A Colorimetric Multifunctional Sensing Method for Structural‐Durability‐Health Monitoring Systems

A colorimetric multifunctional phototransmittance‐based structural durability monitoring system is developed. The system consists of an array with four indium gallium zinc oxide (IGZO)‐based phototransistors, a light source at a wavelength of 405 nm through a side‐emitting optical fiber, and pH‐ and Cl‐selective color‐variable membranes. Under illumination at the wavelength of 405 nm at corrosion status, the pH‐ and Cl‐responsive membrane, showing a change in their color, generates a change in the intensity of the transmitted light, which is received by the phototransistor array in the form of an electrical current. I_ds and R (I_ds/I_{pH 12}) are inversely proportional to the pH, which ranges from 10 to 12. When the pH drops from 12 to 10, the magnitude of I_ds and R increases to ≈10³. In the case of Cl detection, I_ds and R (I_ds/I_{Cl 0 wt%}) increase nearly 50 times with an increase in Cl concentration of 0.05 wt%, and when the Cl concentration reaches 0.30 wt%, I_ds and R increase to ≈10³ times greater. This multifunctional colorimetric durability sensing system demonstrates considerable potential as a novel smart‐diagnostic tool of structural durability with high stability, high sensitivity, and multifunction.