ABSTRACT
Robust pH sensors were created by using the pH-dependent surface enhanced Raman scattering (SERS) of mercaptobenzoic acid (MBA) isomers on gold-silica nanoshell (NS) lms. All isomers are bound to the NS through the thiol moiety producing nanoscale pH sensors. Using the ratio between the Raman signals f rom c arboxylic a cid (COOH, 1712 cm−1) a nd t he c arboxylate (COO−, 1416 cm−1) g roups, t he pKa’s of 2-, 3-, and 4-MBA on NS w ere found to b e between 7.2 and 7.4. In addition, the out-of-plane stretching mode (1568 cm−1) of 3-MBA was found to have a linear response to the local pH and could be used to monitor pH between 5 and 11. To investigate multifunctional sensing, a mixed monolayer system comprised of cysteine-polyethylene glycol (PEG)- uorescein (Cys-PEG-Fl) and 4-MBA was created and characterized with Raman and uorescence spectroscopies.
