[1] Kingsy Grace R, Manju S. A comprehensive review of wireless sensor networks based air pollution monitoring systems[J]. Wireless Personal Communications, 108, 2499-2515(2019).

[2] Zhang J T, Zhu Z J, Chen C M et al. ZnO-carbon nanofibers for stable, high response, and selective H2S sensors[J]. Nanotechnology, 29, 275501(2018).

[3] Ali F I M, Awwad F, Greish Y E et al. Hydrogen sulfide (H2S) gas sensor: a review[J]. IEEE Sensors Journal, 19, 2394-2407(2019).

[4] Wu L Q, Song H J, Lü Y. Recent advances in gas sensors for hydrogen sulfide[J]. Journal of Instrumental Analysis, 37, 1192-1198(2018).

[5] Huang B, Chen Y C, Guo Z J et al. A new sensitive fluorescent H2S probe based on Cu 2+ complex[J]. Chinese Journal of Inorganic Chemistry, 29, 2283-2288(2013).

[6] Chen K, Yuan S, Gong Z F et al. Ultra-high sensitive photoacoustic spectrometer for trace gas detection based on fiber-optic acoustic sensors[J]. Acta Optica Sinica, 38, 0328015(2018).

[7] Chen K, Yuan S, Gong Z F et al. High sensitive detection for SF6 decomposition component of H2S based on laser photoacoustic spectroscopy[J]. Chinese Journal of Lasers, 45, 0911012(2018).

[8] Wu H P, Dong L, Zheng H D et al. Enhanced near-infrared QEPAS sensor for sub-ppm level H2S detection by means of a fiber amplified 1582 nm DFB laser[J]. Sensors and Actuators B: Chemical, 221, 666-672(2015).

[9] Chen K, Zhang B, Liu S et al. Parts-per-billion-level detection of hydrogen sulfide based on near-infrared all-optical photoacoustic spectroscopy[J]. Sensors and Actuators B: Chemical, 283, 1-5(2019). http://www.sciencedirect.com/science/article/pii/S0925400518321191

[10] Liu M, Feng D J, Feng W L. Properties of hydrogen sulfide gas sensor based on no-core-multimode-no-core fiber structure[J]. Acta Optica Sinica, 39, 1006007(2019).

[11] Wang Y Y, Dai Z Y, Tang D L. Development status of optical hydrogen sulfide gas sensor[J]. Sensor World, 22, 13-17(2016).

[12] Liu T, Wang W Q, Liu Z Q et al. Optical fiber sensor for mercury ion detection based on quantum dots and evanescent wave sensing[J]. Acta Optica Sinica, 38, 1006008(2018).

[13] Shen T, Feng Y, Dai H L et al. Measurement of magnetic field based on optical fiber evanescent wave sensor[J]. Acta Optica Sinica, 35, s106003(2015).

[14] Itoh K, Madou M. Optical waveguides for surface spectroscopy: FePO4 thin-film/K +-doped glass composite optical waveguide systems having tapered velocity couplers[J]. Journal of Applied Physics, 69, 7425-7429(1991).

[15] Yimit A, Itoh K, Murabayashi M. Detection of ammonia in the ppt range based on a composite optical waveguide pH sensor[J]. Sensors and Actuators B: Chemical, 88, 239-245(2003).

[16] Yimit A, Rossberg A G, Amemiya T et al. Thin film composite optical waveguides for sensor applications: a review[J]. Talanta, 65, 1102-1109(2005). http://www.ncbi.nlm.nih.gov/pubmed/18969919

[17] Tuerdi G, Nizamidin P, Kari N et al. Optochemical properties of gas-phase protonated tetraphenylporphyrin investigated using an optical waveguide NH3 sensor[J]. RSC Advances, 8, 5614-5621(2018).

[18] Patima N, Abliz Y, Kiminori I. Synthesis and optical-electrochemical gas sensing applications of Ni-doped LiFePO4 nano-particles[J]. New Journal of Chemistry, 40, 295-301(2016).

[19] Abudukeremu H, Kari N, Zhang Y et al. Highly sensitive free-base-porphyrin-based thin-film optical waveguide sensor for detection of low concentration NO2 gas at ambient temperature[J]. Journal of Materials Science, 53, 10822-10834(2018).

[20] Abdukader A, Shawket A, Abliz Y. High sensitive optical waveguide sensor for detection of H2S gas[J]. Chinese Journal of Sensors and Actuators, 20, 1937-1939(2007).

[21] Maimaiti A, Abdurahman R, Kari N et al. Highly sensitive optical waveguide sensor for SO2 and H2S detection in the parts-per-trillion regime using tetraaminophenyl porphyrin[J]. Journal of Modern Optics, 67, 507-514(2020).

[22] Noman M T, Ashraf M A, Ali A. Synthesis and applications of nano-TiO2: a review[J]. Environmental Science and Pollution Research, 26, 3262-3291(2019). http://link.springer.com/10.1007/s11356-018-3884-z

[23] Chen X M, Qing D K, Itoh K et al. A TiO2 film/K + ion-exchanged glass composite optical waveguide and its application to a refractive index sensor[J]. Optical Review, 3, 351-355(1996).

[24] Kari N, Wang L, Nizamidin P et al. Planar optical waveguide-based dimethylamine sensor with cresol red/TiO2 composite thin film[J]. Journal of the Optical Society of America B:Optical Physics, 37, 601-607(2020).

[25] Yang H Q, Qi Z M. Optical waveguide ammonia sensor[J]. Optics & Optoelectronic Technology, 9, 16-19(2011).

[26] Kluson P, Drobek M, Kalaji A et al. Preparation, chemical modification and absorption properties of various phthalocyanines[J]. Research on Chemical Intermediates, 35, 103-116(2009).

[27] Zuo X, Wei Y D, Wu Y Q. High sensitive and selective gas sensing materials: metallophthalocyanines[J]. Progress in Chemistry, 16, 68-76(2004).

[28] Kumar A, Joshi N, Samanta S et al. Room temperature detection of H2S by flexible gold-cobalt phthalocyanine heterojunction thin films[J]. Sensors and Actuators B: Chemical, 206, 653-662(2015).

[29] Song Z Q, Liu G M, Tang Q X et al. Controllable gas selectivity at room temperature based on Ph5T2-modified CuPc nanowire field-effect transistors[J]. Organic Electronics, 48, 68-76(2017).

[30] Wu H, Chen Z M, Zhang J L et al. Stably dispersed carbon nanotubes covalently bonded to phthalocyanine cobalt(II) for ppb-level H2S sensing at room temperature[J]. Journal of Materials Chemistry, 4, 1096-1104(2016).

[31] Yang C X, Huang H, Huang T et al. Preparation and superhydrophilic mechanism of porous TiO2/SiO2 composite thin film[J]. Applied Chemical Industry, 42, 1174-1179(2013).

[32] Sayyara K, Tajigul E, Mariya M et al[J]. Preparation of nitrogen dioxide optical waveguide gas sensitive element and its gas sensing properties Instrument Technique and Sensor, 2018, 23-27.

[33] Yang L R, Liu Z G, Zhang L et al. Preparation and photocatalytic activity of monodisperse mesoporous TiO2 microspheres by sol-gel method[J]. Journal of the Chinese Ceramic Society, 44, 75-80(2016).