Synthesis, Structural and Magnetic Properties of Copper Doped Cerium Oxide Nanoparticles

In this thesis, synthesis, structural and magnetic properties of the undoped and copper doped cerium oxide nanoparticles have been investigated. The nanoparticles were prepared by sol-gel preparation method. Undoped samples were prepared with different particles sizes by annealing the as-prepared sample at different temperatures Ta = 200°C, 400°C, 550°C, 700°C, 800°C. The particle size varied from 3 nm to 42 nm with increasing annealing temperatures. Copper was doped into CeO2 by annealing the samples at 400°C in ultra high pure nitrogen. The nominal percentages of copper in doped cerium oxide were 2.5%, 5%, 7.5% and 10%.;Structural characterization of the nanoparticles was done using transmission electron microscope (TEM) and x-ray diffraction (XRD). Inductive coupled plasma optical emission spectroscopy was done to detect the impurity concentrations of Iron (Fe) which was found to be present in ppm levels. The nano-particles were found to be nearly spherical in shape in both undoped and doped samples. The particle sizes in undoped samples were found to be increasing with increase in annealing temperatures. As all the copper doped samples were annealed at same temperatures, they were all in the 5 nm size range. The particle size values from XRD and TEM were comparable. Lattice constant and the strain in undoped CeO2 nanoparticles was found to decrease with increase in particle size. In Cu-doped CeO2, lattice constant was increasing with increase in doping concentration levels.;Magnetic properties of these nanoparticles were measured using a superconducting quantum interface device (SQUID) magnetometer. Susceptibility and hysteresis loops plots were plotted using magnetization data from SQUID. Increasing paramagnetism was found with decreasing particle size in the undoped samples which is attributed to increase in Ce3+ concentration. The small amount of ferromagnetism found in the undoped samples is suggested to originate from the Fe present in ppm levels. In Cu-doped CeO2 nanoparticles, the paramagnetic and ferromagnetic parts were found to be increasing with increase in doping concentration of Cu in CeO2. The observed room temperature ferromagnetism in Cu-doped CeO2 is suggested to result from the effects of copper doping

Fabrication of Nanoelectrode Arrays for Dopamine Detection

Recent advancements in the semiconductor fabrication technologies have greatly helped in advancing the understanding of electrochemistry at nano scale (10-9 m). Electrodes are being produced at micro (10-6 m) and nano scale with varied materials, designs and for diverse applications. Better electrochemical sensing and detecting capabilities are achieved with nanoelectrodes in comparison with regular macroelectrodes. Lot of theoretical studies of electrochemistry at these nanoelectrodes have been proposed and developed. Despite the theoretical advancements, little has been done in experimental studies of nanoelectrodes. The progress is majorly impeded by lack of reliable fabrication procedures to produce such nanoelectrodes and test them experimentally.;The main goal of this thesis is to develop a new procedure to fabricate nanoelectrode arrays (NEA) for enhanced electrochemical detection. A large area gold NEA is fabricated using nanosphere lithography. The electrochemical advantages of the nanoelectrodes over macro electrodes such as better mass transport of analytes, independent diffusional domains, and faster chemical reaction rates are studied. The dimensions of the electrode are optimized to get the best possible electrochemical sensing capabilities. The optimized NEA is used as a biological sensor for detecting dopamine, a neurotransmitter, in presence of biological levels of ascorbic acid.;The optimized NEA geometry has shown an excellent ability to differentiate and detect the dopamine in presence of high levels of ascorbic acid. This is attributed to the enhanced mass transport of analytes and faster chemical reaction rates at the surface of the nanoelectrodes. Bare gold macroelectrode of similar exposed area has failed to differentiate the dopamine and ascorbic acid signals

Plasmonic Nanorice Antenna on Triangle Nanoarray for Surface-Enhanced Raman Scattering Detection of Hepatitis B Virus DNA

The sensitivity and the limit of detection of Raman sensors are limited by the extremely small scattering cross section of Raman labels. Silver nanorice antennae are coupled with a patterned gold triangle nanoarray chip to create spatially broadened plasmonic “hot spots”, which enables a large density of Raman labels to experience strong local electromagnetic field. Finite difference time domain simulations have confirmed that the quasi-periodic structure increases the intensity and the area of the surface plasmon resonance (SPR), which enhances the surface-enhanced Raman scattering (SERS) signal significantly. The SERS signal of the nanorice/DNA/nanoarray chip is compared with that of the nanorice/DNA/film chip. The SERS signal is greatly enhanced when the Ag nanorices are coupled to the periodic Au nanoarray instead of the planar film chip. The resulting spatially broadened SPR field enables the SERS biosensor with a limit of detection of 50 aM toward hepatitis B virus DNA with the capability of discriminating a single-base mutant of DNA. This sensing platform can be extended to detect other chemical species and biomolecules such as proteins and small molecules

Detection of Adenosine Triphosphate with an Aptamer Biosensor Based on Surface-Enhanced Raman Scattering

A simple, ultrasensitive, highly selective, and reagent-free aptamer-based biosensor has been developed for quantitative detection of adenosine triphosphate (ATP) using surface-enhanced Raman scattering (SERS). The sensor contains a SERS probe made of gold nanostar@Raman label@SiO₂ core–shell nanoparticles in which the Raman label (malachite green isothiocyanate, MGITC) molecules are sandwiched between a gold nanostar core and a thin silica shell. Such a SERS probe brings enhanced signal and low background fluorescence, shows good water-solubility and stability, and exhibits no sign of photobleaching. The aptamer labeled with the SERS probe is designed to hybridize with the cDNA on a gold film to form a rigid duplex DNA. In the presence of ATP, the interaction between ATP and the aptamer results in the dissociation of the duplex DNA structure and thereby removal of the SERS probe from the gold film, reducing the Raman signal. The response of the SERS biosensor varies linearly with the logarithmic ATP concentration up to 2.0 nM with a limit of detection of 12.4 pM. Our work has provided an effective method for detection of small molecules with SERS

Three-Dimensional Hierarchical Plasmonic Nano-Architecture Enhanced Surface-Enhanced Raman Scattering Immunosensor for Cancer Biomarker Detection in Blood Plasma

A three-dimensional (3D) hierarchical plasmonic nano-architecture has been designed for a sensitive surface-enhanced Raman scattering (SERS) immunosensor for protein biomarker detection. The capture antibody molecules are immobilized on a plasmonic gold triangle nanoarray pattern. On the other hand, the detection antibody molecules are linked to the gold nanostar@Raman reporter@silica sandwich nanoparticles. When protein biomarkers are present, the sandwich nanoparticles are captured over the gold triangle nanoarray, forming a confined 3D plasmonic field, leading to the enhanced electromagnetic field in intensity and in 3D space. As a result, the Raman reporter molecules are exposed to a high density of “hot spots”, which amplifies the Raman signal remarkably, improving the sensitivity of the SERS immunosensor. This SERS immunosensor exhibits a wide linear range (0.1 pg/mL to 10 ng/mL) and a low limit of detection (7 fg/mL) toward human immunoglobulin G protein in the buffer solution. This biosensor has been successfully used for detection of the vascular endothelial growth factor in the human blood plasma from clinical breast cancer patient samples

Photocatalytic Activity Enhanced by Plasmonic Resonant Energy Transfer from Metal to Semiconductor

Plasmonic metal nanostructures have been incorporated into semiconductors to enhance the solar-light harvesting and the energy-conversion efficiency. So far the mechanism of energy transfer from the plasmonic metal to semiconductors remains unclear. Herein the underlying plasmonic energy-transfer mechanism is unambiguously determined in Au@SiO₂@Cu₂O sandwich nanostructures by transient-absorption and photocatalysis action spectrum measurement. The gold core converts the energy of incident photons into localized surface plasmon resonance oscillations and transfers the plasmonic energy to the Cu₂O semiconductor shell via resonant energy transfer (RET). RET generates electron–hole pairs in the semiconductor by the dipole–dipole interaction between the plasmonic metal (donor) and semiconductor (acceptor), which greatly enhances the visible-light photocatalytic activity as compared to the semiconductor alone. RET from a plasmonic metal to a semiconductor is a viable and efficient mechanism that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices