Not available / text

Not available / text

Not available / text

Label-free detection techniques have an important role in many applications, such as situations where few molecules -- rather than low molarity -- need to be detected, such as in single-cell screening. While surface plasmon resonance (SPR) scattering from metal nanoparticles has been shown to achieve significantly higher sensitivity in gene arrays, such an approach has not been demonstrated for protein arrays. SPR-based sensors could either use simple absorption measurement in a UV-Vis spectrometer or possibly surfaceenhanced Raman spectroscopy as the detection mechanism for molecules of interest. However, non-spherical particles are needed to achieve high sensitivity and field enhancement that is a requirement in both techniques, but these shapes are not easy toproduce reproducibly and preserve for extended periods of time. Here I present a carbonbased template-stripping method combined with nanosphere lithography (NSL). This fabrication allows to preserve the sharp features in atomically flat surfaces which are a composite of a non-spherical metal nano-particle (gold or silver) and a transparent embedding material such as glass. The stripping process is residue-free due to the introduction of a sacrificial carbon layer. The nanometer scale flat surface of our template stripping process is also precious for general protein absorption studies, because an inherent material contrast can resolve binding of layers on the 2 nm scale. These nanocomposite surfaces also allow us to tailor well-defined SPR extinction peaks with locations in the visible or infrared spectrum depending on the metal and the particle size and the degree of non-symmetry. As the particle thickness is reduced and the particle bisector length is increased, the peak position of the resonance shifts to the red. Not only the peak position shifts, but also the sensitivity to environmental changes increases. Therefore, the peak position of the resonance spectrum is dependent on the dielectric environmental changes of each particle, and the particle geometries. The resulting silver or gold nanoparticles in the surface of a glass slide are capable of detecting thiol surface modification, and biotin-streptavidin protein binding events. Since each gold or silver particle principally acts as an independent sensor, on the order of a few thousand molecules can be detected, and the sensor can be miniaturized without loss of sensitivity. UNSL-Au metal nanoparticle (MNP) sensors achieve the sensitivity of close to 300 nm/RIU which is higher than any other report of localized surface plasmon resonance (LSPR) sensors except gold nanocrescents. Finite-difference-time-domain (FDTD) and finite-element-method (FEM) numerical calculations display the influence of the sharp features on the resonance peak position. The maximum near-field intensity is dependent on the polarization direction, the sharpness of the feature, and the near-field confinement from the substrate. 3D FDTD simulation shows the local refractive index sensitivity of the gold truncated tetrahedron, which is in agreement with our experimental result. Both experimental and numerical calculations show that each particle can act as its own sensor.

Conventional MRI relies on a strong fixed magnetic field B0 which is stable during the imaging process. By contrast, field-cycling MRI switches the strength of B0 up or down during an experiment. In this way, field-cycling provides access to endogenous information not accessible to standard MRI, such as enhanced T1 relaxation at certain NMR frequencies due to interactions between hydrogen and nitrogen nuclei in proteins. However, biomedical research of T1 dispersion is limited by the unavailability of equipment and rapid software methods. Strategies are presented to address these deficiencies. A removable electromagnet was designed and implemented for use with a 59-mT vertical-field, permanent-magnet based imager. The resistive magnet locally offsets the primary field over a small projected region to enable field-cycling relaxometry on an otherwise-conventional imager. Radiofrequency coils were constructed to suit the electromagnet’s configuration. T1 dispersion measurements were demonstrated for, separately, the finger joints and forearm of a human volunteer. Prior to this work, producing graphs of T1 dispersion from a volume of interest required lengthy T1 mapping at each field strength step. A new pulse sequence combining SR/IR T1 determination with field-cycling and point-resolved spectroscopy localization enables the measurement of dispersion curves of a volume selected from a pilot image. Its advantages include less partial voluming than whole-sample relaxometry, as well as better SNR and faster acquisition times than image-based techniques. The sequence’s sensitivity is sufficient to reveal distinctive ‘quadrupole dips’ in dispersion curves. To the author’s knowledge, it is the first pulse sequence to enable the relationship between T1 and field strength to be examined in times which are feasible for clinical investigations. Used together as presented in this thesis, the hardware and software developed represent a step towards field-cycling being used to reveal useful diagnostic information inaccessible to conventional MRI.

Not available / text

Not available / text

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

No description available.

No description available.