Browsing by Author "Mikkola, Kalle"

This thesis examines the optical response of tuneable chiral plasmonic nanostructures in linear cross-polarization. Plasmonic gold-silver nanostructures composed of silver-coated gold nanorods, and dynamic DNA origami are investigated because of their optical properties of interest in the visible light wavelength region, and because of their controllable rotational asymmetry, which results in tuneable chirality in dimer structures. These plasmonic nanostructures present optical properties such as circular dichroism and optical rotatory dispersion. In this thesis we establish the relationship between perceived color, spectrometry, circular dichroism and optical rotatory dispersion of the samples, depending on the chiral geometry of the nanostructures within. The motivation is to predict perceived color from the chiral geometry of the nanostructures, which will enable visual detection for biosensing applications. Circular dichroism and optical rotatory dispersion give us detailed knowledge about the polarization state of a sample, but visible light detection and spectrometer measurements are more accessible and portable methods for characterizing the polarization state of a sample. We achieve color modulation from green to blue with the switching of chiral geometry, under cross-polarized white light. This has potential for biosensing applications, based on the perceived color change depending on the chiral geometry of the sample. The DNA origami structures react to the presence of an analyte by changing their chiral geometry. Possible applications in biosensing of analytes can be made more practical if the orientation of the DNA origami template can be determined from the perceived color or the transmission spectra, rather than from the less accessible circular dichroism or optical rotatory dispersion measurements.