Smartphone-Based Hand-Held Optical Fiber Fluorescence Sensor for On-Site pH Detection

In order to realize remote and on-site pH detection, we design a simple, economical, and hand-held optical fiber pH sensor based on smartphone platforms. All components of the sensor are encapsulated in a 3-D printed shell, including a semiconductor laser for exciting fluorescence signal, a smartphone with a filter for collecting fluorescence signal, a fiber coupler for transmitting light, and batteries for laser power supply. With the combination tapered fiber probe modified with CdSe/ZnS quantum dots, whose fluorescence signal can be captured by the smartphone camera and calculated by a self-developed Android application, the sensor has a minimum sensitivity of 0.5-pH unit and a wide detection range between pH 4 and 12. Moreover, the sensor shows good reusability and stability. Considering its low cost, miniaturization, portability and the capability for remote detection, real-time monitoring, and on-site analysis, the proposed smartphone-based optical fiber pH sensor has great application potential in environmental monitoring and biomedicine.