An electroactive fiber optic chip for spectroelectrochemical characterization of ultra-thin redox-active films

The first, fully integrated, planar fiber optic platform with spectroelectrochemical capabilities, termed the electroactive fiber optic chip (EA-FOC) is presented here. Spectroelectrochemical techniques provide complementary optical and electrochemical data which are important for applications ranging from thin film characterization to advanced sensor design. To create the EA-FOC a side-polished fiber optic is coated with a thin film of indium-tin oxide (ITO) as the working electrode and used to probe electrochemically-driven changes in absorbance for surface-confined redox species. A sensitivity enhancement of ∼40 times higher than a transmission measurement is demonstrated for this first-generation EA-FOC, using the methylene blue (MB) redox couple, cycling between the visibly colored, oxidized form of MB, and its leuco (transparent) reduced form. Additionally, the EA-FOC is used to probe the redox spectroelectrochemistry of an electrodeposited thin film, about 0.3% of a monolayer, of the conducting polymer poly(3,4- ethylenedioxythiophene) (PEDOT). Unlike other waveguide formats, the EA-FOC offers an ease of use due to its ability to simply couple to light sources and detectors through standard fiber connectors to create a sensitive planar waveguide spectroelectrochemical platform.