Figure 5: LIQUISOR detection of Lysozyme.

(a) Solution phase Raman spectrum of Lys in PBS at concentrations of 1 mM (red line) and 10 mM (black line). Integration times are 30 s (10 mM) and 300 s (1 mM). The two spectra have been shifted for clarity and normalized to the integration time, so the intensities are directly comparable. The zoom in the 1000 cm⁻¹ region of the 10 mM spectrum (b) highlights the presence of the Phe-Trp doublet peaked at 1008 cm⁻¹ and 1015 cm⁻¹, together with the intense PBS signal at 983 cm⁻¹ Only the PBS contribution is visible at 1 mM spectrum (c). SERS spectra of Lys at concentrations of 100 nM (d, blue line and zoom in e) and 1 μM acquired on an early stage aggregate, after few minutes irradiation (d, black line and zoom in f), and after 60 min irradiation (d, red line and zoom in g). A tentative modes assignment (details in Supplementary Table S4) is carried out based on the Raman modes measured on the powder and in liquid at 10 mM (Supplementary Fig. S11). The SERS spectra were acquired with integration times of 60 s (1 μM early stage and 100 nM) and 40 s (1 μM). The spectra shown in the figures are rescaled to the same integration time, so to be directly comparable, and offset for clarity. In the zooms displayed in (b,c,e–g) the symbols refer to the experimental data which are fitted with a multi-peaks Lorentian model (black, red and blue lines) to extract the position of the single peaks of PBS, Phe and Tyr (green lines). Experiments are carried out with laser wavelength 632.8 nm, laser power 6.7 mW, microscope objective 100X.