*2.5. Micro-Raman Spectroscopy*

The SERS measurements were performed at the University of Southampton, during a stage of MSZ at the School of Chemistry. A Renishaw 2000 Raman spectrometer was employed to carry out both Raman and SERS measurements. The excitation laser employed was a Renishaw 785 nm laser and a CCD detector. The maximum power of the laser is 100 mW, but lower powers were used during the data acquisition, typically 0.05% and 1% (0.05 and 1 mW) to avoid to damage the samples. The collection time was 10 s for one accumulation. The spectrometer was equipped with a Leica DMLM series microscope. In order to collect scattered light at the sample, a microscope objective with a 50× magnification was employed with a short working distance (0.37 mm—numerical aperture 0.75). Noise filters and background correction were used for clarity when necessary.
