Fabrication of the Optical Fiber pH Sensor Based on CdSe/ZnS Quantum Dot

During the past decade, there has been a lot of research on the application of quantum dots (QDs) in photonics and biotechnology. QDs are semiconductor nanocrystals which show many peculiar optical and electrical properties due to their quantum confinement effects. In this work, the correlation of the fluorescence intensity of QDs and the pH under ambient temperature was studied. An optical fiber pH sensor was prepared using CdSe/ZnS carboxyl quantum dots as sensing media. QDs with different sizes and emission colors (green, yellow, and red) were immobilized on the surface of the optical fiber through EDC/sulfo-NHS coupling reaction. The optical fiber was immersed in water, and the photoluminescence (PL) spectra of QDs were obtained at ambient temperature under various pH conditions. The photoluminescence (PL) intensity of QDs increased linearly with the increase of pH, and among the QDs, the red emitting QDs show the largest change in PL intensity with pH. This shows that QDs can be used as pH sensing media and optical fiber pH probe can be prepared.