Polyacrylamide/2-Thiophenecarboxaldehyde Hydrogel Functionalized Fiber Optic Mercury Ion Trace Detection

Mercury is a toxic heavy metal that can easily cause serious harm to human health and the environment. To quickly and sensitively measure the concentration of mercury ions (Hg2+), a fiber optic sensor based on polyacrylamide/2-thiophenecarboxaldehyde (PAM-TH)-functionalized Mach–Zehnder interferometer (MZI) is proposed and demonstrated experimentally. The prepared modified polyacrylamide and 2-Thiophenecarboxaldehyde are combined by Schiff base reaction to form a 3-D network hydrogel with specific binding properties for Hg2+. The ultrasensitive Hg2+ detection is realized by coating hydrogel on the surface of highly sensitive MZI based on polarization maintaining photonic crystal fiber (PMPCF). The experimental results verify a limit of detection of approximately 0.87 fM, which is two orders better than that of the reported fiber-based Hg2+ sensors. Through the desorption of mercury ions in the sensor film by ethylenediaminetetraacetic acid (EDTA), the proposed sensor demonstrates good reusability under a wide dynamic detection range from 0.01 pM to 10 nM.