Zeolitic-Imidazolate Frameworks Enhanced Surface Plasmon Resonance Sensor for Organic Dyes Sensing

This work highlights the development of zeolitic-imidazolate frameworks 8 (ZIFs-8) to enhance surface plasmon resonance (SPR) sensor for methylene blue compound detection. ZIF-8 was synthesized via the solvothermal method. XRD results show the appearance of diffraction peaks at 2\theta = 7.4^{\circ } , 10.4°, 12.7°, and 18.0°, which are assigned to 011, 002, 112, 022, 013, and 222 lattice planes, respectively, confirming the high crystalline ZIF-8 produced. The X-ray photoelectron spectroscopy (XPS) analysis exhibits the presence of C, O, Zn, and N elements on the surface of the ZIF-8 structure. Methylene blue was detected through the donor-acceptor interaction of a lone pair of Zn atoms in ZIF-8 with methylene blue. These two materials can also interact through \pi - \pi interactions because both ZIF-8 and methylene blue possess aromatic rings in their structure. The FESEM characterization shows a uniform particle size produced on a surface of Au thin film in the 100-130-nm range. A good sensitivity of 1.3821° ppm ^{-{1}} with a detection and quantification limit of 0.92 and 2.79 ppm, respectively, was obtained for the SPR sensor using ZIF-8 as a sensing material at a low methylene blue concentration range in comparison to bare Au. Nonetheless, the steepness of the graph started to decline after 1 ppm methylene blue concentration due to the fully occupied active sites on the surface of ZIF-8. In the selectivity study, a prominent SPR shift was observed when ZIF-8 interacted with methylene blue, compared to other interferences, proving that ZIF-8 has a good selectivity toward methylene blue.