Low-molecular-mass small molecules play important roles in biological processes and often serve as disease-related biomarkers for diagnosis. Accurate detection of small molecules remains challenging for conventional sensors due to their limited sensitivities. Two-dimensional (2D) materials, thanks to their atomic level thickness, can be extraordinarily sensitive to external perturbations and therefore well-suited for sensing applications. This dissertation explores the use of 2D materials, including primarily graphene and transition metal dichalcogenides, in the detection of low-molecular-weight and low-charge molecules. This work starts with the study of methods that allow for efficient and clean transfer of graphene grown on Cu using chemical vapor deposition (CVD), which is a critical step for achievement of large-area and high-quality graphene for device fabrication. In addition to the conventional wet-etching transfer method, we have studied on the method of electrochemical delamination, which is more time-efficient and allows for recycling of the Cu foil. Generation of bubbles during the electrochemical reaction is minimized by tuning the experimental parameters, thereby minimizing transfer-induced damages to graphene. We then fabricate the graphene-based field effect transistor (FET) and use the graphene FET as biosensors. First, the sensor is configured as an electrolyte-gated FET. With appropriate biochemical functionalization of the graphene, the FET sensors have been used to detect multiple small-molecule biomarkers including glucose and insulin via their affinity binding with receptors. Then, on a flexible substrate, we demonstrate real-time measurement of tumor necrosis factor alpha, a signal protein that regulates immune cells. We then simplified the sensor structure using a bottom local-gate to replace the external electrode as required in the previous electrolyte gated FET. Using the bottom local-gated FET sensor we have carried out real-time monitoring of the variation of pH in solutions. In addition to the electrical sensors, highly sensitive and multifunctional plasmonic sensors have also been developed by combining the unique optical properties of graphene with engineered metallic metasurfaces. The plasmonic sensors operating in mid-infrared region are configured as either metallic metasurface or hybrid graphene-metallic metasurface. Using a metallic metasurface, we demonstrate simultaneous quantification and fingerprinting of protein molecules. Using a hybrid graphene-metallic metasurface, we demonstrate optical conductivity-based ultrasensitive biosensing. In contrast to refractive-index-based sensors, the sensitivity of the hybrid metasurface sensor is not limited by the molecular masses of analytes. A monolayer of the sub-nanometer chemicals can be readily detected and differentiated on the hybrid metasurface. Reversible detection of glucose is carried out via the affinity binding of glucose with boronic acid immobilized on the graphene of the hybrid metasurface. The lowest detection limit achieved in our work is 36 pg/mL, which is considerably lower than that for the existing optical sensors. Despite the high sensitivity of graphene, the zero band-gap of graphene fundamentally impedes its use in digital electronic devices. In contrast, two-dimensional semiconductors, such as transition metal dichalcogenide (TMDC) with non-zero band gaps, holds great potential for developing practical electronic devices and sensors. Monolayers of TMDC materials are particularly attractive for development of deeply scaled devices, although the contact resistance between metal and the monolayer TMDC has been so large to significantly limit the performance of the devices. We present a high-performance monolayer MoS2 FET with a monolayer graphene as bottom local gate. The graphene gate is found to significantly improve the dielectric strength of the oxide layer compared to the lithographically patterned metal gate. This in turn allows for the use of very thin gate dielectric layer (~5 nm) and application of a strong displacement field to lower the contact resistance. Benefiting from the low contact resistance, the monolayer MoS2 FET offers a high on/off ratio (108) and low subthreshold slope (64 mV/decade). Additionally, thanks to the highly efficient electrostatic coupling through the ultrathin gate dielectric layer, short-channel (50 nm and 14 nm) devices are realized that exhibit excellent switching characteristics. In summary, this dissertation presents significant contributions to 2D material-based electronic and optoelectronic nanosensors, especially for detection of small molecules. Perspectives are made in the end of the thesis, on future studies needed to realize practical applications of these sensors and other 2D material-based products.

In this study, two kinds of effective VLD photocatalysts, AgBr-Ag-Bi 2WO6 nanojunction and Zn:In(OH)ySz solid solution nanoplates have been synthesized and characterized. Zn:In(OH) ySz solid solution nanoplates (Synthesis conditions: 45 mmol L-1 thiourea, 26 mmol L-1 SDS, 0.4≤X≤0.7) have high VLD photocatalytic activities on the degradation of Rhodamine B (RhB), which is due to their suitable band gap and potentials of conduction band and valence band as well as their uniform and small diameter sizes (about 10 nm in width and about 15 nm in length). AgBr-Ag-Bi2WO6 nanojunction exhibits excellent VLD photocatalytic performance both on the degradation of Procion Red MX-5B and pentachlorophenol, and on the disinfection of various bacteria including Escherichia coli, Pseudomonas fluorescens and Alteromonas macleodii. Its excellent performance results from the broadened visible-light response and the synergic effect among the three components under the visible light irradiation, namely the vectorial electron transfer of Bi2WO6→Ag→AgBr. / Moreover, a novel and versatile partition setup has been first constructed to investigate the fundamental mechanism of photocatalytic process. The results indicate that the functional reactive species produced by VLD Zn:In(OH) ySz solid solution nanoplates mainly remain on the surface, thus the direct contact between Zn:In(OH)ySz solid solution nanoplates and RhB is a prerequisite for the degradation of RhB during the photocatalytic process. However, the functional reactive species produced by AgBr-Ag-Bi2WO6 nanojunction can diffuse into the bulk, thus the direct contact between the AgBr-Ag-Bi2WO6 nanojunction and bacteria is unnecessary for the photocatalytic disinfection of bacteria. / Recent years, environmental problems related to organic pollutants and pathogenic microorganisms have emerged as a high national and international priority. To address these significant problems, photocatalysis causes increasing interest as a kind of green and energy-saving technology. However, the traditional photocatalyst TiO2 can only be excited by ultraviolet or near-ultraviolet radiation, which merely occupies about 4% of the solar light spectrum. Notably, the visible region covers the largest proportion of the solar spectrum (about 48%). In order to efficiently utilize solar light, the development of visible-light-driven (VLD) photocatalysts with excellent performances has been urged. / Therefore, in this work, the exploration of VLD photocatalyst gives us the opportunities to utilize solar energy to solve the environmental problems and energy crisis, and the investigation of fundamental mechanism provides us more deep understanding for photocatalytic process. / Zhang, Lisha. / Adviser: P. K. Wong. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 159-171). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

abstract: Medulloblastoma is the most common malignant pediatric brain cancer and is classified into four different subgroups based on genetic profiling: sonic hedgehog (SHH), WNT, Group 3 and 4. Changes in gene expression often alter the progression and development of cancers. One way to control gene expression is through the acetylation and deacetylation of histones. More specifically in medulloblastoma SHH and Group 3, there is an increased deacetylation, and histone deacetylase inhibitors (HDACi) can be used to target this change. Not only can HDACi target increases in deacetylation, they are also known to induce cell cycle arrest and apoptosis. The combination of these factors has made HDACi a promising cancer therapeutic. Panobinostat, a hydrophobic, small molecule HDACi was recently identified as a potent molecule of interest for the treatment of medulloblastoma. Furthermore, panobinostat has already been FDA approved for treatment in multiple myeloma and is being explored in clinical trials against various solid tumors. The laboratory is interested in developing strategies to encapsulate panobinostat within nanoparticles composed of the biodegradable and biocompatible polymer poly(lactic acid)-poly(ethylene glycol) (PLA-PEG). Nanoparticles are formed by single emulsion, a process in which hydrophobic drugs can be trapped within the hydrophobic nanoparticle core. The goal was to determine if the molecular weight of the hydrophobic portion of the polymer, PLA, has an impact on loading of panobinostat in PLA-PEG nanoparticles. Nanoparticles formulated with PLA of varying molecular weight were characterized for loading, size, zeta potential, controlled release, and in vivo tolerability. The results of this work demonstrate that panobinostat loaded nanoparticles are optimally formulated with a 20:5kDa PLA-PEG, enabling loading of ~3.2 % w/w panobinostat within nanoparticles possessing an average diameter of 102 nm and surface charge of -8.04 mV. Panobinostat was released from nanoparticles in a potentially biphasic fashion over 72 hours. Nanoparticles were well tolerated by intrathecal injection, although a cell culture assay suggesting reduced bioactivity of encapsulated drug warrants further study. These experiments demonstrate that the molecular weight of PLA influences loading of panobinostat into PLA-PEG nanoparticles and provide basic characterization of nanoparticle properties to enable future in vivo evaluation. / Dissertation/Thesis / Masters Thesis Biomedical Engineering 2019

Diffractive optical elements (DOEs) are thin, light-weight devices capable of shaping light both spatially and spectrally. Classical light is a multivariate vector field: at each wavelength and at each point in space, it is characterized an amplitude and phase for two orthogonal polarizations. “Metasurfaces” are a class of DOEs composed of subwavelength structures engineered to alter a featureless wavefront into a custom wavefront; a multivariate metasurface may control several parameters simultaneously and independently. If limited to low-loss dielectric materials, metasurfaces promise functionalities and efficiencies unparalleled in other DOEs, and are manufacturable by mature micro- and nanofabrication methods. Here, we expand the capabilities of metasurfaces to generate multivariate wavefronts. By engineering both the phase and the phase dispersion, we experimentally demonstrate metasurfaces focusing light to a single point independently of wavelength or polarization. By tuning the structural birefringence and in-plane orientation angle of rectangular nanostructures, we experimentally demonstrate arbitrary control of both phase and amplitude, enabling holography as it was originally envisioned. By maximizing the in-plane Bragg scattering of a Photonic Crystal Slab, and then successively adding symmetry-breaking perturbations to the otherwise perfect lattice, we may control angular dependence, optical lifetime, and polarization dependence of up to four optical resonances simultaneously and independently (which we study using Group Theory and fullwave simulations). By spatially varying the perturbations, the wavefronts at the resonance frequencies may be spatially tailored while the non-resonant frequencies are unaffected, promising DOEs uniquely suitable for augmented reality applications.

Graphene is a recently created truly two-dimensional carbon material with promising properties. It is a prospective candidate for the next generation of microelectronics. Current carriers in graphene have relativistic properties, its lattice is very strong and yet flexible, granting graphene's ballistic conductivity on the submicron scale at the room temperatures. Midgap bound state induced by a single impurity in graphene does not cause essential changes in the electronic liquid distribution at all reasonable values of the coupling strength. Thus there are no unusual screening effects predicted for the graphene with long-range Coulomb impurity. This result holds in case of multiple impurities localized in the finite area on the lattice. Exact expressions for the lattice Green functions are derived. The absence of critical screening for the short-range impurities in graphene is a main result of the work. Another outcome is the observation of the limitations on the Dirac approximation applicability. / Micro-Electro-Mechanical Systems and Nanosystems

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Nano-sensors, as an application of nanotechnology, are extremely important for environmental, medical and security applications. Terahertz science is an exciting new field that is set to impact the field of sensing to a large extent. I proposed to combine the fields of nanotechnology and terahertz science and develop a molecular nano-sensor that operates at terahertz frequencies. I focused our sensing on energetic materials, particularly nitromethane, and conducted an extensive analysis on its frequency spectrum. The study also focused on designing the nano-sensor and determining its terahertz operation characteristics. I subjected it to various conditions through the use of molecular dynamics simulations. Finally we analyzed the simulation results and provided a proof of the concept that we had a working molecular nano-sensor that operates at terahertz frequencies and senses energetic materials. The results from the frequency analysis of nitromethane showed that the frequency characteristics determined from our simulations were in close agreement with the ones determined experimentally. In addition to this we also successfully demonstrated the use of a Lennard Jones potential to model the CN bond scission of nitromethane. Finally, the results from the interactions between the nano-sensor and nitromethane showed that the presence of nitromethane causes sufficient change in the terahertz frequency characteristics of the nano-sensor providing a means to detect nitromethane.

<p>This work entails the preparation of various polyanilines with different morphologies and their application in photovoltaic solar cells. Zinc oxide (ZnO) with one-dimensional and flower-like morphology was also prepared by microwave irradiation and used as electron acceptors in photovoltaics devices. The morphological, structural, spectroscopic and electrochemical characteristics of these materials were determined by scanning electron microscopy (SEM), X-Ray diffraction (XRD), Raman, Fourier-transformed infrared spectroscopy (FTIR), ultraviolet and visible spectroscopy (UV-Vis), photoluminescence(PL), thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) experiments. Devices fabricated from these materials were characterized under simulated AM 1.5 at 800 mW.</p>

<p>The objective of this research was to develop highly efficient and yet effective MnO2 electrode materials for supercapacitors applications. Most attention had focussed on MnO2 as a candidate for pseudo-capacitor, due to the low cost of the raw material and the fact that manganese is more environmental friendly than any other transition metal oxide system. The surface area and pore distribution of MnO2 can be controlled by adjusting the reaction time. The MnO2 synthesised under optimum conditions display high capacitance, and exhibit good cycle profile. This work investigates the ways in which different morphological structures and pore sizes can affect the effective capacitance. Various -MnO2 were successfully synthesised under low temperature conditions of 70 oC and hydrothermal conditions at 120 oC. The reaction time was varied from 1 to 6 hours to optimise the conditions. KMnO4 was reduced by MnCl.H2O under low temperature, whereas MnSO4.4H2O, (NH4)2S2O8 and (NH4)2SO4 were co-precipitated under hydrothermal conditions in a taflon autoclave to synthesise various -MnO2 nano-structures.</p>

Lipid bilayer membranes are ubiquitous in biology and electrostatics play a key role in their functionality. The interfacial electrostatics of lipid bilayers involves interplay between the surface potential and charge regulation in the form of ion binding, protonation and lipid mobility. Mobile lipid charge regulation in particular is unique to lipid interfaces and is thought to be an important factor in charged macromolecule-membrane interactions. We used Atomic Force Microscopy (AFM) for the first nanometer scale experimental demonstration of mobile lipid charge regulation occurring in supported lipid bilayer membranes. By combining finite element computer simulations and experimental AFM data, we showed that mobile lipid charge regulation accounts for the short range deviations from the expected electrostatics over anionic lipids. We also accounted for van der Waal interactions and electrolyte ion binding in our calculations and found the mobility of the lipid to be the dominant factor in the short range deviations. Control experiments on silicon nitride surfaces, whose surface charges are immobile, showed that the short range deviation could be accounted for by the formation of a stem layer due to cation binding. Further evidence for tip-induced mobile lipid charge regulation was presented in the form of clear differences in the short range electrostatics of mobile fluid phase lipids when compared to immobile gel phase lipids. Furthermore, our data confirmed the theoretically predicted differences between surfaces containing mobile versus immobile charges.