UC Irvine

Detection, characterization and separation of chiral structures as one of the fundamental constituents of biomolecules are crucial in chemical and biological applications. Conventionally, chiroptical techniques such as circular dichroism (CD) are exploited to identify the material chirality. These methods require substantial amount of sample material with a high concentration. since chirality effect (as an indirect electric to magnetic coupling between incident light and sample material) is typically very weak. Therefore, the observation of chirality might be masked under the electric properties in chiroptical techniques if a substantial amount of material is not provided. Consequently, these techniques are not suitable for detection of chirality for nanoscale samples and can’t provide information about their primary or secondary structure. On the other hand, separation of enantiomers is of great interest in pharmaceutical applications. Classical separation techniques which are used to separate molecular compounds and complexes in achiral environment, such as liquid-liquid extraction, chromatography and distillation are not universal for separation of all types of chiral molecules/compounds since not all compounds and host media are chemically compatible. This dissertation focuses on introducing new techniques for detection, characterization and manipulation of chiral nanoparticles and nanostructures using structured light. Specifically, a new technique involving the measurement of photo-induced optical force (near-field characteristics) rather than the measurement of conventional scattered power (far-field characteristics) is introduced which substantially enhances the resolution in the detection of enantiomer type of chiral samples down to sub-100 nm. Furthermore, by utilizing structured illumination (circularly polarized wave for detection of transverse chirality and combination of azimuthally and radially polarized waves in the so-called azimuthally-radially polarized beam for detection of longitudinal chirality) the prediction of spatial features of the structure of a chiral sample is facilitated. It’s been demonstrated that circularly polarized illumination can’t differentiate between chirality and anisotropy. To overcome this deficiency and differentiate between anisotropy and chirality, an engineered combination of vortex beams (ARPB) is utilized. Lastly, a novel scheme to manipulate and control chiral nanoparticles and to sort enantiomers is proposed.