Figure 2

Normal Raman spectrum of Xylenol Orange (C_XO = 600 µM, 420 mW excitation power, 20 s acquisition) (a) and SERS spectra of spermine cross-linked aggregates of Ag NPs with (b) or without entrapped XO molecules (C_XO = 1.5 or 0 µM, 290 mW excitation, 7 s acquisition) (c).