Addressing the challenging stabilization of colloidal silver suspensions as an optimization tool for efficient Surface Enhanced Raman Scattering

Surface-enhanced Raman Scattering (SERS) is a highly sensitive technique for detecting trace amounts of analytes, widely used in diagnostics, environmental monitoring and chemical analysis. A key challenge when using nanocolloidal SERS substrates is the induced aggregation of plasmonic nanoparticles (NPs), necessary for "hot-spot" formation, which conventionally causes a sharp maximization of SERS scattering. Unfortunately, these aggregates are unstable in the solution, as they tend to grow until they eventually precipitate, followed by a consequent rapid decrease of the SERS signal. Current stabilizers, such as surfactants, polymers and inorganic compounds, focus on NPs stability rather than preserving the SERS signal for specific analytes, highlighting the need for improved stabilization strategies. This work explores the ability of a cationic surfactant, the hexadecyltrimethylammonium bromide (CTAB), as a delaying factor for the decay of the SERS signal of a representative analyte (methylene blue, MB), while promoting optimal "hot-spot" formation. In addition, an ionic liquid, the imidazolium chloride, is investigated as a dual action agent that causes aggregation retardation as well as stabilization of the SERS signal. • Aggregation of plasmonic NPs leads to unstable "hot-spot" formation. • CTAB delays the decay of the SERS signal, promoting stable "hot-spot" • CTAB preserves MB SERS signals for 1440 min vs. 30 min without CTAB • Imidazolium both retards aggregation and stabilizes SERS signal for up 7 days