7. Project Summary/Abstract While ethylene has long been known as an important plant hormone it has also been demonstrated to be produced in mammals as a result of oxidative stress that is hallmark to numerous diseases. In particular ethylene arises from the radical fragmentation of lipid peroxides and/or intermediates in their formation. The formation of lipid peroxides is a result of reactive oxygen species, which are implicated as playing stress or signaling roles in numerous diseases including cancer, cardiovascular disease, and neurodegenerative diseases amongst others. While there are some sophisticated spectroscopic methods for sensitively measuring the biomarker ethylene in exhaled breath, these approaches are necessarily limited in spatial resolution and complexity of sample. Recently, our group has developed a profluorescent chemodosimeter that is capable of detecting ethylene in live cells; however the current sensitivity is insufficient for detection of endogenous ethylene. Therefore the overall goal of this exploratory research proposal is to determine if structural and targeting modifications can provide the necessary sensitivity to study the endogenous production of ethylene and any potential signaling roles. To achieve this goal we aim to (1) structurally optimize the ligands about the ruthenium and tune the photophysical properties of the appended fluorophore; and (2) to use subcellular targeting of the probe to cellular domains where ethylene is expected to be present in higher concentrations. It is expected that the proposed research will result in probes with significantly improved limit of detection (~2 orders of magnitude) in the range that might be expected for endogenous ethylene levels in disease states. This will primarily be accomplished through synthesis of modified probes, characterization of resulting properties, and localization studies in live cells. This exploratory research is expected to evaluate the feasibility of detecting endogenous ethylene levels and lay the groundwork for further investigations into ethylene's production at the cellular level. The ability to detect ethylene with spatial resolution not available using current approaches would provide a broadly applicable tool capable of reporting lipid peroxidation. 1