Superchiral Light Generation on Achiral Substrates for High Sensitive Detection of Chiral Molecules

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Chirality is a ubiquitous property of life, found at many levels of biological systems from left-handed amino acids to right-handed glucose. It gives rise to the inherent chirality to DNAs, proteins and more, which remained hitherto unexplored due to the unavailability of precise characterization techniques. These chiral biomolecules can be present in both handed symmetries with undistinguishable physical properties, such as density, molecular weight or electronic and vibrational transitions frequencies making them almost impossible to differentiate with common spectroscopic techniques. Here a unique achiral plasmonic surface is proposed, which outperforms previous approaches. In the preliminary work chiral molecule detection sensitivity that is four orders of magnitude higher compared to the conventional technique, but without the extensive and tedious sample preparation and at much lower sample volume, is demonstrated. Pharmacological and toxicological characterization of chiral molecules plays a crucial role in the pharmaceutical drug industry and FDA approval process. The proposed project will also serve to train graduate students in nanolithography and device fabrication. Based on these attributes the proposed novel molecular chirality detection scheme has high potential to generate commercial interests and can become real world sensing technique in near future.Technical: The proposed unique cavity-coupled achiral plasmonic surface outperforms previous approaches in the following aspects: It does not have geometrical chirality, hence no chiral signal from the substrate; It creates strong near-fields on the upper surface exposed to the target analyte; The near-field is 100% single-handed chiral and flip handedness depending only on the excitation handedness on the same substrate. Such a unique mechanism of superchiral near-field generation is possible due to the coherent interaction between degenerate plasmonic and photonic cavity modes. These attributes are exclusive compared to any previous attempts where inhomogeneous chiral near-field and structural CD diminishes chiral signal from molecules. In the preliminary studies, chiral light-matter interaction through surface enhanced vibrational circular dichroism with about four orders of magnitude enhancement in detection sensitivity compared to conventional volumetric CD (VCD) technique is demonstrated. The proposed system will permit efficient chiral-light matter interactions for the detection of vibrational molecular chirality in the MIR domain relevant for drug screening. Unlike previous demonstrations where two independent chiral substrates with opposite handedness were needed, the proposed work promises chiral near-field interaction on a single achiral plasmonic substrate paving the path towards surface enhanced chiroptical spectroscopy.The main focus of the project will be to develop a sensitive chiral compound identification technique using our achiral plasmonic substrates. The system will be benchmarked with pharmacologically significant chiral drug compounds like Ibuprofen, Thalidomide, propranolol, Albuterol, and Isoflurane. These chiral compounds will allow us to start the characterization of the system and will further expand. The pharmacological and toxicological characterization of enantiomers plays a crucial role in the pharmaceutical drug industry and FDA approval process. Therefore, there is still an active need for efficient enantiomer detection, precisely and cheaply. We strongly believe that the proposed research will allow us to overcome some of the previous challenges and enable us to develop a low cost, high throughput, high sensitive chiral molecule detection technique.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.