieren wir das Wachstum dieser p-6P Nadeln für verschiedene Wachstumsbedingungen. Zusätzlich zu den Fäden haben wir p-6P Cluster auf der Oberfläche beobachtet. Nadeln werden durch die Aggregation solcher Cluster gebildet. Ein Realraummodell der Morphologie der Nadeln sowie ein Modell für deren Wachstum werden vorgestellt. Indem wir Glimmer zunächst mit einer dünnen Goldschicht bedecken und die Wachstumsparameter variieren, erreichen wir eine weitgehende Kontrolle der Morphologie der Nadeln (Länge von 0,5 Mikrometer bis 1 mm, Höhe von 25 bis 300 nm und Breite von 100 bis 600 nm). Im Gegensatz zu p-6P orientieren Thiophene ihre Wachstumsrichtungen an allen hoch symmetrischen Richtungen von Glimmer. Es wird gezeigt, dass die Mechanismen für das Fadenwachstum von beiden Oligomere gleich sind, nämlich eine Kombination aus Epitaxie und einer Dipol-unterstützten Ausrichtung. Auch die Strukturen dieser Fäden sind ähnlich: die Moleküle liegen parallel angeordnet auf der Oberfläche, ihre Längsachsen orientieren sich schräg zur Längsachse der Fäden. Auf mit Wasser oder Methanol vorbehandeltem Glimmer wachsen diese beiden Oligomere als gebogene Fäden und Mikroringe auf. Diese Oberflächenvorbehandlungen sowie das Wachstum von p-6P auf Gold/Glimmer unterstützen auch den Wachstumsmechanismus auf der sauberen Glimmer-Oberfläche. / By using organic molecular beam epitaxy (OMBE) blue, green and orange light emitting organic nanofibers or nanoneedles and microrings from para-hexaphenyl (p-6P), alpha-quaterthiophene (alpha-4T) and alpha-sexithiophene (alpha-6T), respectively, on muscovite mica surfaces are generated. The aggregates are characterized by atomic force microscopy, fluorescence microscopy and UV-vis spectroscopy. On muscovite mica, p-6P fibers usually grow mutually parallel showing two domains of their orientations with an angle of 120 degree in between. The detail growth of nanofibers from p-6P by performing a systematic statistical analysis of fibers as a function of various growth conditions is discussed. Furthermore, the morphology exhibits p-6P clusters, which are found to be fibers´ building blocks. A real space model of the fiber and a model for their growth are also presented. By introducing a thin gold layer on mica prior to p-6P deposition together with varying growth parameters, the morphology of fibers is controlled in a wide range (length from 0.5 micrometer to 1 mm, height from 25 to 300 nm and width from 100 to 600 nm). In contrast to p-6P, thiophene fibers exhibit various orientations close to mica high symmetry directions. It is shown that the mechanism behind the fiber growth from all molecules on mica is the same, i.e. a combination of epitaxy and dipole assisted growth process. The fiber microscopic structures are similar, too: molecules take lying orientations and they hold themselves parallel pointing their long axes along an oblique direction off the long fiber axis. The growth of both types of oligomers on water or methanol treated mica surfaces leads to the formation of bent fibers and microrings. This surface pretreatment and the growth of p-6P on gold/mica support the fiber growth mechanism on plain mica.

Zinc oxide (ZnO) is perhaps one of the most widely studied material in the last two decades. It has received so much of attention because of its incredible potential for wide ranging applications. ZnO is a wide band gap semiconductor (Eg = 3.37 eV at 300 K) with a rather large excitonic binding energy (~60 meV). This combination of properties makes it an ideal choice for several optoelectronic devices that can easily work at room temperature. ZnO is a truly multifunctional material possessing several desirable electrical, optical, optoelectronic, and piezoelectric properties. In addition, it is highly amenable to production of various kinds of nanostructures such as nanorods, nanotubes, nanoribbons, nanoneedles, etc., which makes it even more desirable for nanoscale devices. Examples of ZnO based nanodevices could include photodiodes, photodetectors, nano-lasers, field-emission devices and memristors. In order to make such devices, one could need device quality nanostructures that must be reproducible and cost effective. Naturally, one has to look for a synthesis process that has great controls and is relatively inexpensive. The study provided here shows that among the various methods available for ZnO synthesis, the microwave-assisted chemical synthesis offers outstanding advantages in terms of rapid growth of nanostructures, economical use of energy and excellent controls of process parameters. In order to produce device quality ZnO nanostructures using microwave-assisted synthesis, one has to study the effect of various process parameters and optimise them for the desired growth. Therefore, in the current study, first, a systematic study was undertaken to synthesize ZnO nanostructures both in a aqueous and non-aqueous medium and their characterization was carried out in order to understand the effect of microwave power, time of irradiation, pressure, solvent and salt concentration, etc. The goal was to develop synthesis protocols for various kinds of nanostructures that could guarantee reproducibility, good yield, and device quality structures. This study has led to successful growth of ZnO nanostructures on various substrates, vertically aligned ZnO nanorods and templated arrays of desired structures, all with outstanding properties of the structures as confirmed by XRD, MicroRaman, photoluminescence, cathodoluminescence, FESEM, TEM, PFM studies and pole figure analysis. Piezoelectric force microscopy (PFM) and physical property measurement system (PPMS, Quantum Design), have been used to study the multifunctional properties of ZnO nanostructures. The PFM is a powerful technique to measure the local piezoelectric coefficient of nanostructures and nanoscale thin films. PFM works on the converse piezoelectric effect in which electric potential is applied and mechanical strain is measured using a cantilever deflection. The PFM (Brucker’s AFM dimension Scan Assist) was used to characterize individual ZnO nanorods. Extensive studies were carried out with PFM measurements and it was observed that the nanorods consistently showed high piezoelectric coupling coefficients (d33~50-154 pm/V). It was also found that the variation in d33 depended on morphology and size of nanostructure. The multifunctional properties were observed in small ZnO nanocrystals (NCs). Such high values of piezoelectric coupling coefficients open the door for novel ZnO based nanoscale sensors and actuators. The synthesized ZnO nanostructures were further optimized and characterized keeping in view three device applications namely Field emission, Memristors and Gas Sensors. The fabrication and characterization of these three devices with ZnO nanostructure was carried out using electron beam lithography and direct laser writing micromachining. Device fabrication using lithography involved several steps such as substrate cleaning, photoresist spin coating, pre-baking, post-baking, pattern writing, developing, sputtering/deposition of material for lift-off, ZnO growth, and overlay lithography. For field emission devices, high quality, well aligned, c-axis oriented ZnO nano-needles were grown on sputter coated Ti/Pt (20nm/100nm) on SiO2/Si substrate by rapid microwave-assisted method in aqueous medium. The diameter of the tip was found to be 1~2 nm and the length of the rod was approximately 3~5μm. For a particular batch the tip size, morphology, and lengths were found to be the same and highly repeatable. Pole figure analysis revealed that nanorods were highly oriented towards <002> direction. Field-emission measurements using the ZnO nanoneedles arrays as cathode showed very low turn-on electric field of 0.9 V/μm and a very high field enhancement factor ~ 20200. Such a high emission current density, low turn-on electric field, and high field enhancement factor are attributed to the high aspect ratio, narrow tip size, high quality and single crystallinity of the nanoneedles. The high emission current density, high stability, low threshold electric field (0.95 V/μm) and low turn-on field make the ZnO nanoneedle arrays one of the ideal candidates for field-emission displays and field emission sensors. In the suitability of ZnO nanostructures for memristor application it was found that the single crystalline ZnO nanorods were not suitable as they did not show memristive behaviour but the ZnO nanorods with native defects exhibited considerable memristive behaviour. Therefore the microwave-assisted grown ZnO nanorods with defects were used to fabricate memristive devices. Single and multiple ZnO nanorods based memristors were fabricated using electron beam lithography. These devices were characterized electrically by measuring the hysteresis in the I/V characteristics. A high degree of repeatability has been established in terms of growth, device fabrication, and measurements. The switching in single nanorod based devices was found to have “ON-to- OFF” resistance ratio of approximately 104 and current switching ratio (ION/IOFF) of 106. Gas sensing based on electrical resistance change depends on absorption and desorption rate of gases on the analyte which is governed by surface properties, morphologies and activation energy. Therefore, various morphologies of nanostructure were grown for gas sensing application. Through experimentation, the emphasis shifted to c-axis oriented ZnO nanostructures on SiO2 substrate for gas sensing. The c-axis orientation of ZnO nanostructures was preferred mainly due to its huge surface area. The measurements showed that the c-axis oriented ZnO nanorods were excellent hydrogen sensors, able to detect H2 as low concentration as 2 ppm, even when the sensing temperature is as low as 200 ˚C. However, oxygen sensing was achieved at a higher temperature (300 ˚C). Thus, the study undertaken in this thesis presents a microwave based rapid and economical method for synthesizing high quality, device grade ZnO nanostructures, their extensive characterization that shows the multifunctional properties of these structures, and there examples of varied device applications of the synthesized nanostructures as field emitters, memristors, and gas sensors.

In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer. In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates. (i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.