Methylene Blue Optical Fiber Sensor Filled with Calcium Alginate Hydrogel

As it is a typical dye pollutant in water, methylene blue detection is important to health and environmental safety. A kind of methylene blue optical fiber sensor was successfully fabricated, which was highly sensitive, responded linearly, was easy to manufacture and was low cost. The sensor was composed of a capillary glass tube, single-mode fiber and calcium alginate hydrogel. The interference spectrum of the optical fiber F–P cavity successfully responded to the methylene blue solution. The response sensitivity of 2.46 nm/(mg/L) was obtained with the typical sensor with a 39.18 μm cavity length. The linearity of the experiment curve was 0.99247. Furthermore, the influence of sodium alginate concentrations on sensitivity was also investigated. The results showed that the sodium alginate concentration had an optimum value. In addition, the dynamic response characteristic was tested. A 25 s response time was obtained with testing using a typical sensor, which showed a fast response time. The sensor has the potential to be applied to online methylene blue detection.