In-situ DNA detection using a phase-demodulated high-order intermodal interferometer based on an exposed-core microstructure fiber

In this paper, 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 (LP 01 -LP 21a ) is about 6 times higher than that of the low-order (LP 01 -LP 11b ), which is different from the traditional wavelength coded demodulation method. Hybridization experiments of complementary and non-complementary 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 7.32 °. The limit of detection is as low as 0.089 nM. The experiment and theoretical analysis 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.