A fluorescence-based imaging-fiber electrode chemical sensor for hydrogen peroxide

The fabrication and characterization of imaging fiber electrodes (IFEs) is presented, and the concept of an electrochemically-modulated, fluorescence-based, imaging-fiber electrode chemical sensor (IFECS) is demonstrated. In brief, an imaging fiber distal tip was sputter-coated with a semi-transparent gold layer to create an IFE, and a fluorescent redox dye was immobilized across the IFE face to create an IFECS. An electroactive analyte was imaged by monitoring the change in the immobilized redox dye's fluorescence following its homogeneous electron transfer reaction with the electroactive analyte. Fluorescence images were collected through the IFECS and detected by an epi-fluorescence microscope/CCD imaging system. Cyclic voltammetry and fluorescence microscopy were utilized to characterize the electrochemical and fluorescence properties of IFECSs. Reversible voltammetry was observed for the rhodamine B isothiocyanate (RBITC) redox couple at IFEs. IFECSs using RBITC as the fluorescent redox dye and Nafion as the immobilization polymer were fabricated to detect hydrogen peroxide. The IFECS's RBITC-fluorescence was decreased by ˜27% upon exposure to 250μM hydrogen peroxide and ˜95% of the original fluorescence was observed following the electrochemical regeneration of the Nafion-immobilized RBITC. These IFECSs represent the first union in which remote fluorescence imaging of an electroactive analyte can be performed through the actual fiber-optic electrode itself.