Sensitivity improvement by Langmuir film formation on a spectroelectrochemical fiber-optic sensor surface†

This study introduces a method for enhancing spectroelectrochemical sensor sensitivity by incorporating optical fiber technology. The sensor comprises a gold mesh electrode coated on the surface of an exposed optical fiber core. Total reflection attenuation spectroscopy was employed to measure the optical properties of the fiber core surface. To enhance sensitivity, we investigated surfactant addition to the sample, anticipating the formation of an electrostatic film on the optical fiber core surface. Spectroscopic measurements were conducted on 24 dyes, including cationic methylene blue and anionic indigosulfonic acid, as target substances. Consequently, adding surfactant at approximately one-tenth of the critical micelle concentration slightly improved the measurement sensitivity for cationic dyes, with a 2.3-fold increase observed for methylene blue. Previously challenging anionic dyes were successfully detected using this method. In addition, this technique was successfully applied to sulfide ion determination using the absorbance spectrophotometric method with methylene blue. The findings indicated that this approach markedly enhances the sensitivity and adaptability of spectroelectrochemical sensors using fiber optic, particularly in the detection of a wide variety of chemical substances.