An ITO Coated Bent Optical Fiber Sensor for Real-Time Monitoring Fe(CN)₆ ³⁻ Redox Reaction on Electrode Surface

In this work, the authors integrated electrochemistry and optical fiber spectrometry into one single fiber opto-electrode in developing a new chemical sensor technique: electrochemistry-assisted optical fiber chemical sensor (ECA-OFCS). The ECA-OFCS transducer of this work is a bent optical fiber probe (BOFP) coated with an electrically conductive and optically transparent (EC/OT) indium/tin oxide (ITO) membrane. In such an ECA-OFCS, an electrical potential can be applied to the ITO membrane electrode to induce redox reactions. These reactions can be used to eliminate interference species from solution in the Nernst diffusion layer adjacent to EC/OT membrane, or to convert an optically not-sensitive analyte in the Nernst layer to an optically sensitive species which can be detected with OFCS. Optical fiber evanescent wave spectroscopy is an ideal technique to monitor the chemical composition in the Nernst layer of EC/OT electrode coated on the surface of an BOFP. The authors report in this paper the method for coating an ITO membrane on surface of a BOFP, and observing electrochemically driving Fe(CN) 6 3− redox reaction on ITO membrane surface using BOFP evanescent wave absorption spectrometry.