Integrated Mach-Zehnder Interferometer based on dual-microchannel capillary core fiber for simultaneous label-free BSA and temperature measurement.

A compact, highly integrated dual-microchannel Mach-Zehnder interferometer (MZI) sensor based on an offset-core capillary-core fiber (CCF) is proposed for label-free and simultaneous detection of bovine serum albumin (BSA) concentration and temperature. Symmetrical C-shaped micropores are fabricated on both sides of the capillary air hole in the CCF via femtosecond laser micromachining, allowing the filling of thermo-sensitive materials to construct the temperature-sensing channel. Meanwhile, a C-shaped microcavity is inscribed at the offset fiber core to form the label-free BSA concentration-sensing channel. This design spatially isolates the temperature-sensing channel from the bio-sample microchannel, achieving two independent sensing paths. Experimental results show that the sensor delivers a temperature sensitivity of 8.884 nm/°C and a temperature resolution of 0.011 °C, and accurately monitors local temperature fluctuations during BSA detection within the concentration range of 20-60 mg/mL. This integrated fiber sensor exhibits promising application potential in disease diagnosis, therapeutic efficacy monitoring, and precision medicine, with great significance for clinical translation and biomedical basic research.