Metal-organic frameworks: For functional surface enhancement Raman scattering

Abstract

Surface enhanced Raman scattering has been applied in many fields such as biology, food, environmental analysis owing to its high-sensitivity reading “fingerprint” characteristics in the collected Raman spectra, and provide important information for structure characterization, material interaction and chemical reaction mechanism. SERS have many advantages like highly sensitive, accurate, fast and noninvasive, while substrate material is one of the key factors to improve the performance of SERS. However, due to the difficulty of substrate preparation, time-consuming operation, and poor repeatability, new technologies are urgently developed to break through the bottleneck. Metal organic framework is a new porous material with the characteristics of ultra-high porosity, maximum specific surface area, diversified structure and easy functionalization, etc. In recent years, people have applied it to surface enhanced Raman scattering spectroscopy to detect trace compounds. In this paper, different methods of MOF for SERS substrate preparation and different fields of SERS detection are introduced. Combining MOF and SERS techniques provides a new direction for testing methods and material applications. Reasonable design and preparation of MOF body can precisely control the structure of the substrate, so as to optimize the substrate performance, such as adsorption performance, signal strength, stability, reproducibility and biocompatibility. In addition, this method provides a simple and powerful way to manufacture alternative substrates, which will stimulate innovative applications in the field of traditional technical methods and materials. We first introduced the preparation of different MOF substrates of SERS, including solo MOF as a SERS substrate, fixing nanoparticles on the surface of MOF, embedding metal nanoparticles inside MOF, core-shell structure based on MOF and MOF for integrating functional units as Reinforcement substrate. We also summarized the synthesis strategy and enhancement effect of MOF for SERS substrate. The most attractive feature of MOF is to obtain the required space structure by changing metal ions and ligands, which provides a novel synthesis method of SERS substrate. The research focus in this field is to select metal ions, connected ligands, spatial structures, porosity, coating form and measurement process optimization formed by combining metal ions and ligands. The complexity of samples measured in different research fields are different, and the requirements for substance of SERS are becoming more and more diverse, which brings us many challenges. Ultra-sensitive and highly reproducible detection of target analytes is especially important for scientific technology and methods or for practical applications. In the second section, we introduced the current application progress of MOF materials in SERS detection. By changing porous structures of MOF, the molecules to be tested can be separated and enriched, and the detection sensitivity can be improved. Detectable state of the test object of SERS extends from solid liquid to gas. Finally, we discussed the existing problems in the application of MOF in SERS and the future development prospects. Some special MOF has special conductivity, high charge mobility, and can be combined with current carbon materials, these MOF have been applied in energy storage and conversion, photoelectric catalysis, chemiluminescence etc. in which SERS are commonly applied for the characterization. No double the combination of SERS and MOF may provide potential to further explain the mechanism of the chemical reaction process in those areas. With the development of novel simple preparation methods of MOF and further research on materials, MOF will play a vital role in SERS analysis.