Drop‐coating deposition Raman spectroscopy of porphyrins

We report an improvement of the Raman detection sensitivity of porphyrins by factor of 10⁵ using drop‐coating deposition Raman spectroscopy (DCDR). We were able to obtain Raman spectra from ~20 nM initial (deposited) concentrations of cationic and anionic porphyrin. This detection limit is comparable with or even better than that of surface‐enhanced Raman scattering spectroscopy using Ag nanoparticles. Moreover, DCDR spectrum of protoporphyrin IX, which is known as a marker in clinical diagnostics of cancer, was also obtained from 10 nM deposited concentration. To our knowledge, it is the first demonstration of the resonance DCDR spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd.