ABSTRACT
Dual-functionality Au-on-Ag nanostructures (AOA) were fabricated on a silicon substrate by first immobilizing citrate-reduced Ag nanoparticles (Ag NPs, â¼43 nm in diameter), followed by depositing â¼7 nm Au nanofilms (Au NFs) via thermal evaporation. Au NFs were introduced for their catalytic activity in concave-convex nano-configuration. Ag NPs underneath were used for their significant enhancement factor (EF) in surface-enhanced Raman scattering (SERS)-based measurements of analytes of interest. Rhodamine 6G (R6G) was utilized as the Raman-probe to evaluate the SERS sensitivity of AOA. The SERS EF of AOA is â¼37 times than that of Au NPs. Using reduction of 4-nitrothiophenol (4-NTP) by sodium borohydride (NaBH4) as a model reaction, we demonstrated the robust catalytic activity of AOA as well as its capacity to continuously monitor via SERS the disappearance of reactant 4-NTP, emergence and disappearance of intermediate 4,4'-DMAB, and the appearance of product 4-ATP throughout the reduction process in real-time andin situ.
ABSTRACT
Edible oil is an indispensable food in daily life but early detection of its lipid oxidation is difficult. Developing new, rapid and accurate screening technique is urgently needed for oil quality control. Here we developed a surface-enhanced Raman spectroscopy analyzer based on plasmonic metal liquid-like platform (PML-SERS), which could directly analyze the oil sample in ca. 3 min. This analyzer has the ability and sensitivity to identify fingerprint peak changes. Moreover, the relative Raman intensity, I1265/1436, has a good correlation with peroxide value (POV), which is used for quantitative detection. The fitting model combined with principal component analysis (PCA) realized rapid spectral recognition for determining POV in edible oil oxidation. The relative deviation between the POV measured by PML-SERS and the national standard method (NSM) was less than 10%. Our platform provided a practical solution for ultra-sensitive and fast analysis of POV in oil oxidation.
Subject(s)
Algorithms , Food Analysis/methods , Oils/chemistry , Peroxides/analysis , Spectrum Analysis, Raman , Food Contamination/analysis , Oxidation-Reduction , Peroxides/chemistry , Principal Component Analysis , SoftwareABSTRACT
Objective:To study the Raman spectrum and the surface enhanced Raman spectrum ( SERS) of cefalexin, cefadroxil and cephradine, and analyze the surface enhanced Raman spectrum of the three compounds under different pH conditions. Methods:The Raman spectrum and the surface enhanced Raman spectrum of the three compounds under different pH conditions were detected and measured by a portable Raman spectroscopy. Results: The results showed that the three compounds could exhibit characteristic peak information in the surface enhanced Raman spectroscopy corresponding to that in the normal Raman spectrum, and the pH values had certain impact on the surface enhanced Raman spectrum of the three substances. Conclusion: Both the Raman spectrum and the surface enhanced Raman spectrum of cefalexin, cefadroxil and cephradine reflect certain fingerprint characteristics, and it is feasible to use Raman scattering method to identify the three cephalosporins.
ABSTRACT
The surface-enhanced Raman scattering (SERS) spectrum of pyridine adsorbed on Ag20 cluster (pyridine-Ag20 ) at room temperature is calculated by performing ab initio molecular dynamics simulations in connection with a Fourier transform of the polarizability autocorrelation function to investigate the static chemical enhancement behind the SERS spectrum. The five enhanced vibrational modes of pyridine, namely, υ6a, υ1, υ12, υ9a, and υ8a, can be assigned and identified by using a new analytical scheme, namely, single-frequency-pass filter, which is based on a Fourier transform filtering technique. To understand the factors evoking the enhancement in the SERS spectrum, the dynamic properties of molecular structures and charges for both of the free pyridine and adsorbed pyridine are analyzed. The calculated results indicate that the vibrational amplitudes of adsorbed pyridine are enhanced due to both of the electron transfer from pyridine to Ag20 cluster and the softening of pyridine bond. In addition, the N-Ag stretching within pyridine-Ag20 will couple with these five vibrational modes of pyridine. Consequently, the electron transfer between pyridine and Ag20 cluster induced by different molecular vibrational modes prompts the redistribution of electron density of pyridine. These factors collectively cause the noticeable change in polarizability during molecular vibrations and hence result in the enhancement of Raman peaks.