Ricerc@Sapienza

Chirality, a lack of the mirror symmetry of an object, exists in DNA, many amino-acids, sugars, enzymes, and drugs. Specifically, two nonsuperimposable mirror images of the same chiral molecule are called enantiomers. The two enantiomers have the same chemical formula, but the spatial symmetry breaking leads to different effects on human body; e.g. while one enantiomer acts as a drug, the other one can be inactive or even lead to side-effects. Thus, it is important to have a sensor able to detect and distinguish ultra-low enantiomer concentrations (i.e. enantioselectivity), which is difficult as they have most of physical properties equal. Luckily, the chirality leads to different interaction with left and right circularly polarized light (LCP and RCP, respectively), thus photonic components are used for characterization of chiral solutions. However, conventional techniques usually require big volumes, high concentrations and long post-processing. Recently, there has been an interest in mimicking the chiral effects at the nanoscale. Special designs with broken symmetry in nanomaterials lead to their own chirality, and to the enhancement of chirality when they interact with chiral molecules. In this work, we study chiral substrates fabricated by low-cost nanosphere lithography. Arrays of tilted elliptic nanoholes are numerically designed at SBAI Department, produced in collaboration with University of Padova (prof. G. Mattei and T. Cesca), and characterized in our laboratory. Characterization involves measurements different LCP and RCP extinction and absorption by means of transmission and photo-acoustic spectroscopy, with white light and laser sources. We characterize chiral substrates alone, chiral molecules on glass, and, finally, chiral molecules on chiral substrates, and monitor the change in enantioselectivity. The ultimate goal of the research is to use these low-cost substrates as chiral detectors able to distinguish low concentrations of both enantiomers.