Optical investigations of electrochemical processes using a long-period fiber grating functionalized by indium tin oxide

The growing needs for fast and reliable sensing devices stimulate development of new technological solutions. In this work a new multi-domain sensing method is demonstrated where optical sensing device has been applied to enhance amount of data received during electrochemical analysis. Thin, optically transparent, high-refractiveindex, and electrically conductive indium tin oxide (ITO) film was deposited using magnetron sputtering on the surface of the long-period gratings (LPG) induced in optical fiber. ITO serves as working electrode in electrochemical setup and as a coating that enhances sensitivity of a LPG to changes of external refractive index. All the measurements were conducted in a combined optical and electrochemical setup. Obtained results show capability of this approach for optical monitoring of both electrochemical processes and changes in optical properties at the ITO surface. The optical response of the sensor was strongly dependent on the voltage applied to the ITO-LPG working electrode and on composition of the electrolyte. Changes observed in optical spectra may be attributed to the alterations in optical properties of both ITO layer (refractive index changes) and electrolyte in the vicinity of electrode (double layer formation). The developed structures can be further used as a fiber-based sensors and biosensors with integrated opto-electrochemical readout.