(766d) Oscillatory Surface Reactions of Riboflavin, Trolox and Reactive Oxygen On Single-Walled Carbon Nanotubes Probed by near Infrared Fluorescence

Semiconducting single-walled carbon nanotubes (SWNTs) fluoresce in the near-infrared and are promising as optical sensors when suitably functionalized to enable selective analyte recognition.  Their detection limit has been extended down to the single molecule, as the SWNT emission can stochastically fluctuate in a quantized manner in response to single-molecule adsorption and desorption events. In this study, we identify for the first time, the signature of the complex decomposition and reaction pathways of Riboflavin using isolated SWNT sensors dispersed onto an  aminopropyltriethoxysilane (APTES) coated glass slide.  The SWNT emission is quenched by Riboflavin and singlet oxygen, but increased by Trolox, which functions as a reductive brightening agent.  Because Riboflavin oxidizes the Trolox and is also a photosensitizer for singlet oxygen and superoxide generation, the disparity in the reaction rates for each of these reactions creates an oscillatory fluorescence response from each isolated SWNT or bundle on the surface.  This oscillatory behavior allows for the simultaneous detection of multiple species for a reactive system using SWNT emission. A series-parallel kinetic model is shown to describe the critical points of these oscillations, with predicted partition coefficients on the order of 10^-5.