title: Plasmonic spectroscopy of biomacromolecules with chiral metamaterial
Creators: name: Rodier, Marion
Publisher: name: University of Glasgow
Year: 2020
Subjects: subject: Plasmonic spectroscopy, metamaterial, chirality, biosensing.

description: This thesis explores the applications of injection-moulded chiral plasmonic nanostructures for biomolecules sensing. Such nanostructures enhance the chiroptical signal generated by chiral objects with plasmonic fields. These fields can produce a greater asymmetry than circularly polarised light and are called “Superchiral” fields. They are a very efficient tool for the detection of higher order structures (tertiary, quaternary) in proteins. Subsequently plasmonic metamaterials used for sensing will be introduced. We will demonstrate that the chiral fields they generate, are sensitive to the orientation of the biomolecular material at the surface and the conformation of biomolecular complexes, and that they can sense highly symmetrical structures such as viruses. In the first results chapter it will be shown that the chiral fields are highly sensitive to the surface charges of a protein. It will be shown that the surface charges of the analyte can enhance or reduce the chiral fields depending on the handedness of the fields and the state of charge of the analyte. This new property of the chiral structures leads to several applications in biology. This effect is characterised by a new type of asymmetry in the optical rotatory dispersion (ORD) spectra, thus a new asymmetry parameter will be introduced. This offers a route to rapid determination of the isoelectric points of proteins without prior knowledge of their primary sequences. It can also help to predict protein solubility in solution, their folding and interactions with other biomolecules. The new asymmetry parameter will be shown to be sensitive to the geometry of protein-protein complexes and therefore to the specificity of an interaction between two proteins. Non-specific interaction leads to isotropic complexes and hence gives a weak chiroptical signal. It is also explained that the new asymmetry parameter, introduced in the first results chapter, is a good indicator of the order of the analyte at the metafilm surface. Furthermore, we will show that this sensitivity for surface charges allows the detection of highly symmetrical biomolecules such as plant viruses. The fingerprint in the ORD for viruses with the same geometry and same size but different isoelectric points is shown to be dissimilar. Another property of the nanostructures is the ability to display plasmonic induced transparency (PIT). The model of the PIT allows the asymmetry to be measured in the phase retardation. This parameter ΔΔφ is shown to be more sensitive to surface charges and hence allows higher accuracy in virus detection. Chiral fields are also efficient in distinguishing between virions and virus-like particles (VLP). The effect of adding a gold binding domain on the virus particles is explored, and proved efficient, even though the chemistry of the virus surface is changed. Finally, chiral fields are used to sense rod-shaped viruses. This chapter emphasizes the sensitivity of the parameters ΔΔφ and raises the problem of the sensitivity limit for bigger macromolecules. The effect on the asymmetry is shown to be dependent on the orientation of the particles. Using the chirality tensor, the detection limit of macro-biomolecules in the chiral fields will be described.