Studies On The Detection Of Nitrofuran Antibiotics By Surface-enhanced Raman Scattering

Nitrofuran antibiotics containing furazolidon （N1）, furantoin （N2）, furazone （N3）, andfuraltadone （N4） are a group of broad-spectrum antibacterial and were widely used inveterinary drug and feedstuff. But they have been forbidden in most of the countries becauseof the toxicity, mutagenicity, and carcinogenicity. But in china the cases of illegally using canalways been exposured. The Surface-enhanced raman spectrum （SERS） is the special opticalphenomenon based on metal nanoparticals which can give us the fingerprint spectrum ofmolecules. SERS has been developed quickly in many kinds of scientific researches recentyears for the advantages of accuracy, high efficiency, undamage, and the low expend. Thisresearch was aimed at deveploping a new kind of method to detect the Nirtofuran antibioticsby SERS.First, Density functional theory calculations was conducted with Gaussian03at theB3LYP level using the6-31G（d） basis set to optimized the structure of Nitrofuran moleculesand to analysis the assignment of raman vibrations. These four molecules are similar instructure so their vibrations are very closed, and the main vibrations are mostly attributed tothe peaks at1602cm^-1as the in-plane symmetric vibration of C=N;1556cm^-1as theasymmetric stretch and stretch vibration of NO₂and ring;1484cm^-1as in-plane stretchvibratino of Furan ring,1326cm^-1as the stretch and wag vibration and of C-C, C-N and C-H,1220cm^-1as the asymmetric stretch of C-N-N.Second, we made Au colloid and Fe₃O₄@Ag nanoparticels as the SERS active substrate.Their morphology and size were changed to adjust the optical property and the experimentconditions were optimized. When the Au colloid was used as the active substrate, the bestsolvent was acetone, and the volume ratio of sample and Au colloid was1:2, and the pHshould adjust to3.0⁴.0. The limit of detection was5.0ppm but N3could not been detected.When the Fe₃O₄@Ag nanoparticels were used as the active substrate, the size of Ag shellshould be40nm, and the concentration of Fe₃O₄@Ag nanoparticels should been0.5mg/ml,and the excitation wavelength should been633nm. The limit of detection was0.1ppm.What’s more, we modified the Ag shell with L-Cys, and the better SERS spectrum of N3wasachieved. The accuracy, LOD and repeatability of the Au colliod and Fe₃O₄@Agnanoparticels were compared and the Fe₃O₄@Ag nanoparticels were choosen as the SERSactivity substrate at last.Finally, the food samples were deternimed by this method. Although the SERS spectrumof impurities were very strong, the main raman vibration of Nitrofuran antibiotics namelyFuran ring, C=N, and NO₂could been detected.