In Situ DNA Detection Using a Phase-Demodulated High-Order Intermodal Interferometer Based on an Exposed-Core Microstructure Fiber

In this article, we demonstrate a phase-demodulated high-order intermodal interference based on exposed-core microstructure fiber (ECF), and it is applied for low-concentration in situ deafness gene DNA detection. The simulation results show that the phase sensitivity of the high-order interference mode (LP01–LP $_{\text {21{a}}}{)}$ is about $6\times $ higher than that of the low-order (LP01–LP $_{\text {11{b}}}{)}$ , which is different from the traditional wavelength-coded demodulation method. Hybridization experiments of complementary and noncomplementary deafness gene DNA fragments were carried out, and the sensing system was obtained to screen for complementary gene fragments. DNA complementary fragments with concentrations as low as 1 nM can be detected with a corresponding phase variation of 7.394°. The limit of detection (LOD) is as low as 0.046 nM. The experiment and theoretical analyses prove that this fiber optic biosensor can obtain high sensitivity and signal-to-noise ratio with phase-demodulation high-order intermodal interference scheme, which provides an alternative for the subsequent studies of high-sensitivity and high-precision sensors.