| Summary: | <p> The optimal surface enhanced Raman scattering (SERS) intensity was correlated to the localized surface plasmon resonance (LSPR) of individual and aggregated gold core/silver shell (<i>Au@Ag</i>) nanoparticles (NPs) in titrations involving the addition of both SERS label (e.g., rhodamine 6G, R6G) and the non-SERS active aggregant (chemical species that triggers the aggregation of NPs) potassium chloride (KCl). Titrating NP solutions with pure SERS label has often resulted in highly non-linear calibrations. In some cases, addition of non-SERS active aggregating agents such as KCl has also resulted in a large increase in SERS signals. An order of initial addition was followed in this report to find any advantage from the initial addition between the SERS label or the aggregant KCl. Interactions between <i>Au@Ag</i> solution and the SERS labels of R6G, 4 mercaptopyridine (MPY) and 4 mercaptobenzoic acid (MBA) were followed using spectrophotometric titrations. Evaluations of the role of aggregation in NP solutions were conducted through the micro-titrations using a quartz cuvette and in two separate stages: (1) a single amount of KCl was followed by increasing amounts of SERS label, and (2) a single amount of SERS label was followed by increasing amounts of KCl. The present reports allowed to conclude that the graphs of SERS intensity (λ<sub> EX</sub> = 785nm, corrected for solution absorption) versus aggregate absorptions (λ<sub>AG</sub> = 830 nm) had a correlation between intense SERS and LSPR band extinctions.</p>
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