Abstract
Target molecules adsorbed onto metallic nanoparticles can have their Raman and/or fluorescence signals enhanced, leading to the called surface-enhanced [resonance] Raman scattering (SE[R]RS) or surface-enhanced fluorescence (SEF). Here we have applied Au nanorods (AuNRs) coated with a surfactant bilayer leading to a positive surface charge to investigate the role played by these AuNRs in colloidal suspension on SERRS and SEF effects of charged molecules. In the case of the anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc), besides achieving SERRS with an enhancement factor (EF) of ca. 105, the AuNRs allowed the analytical application of the SERRS effect for the NiTsPc between 8.3x10-6 and 4.0x10-5 mol L-1. The limit of detection of 4.8x10-7 mol L-1 (at 752 cm-1) and 1.3x10-6 mol L-1 (at 1338 cm-1) was found. In the case of the cationic methylene blue, the SEF effect was achieved reaching an EF of ca. 10. Besides, fundamental discussions are carried out considering the results presented here.
Highlights
The inelastic light scattering represented by the Raman scattering spectroscopy has a low cross-section, which is a limitation of the technique when applied in the analysis of ultrathin films or highly diluted solutions (
The anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc) molecules, which are preferentially arranged as aggregates in aqueous solution, are physisorbed preferentially as monomer onto Au nanorods (AuNRs), perpendicularly oriented, and driven by electrostatic interactions between sulfonated SO3- (NiTsPc) and quaternary ammonium N+ (CTAB) groups
The AuNRs allow the analytical application of the surface-enhanced resonance Raman scattering (SERRS) effect for NiTsPc reaching a minimum limit of detection (LOD) of 4.8x10-7 mol L-1 for the band at 752 cm-1
Summary
The inelastic light scattering represented by the Raman scattering spectroscopy has a low cross-section (ca. 10-29 cm2/molecule), which is a limitation of the technique when applied in the analysis of ultrathin films (monolayers or a few nanometers of thickness) or highly diluted solutions (
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