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

Surface-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.