Polymer-Integrated Optical Fiber Photothermal Fabry–Perot Interferometer for High Sensitivity Detection of β-Carotene

$\beta $
-carotene is an important precursor of vitamin A. Excessive consumption can cause carotenemia, which endangers human liver and kidney functions. Therefore, the detection of
$\beta $
-carotene is important for protecting human health. However, current detection methods are costly, time-consuming, and not suitable for online detection. In this study, an optical fiber Fabry–Perot interferometer (FPI) is proposed that contains a single-mode fiber (SMF), multimode fiber (MMF), and polydimethylsiloxane (PDMS). The PDMS not only acts as a cavity but also as a sensing unit. Because PDMS has a large coefficient of thermal expansion, it responds well to photothermal signals. The analyte
$\beta $
-carotene produces a photothermal effect (PTE) under laser irradiation at 480 nm, which can change the transport characteristics of the FPI. The experimental results show that the sensitivity reaches 50 pm/(mg/L) with a limit of detection (LOD) of 0.4 mg/L, which is lower than that of the conventional liquid chromatography method. This sensor has a simple structure, high sensitivity, high mechanical strength, and good stability; therefore, it has potential applications in food safety and environmental pollution detection.