Correlography of randomly scattered surface plasmons for quantitative biology

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Life is a highly complex system that, despite an ever-growing pool of research is still poorly understood. Advances in the life sciences, enabled by constant innovation in experimental techniques, fuel an increasingly higher quality of life through drug development, rapid diagnostics and improved healthcare. Fuller understanding of the science of life, however, requires the temporal dynamics of biological processes to be monitored and the characteristics of single molecule to be quantitatively analysed. Light is an invaluable tool in the quest to reach this goal. More recently, coupled electronic-optical oscillations in metal nanostructures and films, simply known as plasmons, have also played an increasingly important role, allowing stronger light-matter interactions and strong field confinement. "Plasmon speckle" patterns, which are strongly spatially fluctuating fields, arise when many plasmons randomly interfere with each other. Such speckle patterns can be formed at metal interfaces due to scattering from inherent surface roughness or bound nanoparticles. Through the cumulative effect of multiple interfering plasmons, plasmon speckle possesses an extreme sensitivity to the local environment and the scattering configuration, which is further enhanced when plasmons scatter many times. This project will explore principles by which biosensing, i.e. detection of biomolecules, can be achieved by measuring changes in the plasmon speckle. For example, binding of individual biomolecules, can manifest as large step-like changes in the correlation of optical speckle patterns resulting from inelastic plasmon scattering. Moreover, dynamic biological processes, such as molecular reactions or conformational changes, cause plasmon speckle to fluctuate in time in a way that strongly depends on the molecular properties, interaction kinetics and local trapping forces, providing a powerful route to studying particle size, mobility and binding dynamics. The core focus of this project is thus to establish correlation based techniques, akin to dynamic light scattering, on a surface plasmon based sensor.