Surface Enhanced Raman Spectroscopy Detection Of Polycyclic Aromatic Hydrocarbons Using Gold Nanoparticles Substrates

Polycyclic aromatic hydrocarbons(PAHs) is of a large class of harmful persistent organic pollutants. The traditional detection method have disadvantage such as pretreatment for a long time and not convenient for in situ detection,so it is not enough to meet the demand of current detection. New analysis techniques of surface enhanced Raman scattering(SERS) provides high sensitivity vibrational spectra for the detection, become the field of environmental analysis in new means of detection.It has a great application potential. In this paper, three kinds of SERS enhanced substrates were prepared, and naphthalene, phenanthrene and pyrene, pyrene and their mixtures were detected.Gold colloids were prepared by the chemical reduction of HAu Cl4 using sodium citrate. Gold colloids with different size, range from 15 nm to 150 nm were synthesized by changing the amount of sodium citrate. Using these gold colloids, and through 785 nm Raman spectroscopy detection system, the SERS spectra of 4-Mercaptobenzoic acid aqueous solutions were detected, the minimum concontration obtained were 10-8 mol/L. Though calculating the SERS enhancement factor(EF), the gold particle size is 41 nm or 72 nm,they characterstic peak intensity is more good, which is in good agreement with the EF results.Then, the 10-5mol/L of the pyrene was detected by 41 nm gold colloids, and the characteristic peaks were not obvious. By the method of centrifugal concentration, the concentration of gold nanoparticles was increased, and the SERS spectra of naphthalene, anthracene, phenanthrene and pyrene in different concentrations were detected, and the detection limit was reached to 10-7 mol/L. For the mixture, we can distinguish each PAH easily for their own characteristic peaks.There is a linear relationship between peak intensity and concentration, the linear regression correlation coefficients were all above 0.985.To raise detection sensitivity of PAHs. In this paper, different proportions of the gold colloids, methanol and detection mixed, then dry. The influence of heating time to SERS activity was studied, and the best time was scheduled for 30 min. The best gold nanoparticle size is 72 nm. The effect of p H value and chloride ion to the enhancement of PAHs were researched for the first time. PH value and Cl- ions can equally effective enhanced PAHs Raman signals, by comparing, the optimum condition is p H=12. The result illustrated OH- ion can promote the adsorption between PAHs molecules and nanoparticles better. The SERS spectra of pyrene aquous solutions were dentected by the optimum gold colloids, the minimum concentration obtained were 10-8 mol/L.In the frist method, to obtain better detection effect, need to purification and concentration gold colloids, which increase the complexity of the sysnthesis. Seconed method, the signal has been further enhanced, but the repeatability of the substrate is not good. Finally, this paper explores easy access of the frosted glass, sand paper, and PDMS as SERS structures, though 633 nm Raman spectroscopy detection system, detection the SERS background value and detection of pyrene.