Research bottlenecks in SERS
Research bottlenecks in SERS research
Underlying mechanism not fully understoodAs our understanding of the mechanism of the SERS effect is not complete, it is hard to optimize the SERS technology. Different morphologies of the nanoparticles on a surface can enhance different molecules and therefore standardization of a SERS substrate product can be difficult (1).
Maintaining reproducibilityMetal nanoparticles tend to agglomerate, because of their high surface energy. The smaller the size of particle the higher the interfacial area which will mean an increase in the potential for aggregation by electrostatic and van der Waals forces (2). When great agglomerates arise, the nanomaterial layer will not have a homogeneous spread of nanoparticles providing equal enhanced signals and thus equal Raman measurements at all locations of the SERS substrate. The measurements become more reliable when the reproducibility of the SERS substrates increases. Also, it could be possible that the nanoparticles on a surface tend to blend with the analyte instead of staying attached to the surface where they should enhance the analyte.
Shelf life of substratesCorrosion products can arise when the metallic nanomaterial reacts with its environment and this could minimize the SERS effect. Therefore, SERS substrates have a shelf life, in which they work well and after that period of time the SERS effect minimizes. Chemical mono-layers could be used as corrosion barrier (3), but then again it can decrease the SERS effect of the nanoparticles as it creates a distance between the nanoparticles and analyte.
1) Panneerselvam et al: Surface-enhanced Raman spectroscopy: bottlenecks and future directions. Chemical Communications 2018.
2) Jiang et al: Characterization of size, sruface charge, and agglomeration state of nanoparticle dispersions for toxicological studies. Journal of Nanoparticle Research 2008.
3) Liu et al: Compact Shielding of Graphene Monolayer Leads to Extraordinary SERS-Active Substrate with Large-Area Uniformity and Long-Term Stability. Scientific Reports 2015.