Monitoring the pH Value of an Aqueous Micellar Solution in Real-Time Using a Fiber Optofluidic Laser

Fiber optofluidic lasers (FOFLs) have attracted considerable research attention in the field of biochemical sensing due to their merits such as high sensitivity, low sample consumption, and real-time dynamic response. In this paper, we employ a Whispering Gallery Mode (WGM)-based FOFL to monitor the pH variation of rhodamine B (RB) aqueous micellar solution, in which small changes in pH are transformed into a dynamic response of the lasing spectral information in real-time, with a sensitivity of up to 7.3 nm/pH in the spectral shift for the pH in the range of 4.56–6.50. The sensor possesses a rapid response, high repeatability, good photostability, excellent reversibility, and immunity to the interference from the pump light, which can be used for in situ and real-time measurements in a wide range of biochemical applications. Additionally, the distinct dependence of lasing emission of RB molecules bound to surfactant micelles on the pH of an aqueous solution opens the possibility of using RB as an interfacial acid-base indicator.