CHEMICAL SCIENCE

Low-concentration SERS detection of non-adsorbed molecules based on electromagnetic enhancement


On February 20, 2023, the research team of Professor Jinlong Zhang and Professor Xiaoming Cao of East China University of Science and Technology published a study entitled “Boosting electromagnetic enhancement for detection of non-adsorbing analytes on semiconductor SERS substrates” in the journal Chem.

Based on surface-enhanced Raman spectroscopy (SERS), this study achieves low-concentration SERS detection of non-adsorbent molecules by coating metal-organic framework materials on the surface of semiconductor nanoparticles. In addition, through theoretical calculations, this study also proves that the electromagnetic enhancement mechanism is the main reason for enhancing the SERS signal of non-adsorbed molecules. The results of this study are expected to further promote the application of SERS technology based on semiconductor materials.

The corresponding authors of the paper are Ye Ziwei, Cao Xiaoming and Zhang Jinlong, and the first authors are Liu Xinyu, Ye Ziwei and Qianqiang.

Surface-enhanced Raman spectroscopy (SERS) has ultra-high detection sensitivity and is used in many research areas. The development of low-cost, high-activity SERS substrates is a research hotspot in this field. At present, the most common SERS substrate is the precious metal SERS substrate. The precious metal SERS substrate mainly enhances the SERS signal of the analyte molecule through the electromagnetic enhancement mechanism, which usually has extremely high detection sensitivity, but its disadvantages are active chemical properties, cumbersome preparation, and high price. In contrast, semiconductor SERS substrates have the advantages of stable chemical properties, convenient preparation and low cost. However, the vast majority of semiconductor SERS substrates can only enhance the SERS signal of analyte molecules through chemical enhancement mechanisms, which require analyte chemoadsorption on the semiconductor surface. Therefore, the traditional semiconductor SERS technology can only be used to study a very small number of chemically adsorbed molecules, such as dye molecules, thiol molecules, etc., which greatly limits the application prospects of semiconductor SERS technology. Recently, it has been reported that semiconductor SERS substrates such as Ta2O5, ZnO and SnO2-NiOx can also enhance the SERS signal of analyte molecules through electromagnetic enhancement mechanisms. Unlike chemical enhancement, electromagnetic enhancement can act on adsorbent/non-adsorbent analyte molecules within a certain range of the SERS substrate surface. However, compared with the precious metal SERS substrate, the electromagnetic enhancement ability of the semiconductor SERS substrate is extremely weak. Therefore, improving the electromagnetic enhancement ability of semiconductor SERS substrate is the key to expanding the application prospect of semiconductor SERS technology.

In this work, the research team of Professor Zhang Jinlong of East China University of Science and Technology designed and prepared ZnO nanoparticles with secondary structure, which improved the electromagnetic enhancement ability of ZnO nanoparticles by coating the outer surface with ZIF-8 shell, and realized the low concentration detection of six non-adsorbent volatile organic compounds (VOCs), and the detection limit can be comparable to that of precious metal SERS substrate. It is found that coating the surface of ZnO nanoparticles with ZIF-8 shell can not only enrich a large number of VOC molecules, but also change the refractive index on the surface of ZnO, thereby effectively inhibiting the attenuation of the electromagnetic field generated by Mie scattering on the surface of ZnO nanoparticles. This further expands the scope of electromagnetic enhancement mechanism on the surface of ZnO nanoparticles, so that the SERS signal of VOC molecules enriched in the ZIF-8 shell is electromagnetically enhanced, so as to achieve low-concentration detection of VOC molecules. In addition, density functional theory (DFT) calculations also show that coating the surface of ZnO nanoparticles with ZIF-8 shell can hinder the formation of chemical bonds between VOC molecules and ZnO through steric hindrance effect, avoid possible charge transfer between VOC molecules and ZnO, and thus exclude the influence of chemical enhancement mechanism. Therefore, the electromagnetic enhancement mechanism is the only mechanism of action in which the SERS signal of VOC molecules is enhanced.

Figure 1: Characterization of ZnO@ZIF-8 nanoparticles

Figure 2: SERS detection of pNTP by ZnO@ZIF-8 nanoparticles as SERS substrates

Figure 3: ZnO@ZIF-8 nanoparticles are used as SERS substrates to detect different VOC molecules

Figure 4: Electromagnetic field distribution on the surface of ZnO and ZnO@ZIF-8 nanoparticles

In summary, the results show that the electromagnetic enhancement ability of semiconductor SERS substrates can be significantly improved by coating MOF materials, which is of great significance for the design and application of semiconductor SERS substrates in the future. (Source: Science Network)

Related paper information:https://doi.org/10.1016/j.chempr.2023.01.017



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