Detection of Nitrate and Sulfate Anions by Normal Raman Spectroscopy and SERS of Cationic-Coated, Silver Substrates

Abstract

The use of normal Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) of cationic-coated, silver substrates to detect nitrate and sulfate ions in aqueous environments is examined. For normal Raman spectroscopy using near-infrared excitation, a linear concentration response was observed with detection limits of 260 and 440 ppm for nitrate and sulfate, respectively. Detection limits in the low parts-per-million concentration range for these anions are achieved by using cationic-coated, silver SERS substrates. Adsorption of the anions on the cationic-coated SERS substrates is described by a Frumkin isotherm.

Surface-enhanced Raman scattering of sulfate ion based on Ag/Si nanostructure

“…When the sodium sulfate solution was diluted to 1 Â 10 -10 mol/L, there is only one Raman peak at 996 cm -1 . Therefore, the detecting limit of sulfate is determined as 1 Â 10 -9 mol/L, which is much lower than the reported value of 4.6 Â 10 -3 mol/L [25].…”

Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles

“…However, the sulfate band is not present in the SERS spectrum of the mixed solution. Since the sulfate band will in principle be enhanced when the sulfate is adsorbed to the SERS substrate [65,129] these measurements allow us to conclude that hardly any of the sulfate present in the solution is adsorbed onto the surface of the silver NPs, while the citrate layer remains on the surface showing little alterations. These measurements suggest that the direct interaction of the ion with the NP surface does not lead to the observed increase in the agglomeration rate with increasing salt concentrations.…”

“…Thus, the surface-enhanced Raman spectroscopy provides an ideal tool for the ultrasensitive technique detection of molecules exclusively on or nearby the surface of plasmonic nanostructures [36][37][38][39]64]. The detection of sulfate SERS signals has long been reported for silver substrates [65].…”

Intracellularly grown gold nanoislands as SERS substrates for monitoring chromate, sulfate and nitrate localization sites in remediating bacteria biofilms by Raman chemical imaging

“…Nitrate (green spectrum) and sulfate (blue spectrum) have Raman bands at 1061 cm −1 and 982 cm −1 , respectively. These bands are assigned to the symmetric stretching vibration modes, v 1, of these anions [35, 36]. Since sulfate is present as an electrolyte, several studies have reported its SERS spectrum and these were used as standards [54–56].…”

“…Surface enhanced Raman Spectroscopy (SERS) offers 10 7 –10 12 folds [30, 31] increase in signal enhancement and can be used to investigate vibrational properties of adsorbed molecules at very low concentrations [32, 33]. SERS has also been employed to enhance Raman signal of inorganic anions such as chromate [34], nitrate [35], sulfate [36], chlorate [37], and phosphates [38]. …”