Determination of pH with surface-enhanced raman fiber optic probes

Methyl red, cresol red, and 4-pyridinethiol were examined for their ability to determine the pH at a surface. Methyl red and cresol red were coupled to cystamine. This produced a disulfide derivatized indicator which formed robust monolayers on silver substrates. The spectroscopic technique used to examine these compounds was surface-enhanced Raman spectroscopy. We determined that all of these compounds possessed surface-enhanced Raman bands which were characteristic of the molecular structure associated with the indicator and its conjugate acid