SERS detection of benzophenones on viologen functionalized Ag nanoparticles: application to breakfast cereals

Silver (Ag) nanoparticles, as colloid suspensions or immobilized on an Ag plate, have been functionalized with the molecular assembler bis-acridinium dication lucigenin (LG) and have been used as a chemical sensor system to detect benzophenone (BP) and 4-methylbenzophenone (4MBP). The analytes strongly interact via their CO group with the N+–CH3 moiety of LG. Quantitative detection of BP and 4MBP had been obtained via a linear calibration curve by plotting the analyte concentration as a function of the intensity of the surface-enhanced Raman scattering (SERS) signals. Therefore, the method has been applied to detect BP and 4MBP extracted from spiked cereal samples. In fact, these molecules are commonly used in the area of food packaging, and, due to their volatility, can migrate through the packaging into the food. The lowest amount of analytes revealed by the SERS method, in the analyte stock solutions and in the spiked breakfast cereal, was at trace level, 50mM (9 ppm) and 70mM(25 ppm), respectively. The calculated limit of detection value was 16mM (3ppm). The measurements were compared to the results of conventional gas chromatography-tandem mass spectrometry (GC-MS/MS) spectrometry of the BP concentrations in the spiked breakfast cereals. For a BP (or 4MBP) concentration above 70mM (25ppm), there was a very good agreement between the SERS sensor and the GCMS/ MS determinations. In addition, no spurious bands due to other compounds present in the extract have been observed in the SERS spectra, indicating a good selectivity and specificity of the method. Thus, the SERS sensor can be applied, e.g. as a non-quantitative alarm sensor for relatively high benzophenone concentrations in breakfast cereals.