Surface-enhanced Raman Spectroscopy. For SERS measurements, substrates were immersed for one hour with a drop of aqueous solution of CV (1 µM) and then dried under compressed air. For Raman, a 15 µL drop of an aqueous solution of CV (0.1 M) was pipetted onto a glass substrate and another glass cover slide was pressed on top of it. SERS and Raman spectra were measured on an inverted microscope with a 60× air objective (NA = 0.85, CFI Plan Fluor, Nikon) using a 785 nm CW laser (LM-785-PLR-175, Ondax, Monrovia, CA) delivering 0.562 mW to the sample, respectively. The scattered light was filtered with either a 532 nm notch filter (NF533-17, Thorlabs, Newton, NJ) and passed through a 10 μm slit. This light was then reflected off of a 650 nm blaze, 1350 lines/mm grating (Richardson Gratings, Newport, Rochester, NY), in a spectrograph (Kymera 328i, Andor Technology, Belfast, U.K.) and detected using a back-illuminated CCD with a sensor temperature of -80˚C (Newton 970, Andor).