*2.1. High Performance Liquid Chromatography (HPLC-DAD/HPLC-ESI-Q-ToF-MS)*

For HPLC-DAD analyses, a HPLC system 2089 quaternary gradient with a diode array spectrophotometric detector MD-2010 was used, equipped with an AS-950 autosampler (Jasco International Co., Tokyo, Japan). Injection volume was 20 μL. ChromNav software was used to carry out data acquisition and data analysis. The chromatographic separation was performed on an analytical reversed-phase column TC-C18 (2) (250 × 4.6 mm, 5 μm for samples S#27 and S#9 and 150 × 4.6 mm, 5 μm for samples S#11 and S#5) with a TC-C18 (2) pre-column (12.5 × 4.6 mm, 5 μm), both from Agilent Technologies (Palo Alto, Santa Clara, CA, USA). The eluents were A, trifluoroacetic acid (TFA 0.1% *v*/*v*) in bidistilled water, and B, trifluoroacetic acid (TFA 0.1% *v*/*v*) in HPLC-grade acetonitrile. The flow rate was 1.0 mL/min and the program was 15% B for 5 min, then to 50% B in 25 min, then to 70% B in 10 min, to 100% B in 1 min and then hold for 5 min; re-equilibration took 13 min. The separation took place at room temperature (25 ◦C). The detector operated with spectra acquisition in the range of 200–650 nm every 0.8 s with 4 nm resolution.

For HPLC-ESI-Q-ToF analyses, a HPLC 1200 Infinity coupled to a Jet Stream ESI-Q-ToF 6530 Infinity detector was used, equipped with an Agilent Infinity autosampler (Agilent Technologies, Palo Alto, Santa Clara, CA, USA). Injection volume was 4 μL for S#27 and 10 μL for S#9 and S#5. MassHunter® Workstation Software (B.04.00) was used to carry out mass spectrometer control, data acquisition and data analysis. The chromatographic separation was performed on an analytical reversed-phase column Poroshell 120 EC-C18 column (3.0 mm × 75 mm, 2.7 μm particle size) with a Zorbax Eclipse plus C-18 guard column (4.6 mm × 12.5 mm, 5 μm particle size), both from Agilent Technologies (Palo Alto, Santa Clara, CA, USA). The eluents were A, formic acid (FA 1% *v*/*v*) in LC-MS-grade water, and B, formic acid (FA 1% *v*/*v*) in LC-MS-grade acetonitrile. The flow rate was 0.4 mL/min and the program was 15% B for 2.6 min, then to 50% B in 13 min, to 70% B in 5.2 min, to 100% B in 0.5 min and then hold for 1 min; re-equilibration took 10 min. During the separation, the column was thermostated at 30 ◦C. The mass spectrometer operated in ESI ionization in negative mode and the working conditions were: drying gas (N2, purity > 98%) temperature 350 ◦C and 10 L/min flow; capillary voltage 4.5 KV; nebulizer gas pressure 35 psig; sheath gas temperature 375 ◦C and 11 L/min flow; and fragmentor voltage 175 V. High-resolution MS and MS/MS spectra (CID voltage 30 V) were acquired

in negative mode in the range 100–1000 m/z at a scan rate of 1.04 spectra/sec (N2, purity 99.999%). Auto-calibration was performed daily using Agilent tuning mix HP0321 (Agilent Technologies) prepared in acetonitrile.

All samples were treated with 200 μL of 0.1% Na2EDTAaq/DMF (1:1, *v*/*v*) and extracted at 60 ◦C for 60 min in an ultrasonic bath; the extract was filtered on PTFE (0.45 μm) prior to injection.

#### *2.2. Surface-Enhanced Raman Spectroscopy*

SERS measurements were carried out utilizing modified Lee and Meisel citratereduced silver colloids by the reduction of silver nitrate (Aldrich silver nitrate 99.9%) with sodium citrate (Aldrich sodium citrate dehydrate 99%) [20]. The colloid has a characteristic absorption maximum at 426 nm and FWHM of 110 nm, as measured with a Hewlett Packard 8453 photodiode array UV–Vis spectrometer (following a 1:9 dilution with ultrapure water to observe maximum absorbance within the instrumental range). SERS measurements were firstly carried out by adding a 5 μL drop of colloid aggregated with magnesium sulphate directly onto micro-samples. On drying, the same micro-samples were subsequently exposed to hydrofluoric acid vapors for 5 min in a closed Eppendorf, then dried and examined again with a 5 μL drop of aggregated colloid [18]. Spectra were recorded using a laboratory Jasco NRS#3100 spectrophotometer with an argon laser emitting at 514 nm (grating 1200 lines/mm), and spectra could be obtained between 2 and 10 min after addition of the colloid and remained constant in quality until the evaporation of the liquid. Data were collected over the range 150–1800 cm−<sup>1</sup> with exposure times from 1–7 s and 3–10 accumulations. Laser power was maintained between 0.6 and 2 mW with an overall spectral resolution of ~4 cm<sup>−</sup>1. Polystyrene was used for instrument calibration. Raw data are shown, free from any manipulation other than being overlaid in graphs for reasons of clarity.
