Fig. 3.

(a) SERS difference spectra of (black) 0, (red) 0.11, (blue) 0.33, (green) 3.3, and (orange) 13.6 μM uranyl. Experimental conditions: λ_ex = 785 nm, t_int = 30 s, P = 40 mW, 10 mM EPPS buffer, 0.7 nM carboxylated IE Ag@Au@SiO₂ nanoparticles. Samples were equilibrated for 30 min prior to analysis. (b) Correlated (1) uranyl (870–800 cm⁻¹) and (2) carboxylate (940–870 cm⁻¹) SERS signals (integrated areas). Black solid lines represent Langmuir adsorption isotherm analysis.