A new approach to measure melamine, cyanuric acid, and melamine cyanurate using surface enhanced Raman spectroscopy coupled with gold nanosubstrates

Abstract

Vibrational spectroscopic characteristics of melamine, cyanuric acid, and melamine cyanurate were measured using surface-enhanced Raman spectroscopy (SERS) coupled with gold nanosubstrates. Trace amounts of melamine and its analogues (cyanuric acid and melamine cyanurate) were characterized and quantified quickly and accurately by SERS in combination with partial least squares (PLS) analysis. Based on the relationship between the Raman intensity of the most prominent peak at around 676 cm -1 and log values of melamine concentrations, the limit of detection (LOD) of SERS for melamine was estimated to be 2.6 9 10 -7 mol L -1 (*33 ppb). An approximately 3 9 10 4 fold of enhancement factor for SERS signals of melamine on gold nanosubstrates was obtained. This result was based upon the comparison of the peak at around 676 cm -1 in the SERS spectra with that of normal Raman spectra of melamine in aqueous solutions. SERS spectra of cyanuric acid acquired from its solid form differ significantly from this compound in an aqueous solution, indicating a possible keto-enol isomerization reaction of cyanuric acid in water. When equal amounts of melamine and cyanuric acid were added together, spokelike crystals of melamine cyanurate formed instantly, which could be measured and characterized by SERS. This study demonstrates that SERS could provide a fast and ultra-sensitive tool for detection and characterization of melamine and its derivative compounds in aqueous solutions.

Determination of chloramphenicol and crystal violet with surface enhanced Raman spectroscopy

“…The active surface of Klarite ( Fig. 2) has regular arrays of inverted square pyramid subunits which are about 1 lm deep and 1.8 lm long, while the distance between each subunit is about 0.4 lm [15]. The active surface of Q-SERS is much more irregular than that of Klarite, containing gold particles of about 40-60 nm in diameter distributed on the surface of a glass slide as shown in Fig.…”

Application of surface enhanced Raman spectroscopy for analyses of restricted sulfa drugs

“…The gold coated active surface of Klarite has regular arrays of inverted square pyramid subunits (deep: 1 lm; length: 1.8 lm; distance between subunits: 0.4 lm), which was fabricated by nanoscale lithographic patterning technique [17]. The Klarite has shown potential in detection of trace amounts of melamine, cyanuric acid and melamine cyanurate as well as Bacillus spores [18,19]. SERS spectra of a tested solution were recorded after the solvent of the solution (1.0 lL) deposited on the active area of Klarite TM being evaporated.…”

A review of traditional and novel detection techniques for melamine and its analogues in foods and animal feed

“…With the aid of gold-or silver-based nanostructures, Raman signals can be enhanced more than 1 million times due to spatially localized surface plasmon resonance (SPR) from the "hot-spots" where huge local enhancements of electromagnetic field are obtained [18]. As a result, the sensitivity of SERS could reach ppb or to a single molecule level [19], making SERS much more sensitive than conventional Raman spectroscopy [8]. SERS could provide highly specific information about chemical and biochemical species with "fingerprint-like" signatures for identification of samples.…”

“…Ideal characteristics of analytical techniques for melamine detection include the following: (1) high sensitivity or low limit of detection (LOD); (2) high specificity; (3) short detection time; (4) low cost; (5) portable; (6) minimum or no sample preparation; and (7) suitable for measuring melamine in a variety of complex food matrixes [8][9][10][11]. Unfortunately, no existing method meets all the aforementioned requirements.…”