In-Fiber Interferometers for Detecting Biofilms

Bacterial biofilms pose significant challenges in medical and industrial settings, creating an urgent need for reliable tools capable of early detection. In this work, we demonstrate a compact fiber optic sensor for real time monitoring of biofilm formation, based on an in-fiber Mach-Zehnder Interferometer. The device is cost effectively fabricated by using of commercial single mode fiber through a waist-enlarged or overlap splice, which function as a robust intermodal coupler for core and cladding modes. A reflective configuration is achieved by depositing a silver coat on the fiber tip. This configuration resulting in a simple, low cost, and miniaturized probe ideal for in vivo measurements. The sensor exhibits a sensitivity to the surrounding medium of approximately 160 nm/RIU in the range 1.33-1.42. To evaluate its performance, the sensor was employed to track the biofilm growth of Pseudomonas Alcaligenes over a period of about three days. Changes in the resonance wavelength provided a clear indication of biofilm accumulation on the fiber surface. Independent Atomic Force Microscopy measurement analysis verified the presence of biofilm layer and enabled estimation of its thickness, confirming the sensors utility as a practical tool.