method, [9] electrochemical method, [10] fluorescence spectrometry, [11] photothermal effect method, [12] anodic dissolution voltammetry, [13] and surface plasmon resonance method. [14] However, colorimetric and photothermal methods require a lot of chemical reagents such as Amino-Functionalized Au@G NPs and Chloroauric acid, [9,12] which can easily cause environmental pollution. Both the anodic dissolution voltammetry and surface plasmon resonance methods are expensive because they require the consumption of a certain number of precious metals such as gold. [13,14] Many other ways of fluorescence spectroscopy, photothermal effect, and anodic dissolution voltammetry are complex, longer consuming time, and inconvenient inspection. [11][12][13] Optic-fiber sensors can be made with large bandwidth, low cost, lightweight, anti-electromagnetic interference, chemical inertness, easy to realize multi-band, and remote real-time monitoring capability, which have been widely used for temperature, [15] humidity, [16] refractive index, [17] gas concentration, [18] breath detection [19] and metal ion detection. [20] So far, many fiber optic sensing techniques for detecting metal ions have been proposed, and the main detection methods are intensity detection, [15][16][17]21] plasma, [22] fluorescence effect, [23] and interference wavelength detection. [24] The main trends are the preparation of sensitizing coatings, the use of vernier effects, and the preparation of micron structures. [20] Many structures of optic fiber are suitable for metal ion detection such as Bragg grating, [24] D-shaped fiber, [25] tilted fiber Bragg grating [26] , and microfiber. [27] Among them, optic-microfibers offering the possibility of strong evanescent fields out of fiber cladding for high-sensitive measurement provide a new option to explore more efficient and economical ion concentration sensing applications.In this paper, we present a microfiber interferometer sensor based on a ternary one-piece sensitive film (PVA-APTES-ICA (PVA, Poly(vinyl alcohol); APTES, (3-Aminopropyl)triethoxysilane; ICA, Imidazole-2-carboxaldehyde)) for the detection of copper ion concentration. The sensing structure can effectively enhance the detection capability of copper ions with a sensitivity of up to 7.715 × 10 6 nm M −1 and the detection limit of 0.0576 ppm in the concentration range of 100 to 1000 nM. The sensor has insensitive to temperature with a sensitivity as low as −0.007 nm °C−1 , which can ignore the temperature cross-influence. The sensor simplifies the manufacturing process of traditional sensors. Stability and anti-interference experiments demonstrated the longterm stability and good specificity of the sensor, which has good application prospects.An optic-fiber sensor for detecting the concentration of trace copper ions is proposed using a ternary cross-linked sensitive film coated on the Mach-Zehnder microfiber interferometer surface. The microfiber has a huge evanescent field offering high sensitivity to the ambient refractive index. The chelation...
