Hydrogel Optical Fiber Based Ratiometric Fluorescence Sensor for Highly Sensitive Ph Detection

A type of flexible hydrogel optical fiber, which consisted of a permeable core/clad structure with a step-index profile for highly efficient excitation light guiding and fluorescence emission collecting, has been judiciously designed and fabricated. The effects of refractive index and core/clad diameter on propagation loss of hydrogel optical fiber have been examined and verified theoretically and experimentally. To demonstrate the feasibility of the designed optical fiber for fluorescence sensing, in a representative experiment two types of fluorescent materials serving as a pH probe and internal reference were integrated into the core of the designed hydrogel optical fiber to obtain a ratiometric pH sensor, which eliminated the disturbance of the external environment. The prepared fluorescent sensor displayed linear responses to pH values ranging from 3.79 to 9.55 with a high sensitivity of 0.68 per pH unit, indicating the great potential of the hydrogel fiber-based sensor for on-site, real-time, and highly sensitive detection of pH in aqueous environments.