[3] [3] WU S, CHENG W, QIU Y, et al. Fiber optic pH sensor based on mode-filtered light detection[J]. Sensors and Actuators: B Chemical, 2010, 144(1): 255-259.

[4] [4] JIN W, WU L, SONG Y, et al. Continuous intra-arterial blood pH monitoring by a fiber-optic fluorosensor[J]. IEEE Transactions on Biomedical Engineering, 2011, 58(5): 1232-1238.

[5] [5] SHAO M, QIAO X, FU H, et al. High sensitivity refractive index sensing of Mach-Zehnder interferometer based on multimode fiber core sandwiched between two waist-enlarged fiber tapers [J]. Optics Communications, 2013, 311: 359-363.

[7] [7] JONES T P , COLDIRON S J , DENINGER W J, et al. A Field-Deployable Dual-Wavelength Fiber-Optic pH Sensor Instrument Based on Solid-State Optical and Electrical Components[J]. Applied Spectroscopy, 1991, 45(8): 1271-1277.

[9] [9] CORRES J M, MATIAS I R, DEL VILLAR I, et al. Design of pH sensors in long-period fiber gratings using polymeric nanocoatings[J]. Sensors Journal, IEEE, 2007, 7(3): 455-463.

[11] [11] BHARDWAJ V, PATHAK A K, SINGH V K. No-core fiber-based highly sensitive optical fiber pH sensor.[J]. Journal of Biomedical Optics, 2017, 22(5): 057001-1-057001-9.

[12] [12] RONG Q, QIAO X. High-Sensitive Fiber-Optic Refractometer Based on a Core-Diameter-Mismatch Mach-Zehnder Interferometer[J]. IEEE Sensors Journal, 2012, 28(18): 2501-2505.

[15] [15] GU B, YIN M, ZHANG A P, et al. Biocompatible Fiber-Optic pH Sensor Based on Optical Fiber Modal Interferometer Self-Assembled With Sodium Alginate/Polyethylenimine Coating[J]. Sensors Journal, IEEE, 2012, 12(5): 1477-1482.

[16] [16] AMINAH N S, LIANI P H, HIDAYAT R, et al. Fabrication and Characterization of Surface Plasmon Resonance Sensor with Tapered Optical Fiber Structure[J]. Materials Science Forum, 2017, 886: 86-90.

[19] [19] ISLAM S, BAKHTIAR H, BIDIN N, et al. Sol-gel based thermally stable mesoporous TiO2 nanomatrix for fiber optic pH sensing[J]. Journal of Sol-Gel Science and Technology, 2018, 86: 1-9.