Development of optical fiber sensors for high-alkaline pH monitoring based on silica fluorescent nanoparticles

Fluorescent fiber optic sensors hold promise for monitoring the pH of concrete due to their high accuracy and small size, but they still face issues such as long response times and dye leaching. To address the issues, this study presents the fabrication of fluorescent nanoparticles by encapsulating pH-sensitive fluorescent dyes within nanoparticles to avoid the dye leaching. These fluorescent nanoparticles were then integrated into a PVA/SiO₂ sol–gel film matrix, forming a uniform film at the tip of a hydroxylated and silanized optical fiber using the dip coating method. Experimental results show that the response time of the fluorescent sensor was 40 s. The fluorescence intensity of the sensor decreased with increasing pH, exhibiting a proportional linear response in the pH range of 9 to 13. The sensor is minimally interfered by common ions in concrete, has a precision of ± 0.1 pH units, and demonstrates good accuracy in pH measurement of actual concrete pore solutions.