TITLE: Detection of Medium-Sized Polycyclic Aromatic Hydrocarbons via Fluorescence Energy Transfer AUTHORS: Nicole Serio, Lindsey Prignano, Sean Peters, and Mindy Levine* AUTHOR AFFILIATION: *Department of Chemistry, University of Rhode Island, 51 Lower College Road, Kingston, RI 02881; mindy.levine@gmail.com; 401-874-4243. Reported herein is the use of proximity-induced non-covalent energy transfer for the detection of medium-sized polycyclic aromatic hydrocarbons (PAHs). This energy transfer occurs within the cavity of γ-cyclodextrin in various aqueous environments, including human plasma. Highly efficient energy transfer was observed, and the efficiency of the energy transfer is independent of the concentration of γ- cyclodextrin used, demonstrating the importance of hydrophobic binding in facilitating such energy transfer. Low limits of detection were also observed for many of the PAHs investigated, which is promising for the development of fluorescence-based detection schemes. INTRODUCTION The accurate, sensitive, and selective detection of polycyclic aromatic hydrocarbons (PAHs) remains a crucial research objective, as many of these compounds are known or suspected carcinogens, 1 environmental pollutants, 2 and endocrine disruptors. 3 They are known components of crude and processed oil, 4 and have been found in the blood 5 and breast milk 6 of populations living in oil spill affected areas, and in seafood from the Gulf of Mexico following the Deepwater Horizon oil spill. 7 Despite the widespread prevalence and known toxicity of these compounds, current detection methods often have significant limitations, including the requirement for tedious sample preparation prior to analysis, 8 or the inability to accurately distinguish structurally similar PAHs with widely disparate toxicities. 9 Previous research in our group introduced a fundamentally new approach for the detection of PAHs, that relies on using the PAHs as energy donors in combination with high quantum yield fluorophore acceptors including BODIPY (compound 10) and Rhodamine 6G (compound 11) (Figure 1). 10-14 Energy transfer from the PAH to the fluorophore occurs when both are bound in the cavity of commercially available, non-toxic γ-cyclodextrin, leading to a new, brightly fluorescent signal in the presence of the PAH of interest (Figure 2). This energy transfer based detection has been used in complex biological fluids 14 and with PAHs that have been extracted from crude oil samples. 13 Previous research in our group focused predominantly on lower molecular weight PAHs, including anthracene, pyrene, and benzo[a]pyrene, with exceptionally efficient energy transfer observed from pyrene 2 and benzo[a]pyrene 3 to BODIPY 10. While benzo[a]pyrene is highly toxic, 15 many of the lower molecular weight homologues (naphthalene, anthracene, and pyrene) have greatly reduced toxicities. 16 Higher molecular weight PAHs, including benz[ a]anthracene, benz[b]anthracene, benzo(b)fluoranthene, and chrysene (compounds 4-7), are significantly more toxic to a wide variety of organisms. 17,18 The detection of higher molecular weight PAHs via cyclodextrin-promoted energy transfer would have significant potential utility in PAH detection in complex environments and in environmental remediation efforts. Other known toxicants include heterocyclic aromatic compounds such as carbazole (compound 8) 19 and environmental toxicants such as p-cresol (compound 9), 20 and the ability to use cyclodextrin-based energy transfer for the detection of these classes of toxicants would provide significant operational advantages. Reported herein are the results of our efforts towards achieving these goals: detecting higher molecular weight PAHs, heteroaromatic toxicants, and low molecular weight environmental toxicants via cyclodextrin-promoted, non-covalent energy transfer. EXPERIMENTAL Materials and Methods All chemicals were obtained from Sigma Aldrich Chemical Company and were used as received. Compound 10 was synthesized following literature-reported procedures. 21 Human plasma was obtained