Presentation description

Homochirality, where one enantiomer dominates over the other, plays a crucial role in biological and chemical. Understanding which enantiomer interacts with biological targets is vital for drug design. In the wake of the thalidomide incident, the Food and Drug Administration created a policy requiring the complete configuration of chiral compounds to be known. The issue with detecting chiral molecules is that their signals are too small to be interpreted when using optical techniques. Plasmonics offers a new method of identification by enhancing the optical responses of the molecules of interest. Localized surface plasmon resonance (LSPR) is the collective oscillations of conduction electrons on metallic nanostructured surfaces and can be measured in the ultraviolet-visible and infrared spectrum. Gold nanocrescents (NCs) with ranging sizes were previously fabricated with LSPR in mind as structures with sharp tips enhance the electromagnetic field (EM) surrounding the crescents. To identify the most suitable NCs for experiments with chiral molecules, samples were analyzed based on their extinction when oriented at non-normal angles to the incident light. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to conduct three- and two-dimensional measurements of the size and height of the structures. Ultraviolet-visible spectroscopy was utilized to determine the LSPR of NCs of varying sizes. Using linearly polarized light, each sample was rotated -30, 0, and +30 degrees with respect to the incident light. Of the NC samples analyzed, two of the samples showed promising LSPR spectra with strong plasmon bands and high extinction. We found that all samples exhibited the highest extinction at rotations of +/-30° resulted in negligible differences between the two angles. These results help us determine what physical properties and structural orientation may be beneficial for developing nanocrescents for chiral molecule detection.