An in-fiber sensor for simultaneous measurement of cholesterol concentration and temperature based on SPR and MMI.

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are −0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C–46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field. An optical fiber sensor with SPR + MMI double effect superimposed is fabricated by collapse-welding method. The AuNPs/β-CD composite is synthesized by reduction method and connected to the sensing region by covalent bond to identify cholesterol molecules. In addition, hollow fiber filled with glycerin is an excellent temperature-sensitive material that can be used for temperature sensing. Based on the above design, cholesterol concentration and temperature can be measured simultaneously by demodulation of mixed sensing signals. [Display omitted] • An MMF–HCF–MMF fiber structure was proposed for simultaneously exciting SPR and MZI. • A composite material of AuNPs/β-CD was utilized for highly sensitive measurement of cholesterol concentration. • The glycerol was filled into the HCF for highly sensitive measurement of temperature. • The proposed sensor possesses high sensitivity, excellent stability and selectivity. [ABSTRACT FROM AUTHOR]