Excellence in Research: Investigation of Enhancer-Free Photogenerated Singlet Oxygen

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This project aims to study the role of light in the excitation of oxygen molecules. Excited molecules of oxygen, formally called singlet oxygen, play a crucial role in the fundamental mechanisms of cell life and death. New promising methods for cancer treatment and advanced techniques to sanitize food and pharmaceuticals use singlet oxygen generation to eliminate viruses, bacteria, and other microorganisms. Normally, mediator molecules, called photosensitizers, enable the shift of energy from the incident light to nearby oxygen molecules. This project studies the mechanisms of production of singlet oxygen in a water environment without the use of photosensitizers. If successful, the method will find widespread applications in environmental sciences, food safety, bio-pharmaceuticals, and medicine by providing an understanding of how microbe-inactivating, light-generated singlet oxygen is produced by sunlight and by providing an efficient and low-cost photosensitizer-free method to inactivate pathogens within foods, bio- and pharmaceutical products. The effort is a collaboration between scientists of Delaware State University, United States Department of Agriculture, Agriculture Research Service (USDA ARS) Food Safety and Intervention Technologies Research Units, and the Center for Advanced Studies in Photonics Research (CASPR) of the University of Maryland, Baltimore County (UMBC). The project involves Delaware State University, a Historically Black university (HBCU). The PIs incorporate diversity and broaden participation by attracting underrepresented students in STEM. This study seeks to confirm and characterize singlet oxygen enhancer-free production in water and to subsequently investigate the physical-chemical mechanisms of its creation, considering a direct one-photon absorption of visible light or through an indirect two-photon Raman process with the generation of a detectable Stokes-shifted photon. The study also investigates the role of the virus in the production of singlet oxygen molecules. Use of lasers to study the conversion of dissolved oxygen to reactive oxygen species in solution has not been previously undertaken. Continuous wave and pulsed laser sources in the blue region of the spectrum will be used to conduct direct and indirect Raman-based detection of singlet oxygen in water-settings. The research should provide new insights and ideas for detection and identification of singlet oxygen and will perhaps lay the pathway for an active and controllable production of the molecule. Successful completion of this research project would result in novel findings with potential applications for chemical-free sanitization of food, and bioproducts, as well as for disease treatments. Preliminary evidence shows that photosensitizer-free non-thermal generation of singlet oxygen by blue laser light is responsible for a significant reduction of virus activity. The study will expand the initial results and set the best set of conditions for an efficient singlet oxygen generation by using only light.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.