Yes / The adsorption of three homo-tripeptides, HHH, YYY, and SSS, at the aqueous Au interface is investigated, using molecular dynamics simulations. We find that consideration of surface facet effects, relevant to experimental conditions, opens up new questions regarding interpretations of current experimental findings. Our well-tempered metadynamics simulations predict the rank ordering of the tripeptide binding affinities at aqueous Au(111) to be YYY > HHH > SSS. This ranking differs with that obtained from existing experimental data which used surface-immobilized Au nanoparticles as the target substrate. The influence of Au facet on these experimental findings is then considered, via our binding strength predictions of the relevant amino acids at aqueous Au(111) and Au(100)(1 × 1). The Au(111) interface supports an amino acid ranking of Tyr > HisA ≃ HisH > Ser, matching that of the tripeptides on Au(111), while the ranking on Au(100) is HisA > Ser ≃ Tyr ≃ HisH, with only HisA showing non-negligible binding. The substantial reduction in Tyr amino acid affinity for Au(100) vs Au(111) offers one possible explanation for the experimentally observed weaker adsorption of YYY on the nanoparticle-immobilized substrate compared with HHH. In a separate set of simulations, we predict the structures of the adsorbed tripeptides at the two aqueous Au facets, revealing facet-dependent differences in the adsorbed conformations. Our findings suggest that Au facet effects, where relevant, may influence the adsorption structures and energetics of biomolecules, highlighting the possible influence of the structural model used to interpret experimental binding data. / Air Office of Scientific Research, Grant No. FA9550-12-1-0226

No description available.

The emerging field of RNA nanotechnology necessitates creation of functional RNA nanoparticles, but has been limited by particle instability. Previously, it was found the three-way junction (3WJ) of the Phi29 DNA packaging motor pRNA was found to be ultra-stable and assemble in solution without the presence of metal ions. The three-way junction is composed of three short oligo RNA strands and proven to be thermodynamically stable. Here the assembly mechanism, thermodynamic and enzymatic stabilities, and kinetics are examined in order to understand the stability behind this unique motif. Thermodynamic and kinetics studies found that the pRNA 3WJ formed out of three components at a rapid rate creating a single-step three component collision with a lack of dimer intermediate formation while being governed by entropy, instead of the commonly seen enthalpy. Furthermore, the pRNA 3WJ proved to be stable at temperatures above 50 °C, concentrations below 100 pM, and produced a free energy of formation well below other studied RNA structures and motifs. With the high stability and folding efficiency of the pRNA 3WJ, it serves as an ideal platform for multi-branched RNA nanoparticles constructed through bottom-up techniques. RNA nanoparticles were constructed for the specific targeting of prostate cancer cells expressing Prostate Specific Membrane Antigen (PSMA) by receptor mediated endocytosis through the addition of an RNA aptamer; and the delivery of anti-miRNA sequences for gene regulation. The resulting nanoparticles remained stable while showing highly specific binding and entry in PSMA positive cells through cell surface receptor endocytosis. Furthermore, the entry of the nanoparticles allowed for the knockdown of against onco-miRNAs. Nanoparticles harboring antimiRNAs led to the upregulation of tumor suppressor genes, and signaling of apoptotic pathways. These findings display RNA nanotechnology can result in the production of stable nanoparticles and result in the specific treatment of cancers, specifically prostate cancer.

This work presents a new low-temperature fabrication process of metal oxide nanostructures that allows high-aspect ratio zinc oxide (ZnO) and titanium dioxide (TiO2) nanowires and nanotubes to be readily integrated with microelectronic devices for sensor applications. This process relies on a new method of forming a close-packed array of self-assembled high-aspect-ratio nanopores in an anodized aluminum oxide (AAO) template in a thin (2.5 µm) aluminum film deposited on a silicon and lithium niobate substrate (LiNbO3). This technique is in sharp contrast to traditional free-standing thick film methods and the use of an integrated thin aluminum film greatly enhances the utility of such methods. We have demonstrated the method by integrating ZnO nanowires, TiO2 nanowires, and multiwall TiO2 nanotubes onto the metal gate of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and the delay line of a surface acoustic wave (SAW) device to form an integrated ChemFET (Chemical Field-Effect Transistor) and a orthogonal frequency coded (OFC) SAW gas sensor. The resulting metal oxide nanostructures of 1-1.7 µm in height and 40-100 nm in diameter offer an increase of up to 220X the surface area over a standard flat metal oxide film for sensing applications. The metal oxide nanostructures were characterized by SEM, EDX, TEM and Hall measurements to verify stoichiometry, crystal structure and electrical properties. Additionally, the electrical response of ChemFETs and OFC SAW gas sensors with ZnO nanowires, TiO2 nanowires, and multiwall TiO2 nanotubes were measured using 5-200 ppm ammonia as a target gas at room temperature (24ºC) showing high sensitivity and reproducible testing results.

The ability to control the bi-stable magnetization states of shape anisotropic single domain nanomagnets has enormous potential for spawning non-volatile and energy-efficient computing and signal processing systems. One of the most energy efficient switching methods is to adopt a system of a 2-phase multiferroic nanomagnet, where a voltage applied on the piezoelectric layer generates a strain in it and the strain is elastically transferred to the magnetostrictive nanomagnet which rotates the magnetization states of the nanomagnet at room temperature via the converse magnet-electric effect. Recently, it has been demonstrated that the magnetization of a Co nanomagnet can be switched between two stable orientations by this technique. The switching probability, however, is low due to the relatively small magnetostriction of Co. One possible way to improve the statistics is to use a better magnetostrictive material like Galfenol which has much higher magnetostriction and is therefore desirable, but it also presents unique material challenges owing to the existence of many phases. Nonetheless, there is a need to step beyond elemental ferromagnets and examine compound or alloyed ferromagnets with much higher magnetostriction to advance this field. There has not been much work in nanoscale FeGa magnets which are important for nanomagnetic logic and memory applications. Here, we have experimentally demonstrated switching of magnetization of Galfenol nanomagnets and proposed a core component of ultra-energy-efficient memory cell. We also demonstrated a bit writing scheme which completely reverses the magnetization with only strain, thus overcoming the fundamental obstacle of strain induced switching of magnetizations of nanomagnets.

The rational design, synthesis, and characterization of several systems that undergo self-assembly are described. Systems were chosen based on their ability to self-assemble in a highly ordered and predictable fashion that imparts order on the structure such that it is able to perform a given device function. Herein we describe self-assembled multilayered thin films on gold that can behave as molecular wires with tunable length, photocurrent generating films, and surfaces with photoswitchable wettability, and self-assembling peptide nanotubes that can potentially function as long range energy and electron transfer conduits. A non-covalent, modular approach to multilayered thin film fabrication was used to generate three thin film systems that function as molecular scale wires, photocurrent generating devices, and photoswitchable thin films, respectively. These films were based on 4-[(10-mercaptodecyl)oxy]pyridine-2,6-dicarboxylic acid self-assembled monolayers on gold. These monolayers are able to chelate metal (II) ions, and thus multilayers were assembled based on metal-ligand coordination chemistry. The three systems described were characterized by contact angle measurements, electrochemical methods, and grazing angle IR spectroscopy. All three systems emphasize the versatility of a modular approach to thin film construction, and provide proof-of-concept for future studies. A cyclic octapeptide architecture was employed as a scaffold for the predictable self-assembly of photoactive groups within a nanotubular structure. The degree of cyclic peptide aggregation in stacking nanotube systems and non-stacking monomer systems, was studied via fluorescence emission spectroscopy. Based on the spectral results, it was determined that peptide nanotubes can be constructed such that photoactive side chains can be assembled in stacks. Future experiments for the determination of long range energy and/or charge transfer in these systems are also discussed.

Ng, Yiu Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 99-114). / Abstracts in English and Chinese. / Acknowledgements --- p.2 / Abstract --- p.3 / 摘要 --- p.5 / Content --- p.6 / List of abbreviations and symbols --- p.10 / Chapter Chapter 1 - --- Introduction --- p.13 / Chapter 1.1 --- Introduction to nanoparticles (NPs) --- p.13 / Chapter 1.2 --- How to treat solid cancers using nanoparticle drugs --- p.17 / Chapter 1.3 --- What is Chitosan (CS)? --- p.22 / Chapter 1.4 --- Possible peptide candidates to be trapped --- p.26 / Chapter 1.4.1 --- Luffin PI - Ribosome inactivating peptide --- p.26 / Chapter 1.4.2 --- Buforin lib (Bllb) - Antimicrobial peptide --- p.27 / Chapter 1.5 --- Aims of study --- p.30 / Chapter Chapter 2 - --- Materials and Methods --- p.31 / Chapter 2.1 --- Materials --- p.31 / Chapter 2.2 --- Methods --- p.31 / Chapter 2.2.1 --- Construction and expression of Luffin P1 --- p.31 / Chapter 2.2.2 --- Circular dichroism spectroscopy --- p.32 / Chapter 2.2.3 --- Static light scattering --- p.33 / Chapter 2.2.4 --- In vitro N-glycosidase assay --- p.34 / Chapter 2.2.5 --- Preparation of CS particles --- p.34 / Chapter 2.2.5.1 --- Preparation of positive CS NPs --- p.34 / Chapter 2.2.5.2 --- Preparation of negative CS NPs --- p.35 / Chapter 2.2.5.3 --- Preparation of buforin lib incorporated NPs --- p.35 / Chapter 2.2.5.4 --- Preparation of Cy5 incorporated NPs --- p.36 / Chapter 2.2.6 --- Characterization of CS NPs --- p.36 / Chapter 2.2.7 --- Buforin lib (Bllb) encapsulation efficiency and loading capacity --- p.36 / Chapter 2.2.8 --- In vitro release study --- p.37 / Chapter 2.2.9 --- Confocal Microscopy --- p.37 / Chapter 2.2.10 --- Cytotoxicity assay --- p.38 / Chapter 2.2.11 --- Statistical analysis --- p.38 / Chapter Chapter 3 - --- "Cloning, expression, purification and structural characterization of Luffin PI" --- p.39 / Chapter 3.1 --- Introduction --- p.39 / Chapter 3.2 --- Results --- p.41 / Chapter 3.2.1 --- Construction of Luffin PI plasmid --- p.41 / Chapter 3.2.2 --- Expression and purification of Luffin PI --- p.41 / Chapter 3.3.3 --- Molecular weight and secondary structure determination of Luffin PI --- p.43 / Chapter 3.3.4 --- 3D solution structure of Luffin PI --- p.45 / Chapter 3.3.5 --- In vitro N-glycosidase activity of Luffin PI --- p.49 / Chapter 3.3 --- Discussion --- p.51 / Chapter Chapter 4 - --- Generation of positively charged CS particles and Bllb incorporation --- p.60 / Chapter 4.1 --- Introduction --- p.60 / Chapter 4.2 --- Results --- p.62 / Chapter 4.2.1 --- Positively charged CS NPs generation --- p.62 / Chapter 4.2.2 --- Bllb incorporated +ve CS NPs generation --- p.68 / Chapter 4.2.3 --- In vitro release study --- p.70 / Chapter 4.2.4 --- In vitro cytotoxicity test --- p.72 / Chapter 4.3 --- Discussion --- p.74 / Chapter Chapter 5 - --- Generation of negatively charged CS particles and Bllb incorporation --- p.83 / Chapter 5.1 --- Introduction --- p.83 / Chapter 5.2 --- Results --- p.85 / Chapter 5.2.1 --- -ve CS NPs generation --- p.85 / Chapter 5.2.2 --- -ve CS-Bllb NPs generation --- p.88 / Chapter 5.2.3 --- In vitro release study --- p.91 / Chapter 5.2.4 --- Localization study of -ve CS-Bllb NPs --- p.93 / Chapter 5.2.5 --- In vitro cytotoxicity test --- p.96 / Chapter 5.3 --- Discussion --- p.98 / Chapter Chapter 6 - --- Conclusion and future work --- p.108 / Copyright --- p.110 / References --- p.111

Nanostructured metallic multilayers (NMMs) are well-known for their high strength in smaller bilayer thicknesses. Six Al/Ti (NMM) with different individual layer thickness were tested for their mechanical hardness using a nanoindentation tool. Individual layer thicknesses were chosen carefully to cover the whole confined layer slip (CLS) model. Nano-hardness had a reverse relation with the square root of individual layer thickness and reached a steady state at ~ 5 nm bilayer thickness. Decreasing the layer bilayer thickness from ~ 104 nm to ~ 5 nm, improved the mechanical hardness up to ~ 101%. Residual stresses were measured using grazing incident X-ray diffraction (GIXRD). Effect of residual stress on atomic structure and dislocation propagation was then investigated by comparing the amount and type of stresses in both aluminum and titanium phases. Based on the gathered data from GIXRD scans tensile stress in Ti phases, and compressive stress in Al would increase the overall coherency of structure. Wear rate in coatings is highly dependent on design and architect of the structure. NMM coatings are known to have much better wear resistance compare to their monolithic constituent phases by introducing a reciprocal architect. In current study wear rate of two Al/Ti NMMs with individual layer thicknesses of ~ 2.5 nm and ~ 30 nm were examined under normal loads of 30 µN, 60 µN, and 93 µN. Wears strokes were performed in various cycles of 1, 2, 3, 4 5 and 10. Wear rates were then calculated by comparing the 3D imaging of sample topology before and after tests. Nano-hardness of samples was measured pre and post each cycle of wear using a nanoindentation tool. The microstructure of samples below the worn surface was then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), focus ion beam (FIB) and an optical profilometer. Orientation mapping was performed to analyze the microstructure of layers beneath the nano indents. TEM imaging from the cross section of worn samples indicated severely plastically deformed layer (SPDL) below the worn surface. Shear bands and twins are visible after wear and below the worn surface. Decreasing the layer thickness from 30 nm to 2.5 nm resulted in ~ 5 time’s better wear resistance. Nanowear caused surface hardening which consequently increased nano hardness up to ~ 30% in the sample with 2.5 nm individual layer thickness. Increasing the interfaces density of NMMs will significantly improve the corrosion resistance of coating. Reciprocal layers and consequently interfaces will block the path of aggressive content toward the substrate. Corrosion rate evolution of Al/Ti multilayers was investigated through DC corrosion potentiodynamic test. Results seem to be very promising and demonstrate up to 30 times better corrosion resistance compared to conventional sputtered monolithic aluminum. Corrosion started in the form of pitting and then transformed to the localized galvanic corrosion. Decreasing the bilayer thickness from ~ 10.4 nm to ~ 5 nm will decrease the corrosion current density (icorr) of ~ 5.42 × 10-7 (A/cm2) to ~ 6.11 × 10-10 (A/cm2). No sign of corrosion has been seen in the sample with ~ 2.5 nm individual layer thickness. Further AFM and TEM analysis from surface and cross section of NMMs indicate that a more coherent layer by layer structure improves the corrosion rate. Interfaces have a significant role in blocking the pores and imperfections inside coating.

Carbon nanotubes have excellent potential as basic building blocks for nanometer scale electron devices. Of particular interest in this context are their electron transport properties at high electric fields and at ambient temperature. Because the envisioned device switching times are very short and device dimensions small, not only steady-state, but also transient phenomena need to be explored. In this study are presented results of ensemble Monte Carlo simulations for carbon nanotubes, focusing particularly on semiconducting, single wall, zigzag (n,0) structures of wide ranging diameters. The basis for the Monte Carlo simulations are electronic structure calculations in the framework of a tight binding model. The principal scattering mechanism considered is due to the electron-phonon interaction. From the ensemble Monte Carlo simulation we determine the evolution of the electron distribution function as a function of position and time. Interesting behavior, not observed in conventional semiconducting materials, are observed in carbon nanotubes. The results presented help to place bounds on the device speeds that may be expected, and support the potential of semiconducting carbon nanotubes for high-speed electron device applications.

The UV-Visible spectra of a-C composites and nano composites have provided a very useful information about the electronic states and band structure. The UV-Visible spectra of a-C as well as nanoparticle are qualitatively similar. They do not show any absorption cutoff in wavelength (_max). In fact they are good absorbers of UV-Visible light in whole range. Composites show some absorptions which could be the combined effect of filler as we as host matrix. Since there is no _max, hence it is very unlikely to define any optical band gap. The nanoparticle is a good absorber in midinfrared compared to a-C. That may be due to presence of complicated kind of vibrational modes of carbon cased nanoparticle.Besides Fe3C also produces some additional modes. With kind of spectrum we have it is difficult to identify the different modes unambiguously for nanoparticle. The combined effects of filler as well as host polymer are reflected in both sets of composites. A new absorption is observed in a-C as well as in nanoparticle composites at 2370 cm−1 and 3462 cm−1 respectively. This peak may arise in composites due to interaction between filler and host matrix. The thermo gravimetric analysis is a useful characterization techniques for polymer and composites. It gives the information about the stability, phase change, degradation, chemical reaction and many more. The a-C composites as well as nano composites are stable up to 200_ C. These composites can be safely used for any practical purpose below this temperature. During the synthesis of composites the filler does not take part in any reaction. This fact is reflected in the DTG curve. The composites degrade in the way host polymer degrades.