SERS Titration of 4-Mercaptopyridine Self-Assembled Monolayers at Aqueous Buffer/Gold Interfaces

Abstract

Determination of the surface pK(a) of self-assembled monolayers (SAMs) at aqueous buffer/gold interfaces using surface-enhanced Raman scattering (SERS) measurements, namely, SERS titration, is reported for the first time. From the analysis of pH-dependent SERS spectra of 4-mercaptopyridine monolayers on gold, the pK(1/2) (3.9 ± 0.2) was determined. By further correlating the surface pH value with the bulk pH value in terms of the Gouy-Chapmann model, the surface pK(a) (5.3 ± 0.3) was evaluated accordingly. Compared to the conventional contact angle titration, SERS titration has the advantage of giving further insight into the microscopic and dynamic information of the surface-confined functional groups. In addition, such a technique has high sensitivity, micrometer spatial resolution, and chemical selectivity.

Direct observation of surface‐enhanced Raman scattering in ZnO nanocrystals

“…6(a) and 6(b), a marked shift of the C-S stretching mode is exhibited at 727 cm −1 and an increase in intensity of the C-S stretching mode at 1119 cm −1 in comparison with the Raman spectrum of 4-Mpy solution. A similar shift and enhancement have previously been observed in the SERS spectra of 4-Mpy adsorbed on Au and Ag surfaces, [27] which was interpreted as the coordination of 4-Mpy with the metal surface through the sulfur atom. Therefore, we conclude that 4-Mpy is adsorbed on ZnO nanocrystals via the sulfur atom.…”

Enhanced Raman Scattering as a Probe for 4-Mercaptopyridine Surface-modified Copper Oxide Nanocrystals

“…A similar downward shift and enhancement have been observed for 4-Mpy adsorbed on other metal substrates such as Au 33 and Pt 34 surfaces. Both bands are so-called X-sensitive modes, 35 that can be described as strongly coupled substituent and aromatic ring modes.…”

Incorporation of the fluoride induced SiO bond cleavage and functionalized gold nanoparticle aggregation into one colorimetric probe for highly specific and sensitive detection of fluoride

“…In aqueous solution, the MPD-AuNPs aggregated quickly in the presence of F − through HB interaction, namely the terminal pyridine group of MPD formed N H F − HB, which resulted in the increase of the ratio of absorbance at 625 nm to that at 525 nm (A 625 /A 525 ) for the MPD-AuNPs. Since pyridine group must be protonated to form the N H F − HB, the solution pH would greatly influence the response of MPD-AuNPs to F − [53,54]. At pH ≥ 9.0 (Fig.…”