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Plug-in Highly-sensitive pH Sensor Based on Polyacrylic Acid-chitosan Sensitive Film Coated Optical Fiber

In this paper, we developed a plug-in highly sensitive optical fiber Surface Plasma Resonance (SPR) pH sensor by coating polyacrylic acid - chitosan sensitive film on the sensing probe. Polyacrylic acid - chitosan sensitive film can sensitively sense the change of the external solution pH, and convert this change into its own expansion or contraction effect, thus changing its own refractive index (RI). Therefore, the optical fiber SPR sensor coated with the sensitive film can perceive the pH of the external liquid sensitively by tracking the movement of the resonance dip. The sensor is capable of indicating pH changes over a wide range from 4 to 9, and at higher pH regions (pH 8–9), the sensor can achieve an ultra-high sensitivity of 51.79 nm/pH. In addition, the sensor behaves good repeatability, stability and weak temperature cross effects, which is of great significance for the high-precision pH detection in many fields.