Unsensitive-bending Mach-Zehnder interferometer for the detection of the Clostridium alpha toxin

An unsensitive-bending Mach-Zehnder interferometer (MZI) structure is proposed to detect the Clostridium alpha toxin by using single-mode fiber dislocation fusion. A standard single-mode fiber (SMF) is offset laterally and spliced between two SMFs to form the U-shaped microcavity in the middle, which is used for sensing. The MZI structure is encapsulated with capillary tube and injected with pure water, and the temperature sensitivity is tested in the temperature range of 26–50 °C. The temperature sensitivity of MZI is 0.78nm/°C, which ensures its practicability in the environment of temperature fluctuation. The axial tension and radial strain of MZI structure are measured. The weight range of the load is 10 to 60g. The experimental results show that the sensitivity of axial tension is −30.43 nm/N and the sensitivity of radial pressure is only −1.54 nm/N. The sensitivity of axial tension is about 20 times of radial pressure sensitivity. In the subsequent sensing experiments, axial fixation is needed to ensure the stability of MZI, the effect of radial pressure can be ignored under certain circumstances. Finally, the bending insensitive interferometer is used to detect the Clostridium alpha toxin, The sensing properties of MZI structure at concentrations of 2⁰, 2–¹, 2–², 2–³ were studied. When the concentration is 2⁰, the peak wavelength shift of the transmission spectrum can reach to 4.25 nm. Therefore, the proposed unsensitive-bending sensor has the advantages of high refractive index sensitivity, small size and low cost, which has a good prospect in biosensor applications.