Raman spectra were acquired with a Horiba XploRA Plus confocal Raman micro-scope equipped with a 532 nm laser. For measurements in liquid, the SERS substrate were placed in a dedicated holder. A 2μL aliquot of the solution was deposited over the substrate and covered with a glass slide coverslip. All measurements were acquired using a 10x microscope (Olympus, 0.25 NA). All spectra presented herein are an average of 10 individual scans. A laser power of 0.35 mW and an integration time of 10s were used. Smoothing and baseline correction were undertaken with Labspec 6 software.