The motivation for this project is the need for a sensitive, stable means to monitor the concentration of dissolved oxygen.  Photodynamic therapy, the process through which singlet oxygen is generated by reaction of O₂ with a photosensitizer incorporated in a tumor, is now a widely practiced tumor treatment.  A critical limitation of this therapy is that tumor cells exhibit hypoxia, a deficiency of oxygen in the tumor tissue.  We plan to synthesize 15-100nm oxygen sensors that, due to their small size, can be incorporated into a tumor cell. Measurement of oxygen levels within the cells can be used in a feedback mode to determine appropriate levels of intracellular oxygen before turning on higher light fluxes to generate singlet oxygen to kill the cells.

       The goal of this project is to create a multifunctional sensor - one which can monitor oxygen concentration in small volumes (~1 μm³), as well as efficiently generate reactive singlet oxygen that can chemically modify the environment around the sensor.  Specifically, the basic unit of this sensor is nanocrystalline microporous material (zeolite-Y), which has interconnected supercages of ~13Å dimensions with 7Å windows.  A chromophore that absorbs visible light, tris-bipyridine ruthenium(II) (Ru(bpy)₃²⁺), will be synthesized within the supercages at high loading levels (~1 Ru complex per 10 zeolite cages).  Stern-Volmer plots will give insight as to the distribution of Ru complex in the zeolite.  In the presence of oxygen, the excited state of Ru(bpy)₃²⁺ is quenched, and monitoring either the emission or lifetime can provide a quantitative measure of the oxygen.  Upon quenching, the molecular O₂ is converted to singlet oxygen (¹O₂), which is a powerful oxidant able to alter its nearby environment.  The zeolite sensors will be tested in both normal and tumor cells via a confocal optical microscope.

Sensor Mechanism

Ruda, Toni A.  Dutta, Prabir K.  “Fenton Chemistry of Fe-III Exhanged Zeolitic Minerals Treated with Antioxidants.”  Environ. Sci. Technol.  2005, 39, 6147-6152.

Ruda, T.; “Optical Oxygen Sensor:  Oxygen Quenching of Ru(bpy)3+2 Entrapped in Siliceous Zeolite-Y” Annual IGERT Symposium, Columbus, OH. December, 2005.