Study On Novel Chemical Sensors Based On Surface-Enhanced Raman Spectroscopy

Surface enhanced Raman spectroscopy（SERS）has emerged as one of the most promising analytical tools in recent years.Because the methods has some advantageous,such as sensitivity,specificity,ease of operation and rapidity,it is particularly suitable for food and environmental analysis.Therefore,the preparing sensitive and selective substrates have received sufficient the attention of researchers who were interested in using SERS sensor for quantitative measurements.In the thesis,we successfully developed several SERS-based sensors for determination of organic small molecules and inorganic ions in food and water samples.This thesis included the following parts:1.SERS sensor for determination of melamine in milk products.We have synthesized silver nanoparticles（Ag NPs）decorated with α-cyclodextrin（CD）by using the traditional silver mirror reaction in the presence of CD.The CD-Ag NPs were used as SERS substrate for determining melamine.The intensity of the Raman band of melamine at 704 cm^-1 was used to determine melamine in milk and milk powder.The use of CD-Ag NPs as the SERS substrate rather than classical silver nanoparticles makes the method more sensitive in giving an enhancement by a factor of upto ¹06.The effects of the volume of solutions（of CD-Ag NPs,Na Cl,Na OH,melamine）and mixing time were investigated.The standard addition method was employed for quantitative analysis.The correlation coefficient of the calibration plot is 0.9995,and the limit of detection is 3.0 μg L^-1.The method was successfully applied to the determination of melamine in milk and milk powder,with relative standard deviations of <10 % and recoveries between 89 and 104 %.2.SERS sensor for determination of Hg²⁺ in environment waters.We have developed a SERS probe for the determination of Hg²⁺ using methimazole-functionalized and CD-Ag NPs.These Ag NPs in p H 10 solution containing sodium chloride exhibit signal SERS at 502 cm^-1.Its intensity considerably decreases in the presence of Hg²⁺.This effect serves as the basis for a new method for the rapid,fast and selective determination of trace Hg²⁺.The linear range is from 0.50 μg L^-1 to 150 μg L^-1,and the limit of detection is 0.10 μg L^-1.The effect of 11 metal ions commonly encountered in environmental water samples was found to be negligible.The method was applied to the determination of Hg²⁺ in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and relative standard deviations of <3.5%（n=5）.3.SERS sensor for selective determination of o-phenylenediamine in environment waters.We have developed a SERS sensor for the determination of o-phenylenediamine（OPD）in water.It is based on the chemical cyclization reaction of OPD with nitrite in acidic medium.Benzotriazole（BTAH）,one of the products of the reaction,can be determined by SERS with high sensitivity using CD-Ag NPs as SERS substrate.The acidity of the medium,nitrite concentration,reaction time and mixing time for solution of analytes and SERS substrate were optimized.The analytical range is from 0.10 to 1.0 μmol L^-1,the limit of detection is 30 nmol L^-1,and the limit of quantification is 100 nmol L^-1.The high selectivity for OPD was confirmed by studies on the potentially interfering species m-and p-phenylenediamine,aniline,and 1-naphthylamine.Recoveries of OPD from spiked real water samples ranged from 97.8 to 104.5 %,with relative standard deviations of less than 4 %.4.SERS sensor for ultrasensitive determination of formaldehyde based on derivatization reaction.A selective and ultrasensitive SERS sensor was developed for the determination of formaldehyde（HCHO）in environmental waters and food samples.It is based on derivatization of 4-amino-5-hydrazino-3-mercapto^-1,2,4-triazole（AHMT）with HCHO.One of the products of the derivative reaction,6-mercapto-5-triazolo[4,3-b]-s-tetrazine（MTT）,can be quantified by SERS at 832 cm^-1 using Ag NPs as substrates.The incubation time for derivatization,the volume of reagents and the mixing time were optimized.The peak areas of the signal are linearly related to the concentration of HCHO in the 1^-1000 μg L^-1 range,the limit of detection is 0.15 μg L^-1,and the limit of quantification is 0.45 μg L^-1.Recoveries obtained by analyzing two spiked samples of environmental water and two spiked food samples were in the range between 64.0 and 111.1 %.There is no significant difference between the results obtained by the present method and the liquid chromatographic method（Chinese industrial standard method,SN/T 1547-2011）.5.SERS sensor for determination of Hg²⁺ based on rhodamine-bonded and amino group functionalized Si O₂-coated Au–Ag core–shell nanorods.We designed a new type of SERS sensor with high selectivity and sensitivity for the determination of Hg²⁺ at picomolar concentrations based on hydrolysis reactions.The Rhodamine 6G-derived Schiff base bonded and amino group functionalized Si O₂-coated Au–Ag core–shell nanorods（Au@Ag@Si O₂–NH₂-R6 G,NR-Rs）,which show extraordinary enhancement factor（EF）and good stability,were employed as the SERS substrate of the sensor.The tunable ability of the chemical bonding of the substrate generates appropriate probe molecules bound to the surface of the nanorods（NRs）and improves the selectivity and sensitivity of the SERS sensor dramatically.The limit of detection（LOD）of Hg²⁺ obtained with the present SERS sensor was 0.33 pmol L^-1.Furthermore,the proposed substrate has p H-responsive ability.The present sensor is suitable for the on-site determination of p H and Hg²⁺ by combining with a portable Raman spectrometer.6.A fluorescence and SRES dual-signal sensor for p H based on Rhodamine derivative.A reversible off-on-type probe for p H sensing with fluorescence and SERS dual-signal output,Rhodamine-phenanthroline（RGP）,was designed and synthesized from Rhodamine 6G and 1,10-phenanthroline.Due to the molecular structure transformation between spirocyclic and ring-open forms,RGP exhibits varying fluorescence and SERS activities at different p H levels.The values of acidity constants（p Ka）and fluorescence quantum yield（F）of RGP were 2.43（±0.14）and 0.48,respectively.The fluorescence change of RGP was reversible and took place mainly within the p H range of 1.0 to 4.0.The SERS signals of RGP could be stable more than 3 h under room temperature and showed slight change after the p H of the sample solutionwas switched between 3.29 and 6.09 for 5 times.Most of the common inorganic ions and polycyclic aromatic hydrocarbons（PAHs）in water samples have little influence on the analytical performance of the probe.The present probe is simple and easy-to-use for the p H sensing in acidic media.