Boosting electromagnetic enhancement for detection of non-adsorbing analytes on semiconductor SERS substrates

The bigger pictureSERS is an ultra-sensitive sensing technique that has many important applications. For semiconductor-based SERS, the current consensus is that enhancement of analyte signals arises mainly from chemical interactions between analytes and semiconductors. As a result, semiconductor-based SERS has been limited to studying chemically adsorbing analytes, which are typically dyes and thiols. Herein, a MOF-coating strategy is developed in which the electromagnetic enhancing capability of ZnO nanoparticles is significantly boosted to enable the detection of non-adsorbing analytes, which is exemplified using VOC molecules. Given that MOF coating is a generally applicable strategy during material synthesis, the current work is expected to have a more profound impact on the development of semiconductor-based SERS for a wider variety of potential applications.Highlights•SERS detection of non-adsorbing VOC molecules is enabled on ZnO nanoparticles•VOC signals are enhanced through electromagnetic enhancement mechanism•Calculation shows that the field enhancement region is extended by ZIF-8 shells•The MOF-coating strategy paves the way for many semiconductor-based SERS applicationsSummarySurface-enhanced Raman spectroscopy (SERS) is a powerful technique that has found applications in many research fields. As promising alternatives to the current most popular plasmonic metal SERS substrates, semiconductor SERS substrates have many appealing attributes. However, they permit signal enhancement only to analytes adsorbed chemically on their surface, which means that semiconductor-based SERS can only be used for studying model analytes such as dyes or thiols. Using volatile organic compounds (VOCs) as an example, we demonstrate for the first time the detection of non-adsorbing analytes on ZnO nanoparticles. Specifically, this was achieved by coating ZnO nanoparticles with ZIF-8 shells, which enriches VOC molecules and dampens the decay of the electromagnetic field around their surface, thereby significantly boosting their electromagnetic enhancing capability such that it permits signal enhancement for non-adsorbing analytes. Importantly, the MOF-coating strategy is universal, which means that it may enable the detection of a wider variety of non-adsorbing analytes where conventional semiconductor-based SERS fails.Graphical abstract