Modification of a SERS-active Ag surface to promote adsorption of charged analytes: effect of Cu²⁺ ions

This work studies the impact of electrostatic interaction between analyte molecules and silver nanoparticles (Ag NPs) on intensity surface-enhanced Raman scattering (SERS). For this, we fabricated nanostructured plasmonic films by immobilization Ag NPs glass plates functionalized them a set differently charged hydrophilic thiols (sodium 2-mercaptoethyl sulfonate, mercaptopropionic acid, 2-mercaptoethanol, 2-(dimethylamino)ethanethiol hydrochloride, thiocholine) to vary surface charge SERS substrate. We used two oppositely porphyrins, cationic copper(II) tetrakis(4- N -methylpyridyl) porphine (CuTMpyP4) anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine (CuTSPP4), with equal value similar structure as model analytes probe signal. Our results indicate that spectrum strongly, up complete signal disappearance, correlates substrate, which tends be negative. Using data obtained our system, analyzed modification different reagents (lithium chloride, polyethylenimine, polyhexamethylene guanidine, multicharged metal ions). Finally, all those modifications were tested using negatively oligonucleotide labeled Black Hole Quencher dye. Only addition copper ions into solution yielded good Considering strong molecules, suppose inversion played key role in this case, instead change substrate surface. Changing could promising way get clear spectra SERS-active supports.