In-fiber optofluidic michelson interferometer for detecting small volume and low concentration chemicals with a fiber ring cavity laser

An in-fiber optofluidic Michelson interferometer fabricated by femtosecond laser micromachining technology was presented. The interferometer structure was prepared by a special optical fiber with two cores and a microchannel . One core was connected to the core of a single-mode fiber (SMF) and functioned as a sensing arm on the microchannel inner wall, the other core worked as a reference arm and was connected to the optical waveguide introduced by femtosecond laser processing. By combining with a ring cavity laser, the detection limit (DL) of the interferometer could be improved. The laser sensor presented a high linear response with a refractive index (RI) sensitivity of 1039.77 nm/RIU and the calculated DL could reach as low as 1.675 × 10 −5 RIU. Then, the sensor measured different concentrations of vitamin C in tablets in the concentration range of 0–10 mg/mL with a detection limit of 0.06 mg/mL. Due to the advantages of optofluidic structure, the volume of the detection solution could be as low as few tens of nanoliters, and the time to replace and detect the solution only took a few seconds. In addition, the laser sensor realized label-free DNA hybridization detection through surface functionalization , and could detect 1 μM target DNA solution with high specificity. This sensing device had great potential for small volume and low concentration sample detection in the biochemical field.