| Surface-enhanced Raman spectroscopy(SERS)technology,as a novel trace analysis technology,has several advantages,such as providing fingerprint spectra,high sensitivity,fast analysis speed and simple determination.It has been widely used in many fields such as food safety,environmental monitoring and public safety.Gold and silver colloidal nanoparticles have become the most popular and widely used SERS substrates because they are simple to prepare and easy to use especially in the field of rapid detection.In order to achieve rapid and sensitive SERS detection,two requirments need to meet.First,hot spots need to be generated by the aggregation of nanoparticles.Second,the analyte is adsorbed on or near the surface of the nanoparticles.In this thesis,based on the gold and silver colloidals substrates,different SERS enhancement strategies through different surface modification and interface interaction were developed and applied to the quantification of different types of targets.The contents completed in this thesis are as follows:(1)For the two targets of sodium saccharin with strong adsorption to the metal surface and morphine with weak adsorption,based on the Au nanoparticles(Au NPs)reduced by sodium citrate,the effects of different sodium salts on the aggregation and SERS performance were studied.The results showed that the SERS performance was not only related to the aggregation but also the effective adsorption.For the strongly adsorbed sodium saccharin,compared to NaNO3 and Na2SO4,NaCl had a better aggregation effect due to the formation of Au-Cl bond,resulting in better SERS performance;For the weakly adsorbed morphine,NaF,NaCl and NaBr had the equivalent SERS performance,while NaI was about 3 times worse,which mainly depended on the effective adsorption of molecules,especially the directly adsorbed molecules.The influence of the reagent adding orders was first explored,and the results showed that the change of the reagent adding orders can control SERS sensitivity and reproducibility.The best adding order is"in the analyte solution,first add the halide salt and mix,then add Au NPs".Under the best conditions,the quantitative analysis methods of saccharin sodium and morphine were successfully established,and the detection limits were as low as 0.5 and 0.01 mg L-1,respectively,and SERS detection of saccharin sodium in different beverage matrices was realized.(2)Taking paraquat with better water solubility as the targets,the superhydrophobic surface of the natural lotus leaf was utilized to realize the simultaneous concentration and aggregation of silver nanoparticles(Ag NPs)and the analyte,which produced abundant effective hot spots and the concentrated analytes were confined in the hot spots.A green,cost-effective and efficient SERS sensor based on the lotus leaf was built.Compared with traditional aggregation on the glass,and the sensitivity was improved about 20 times.The SERS sensor was not affected by the state of the lotus leaf including storage time,sampling sites or growth stages of lotus leaf,had a certain degree of anti-interference to organic solvents and salts,and was not limited by the type of colloidals such as Au NPs,gold nanorods(Au NRs),and sodium phytate-silver nanoparticles(IP6-Ag NPs).The SERS sensor had good reproducibility(Relative standard deviation(RSD)was less than11.6%),and the quantitative analysis method of paraquat was successfully established with the detection limit as low as 1.2?g L-1,and the SERS determination of paraquat in actual water samples(drinking water,tap water and lake water)were realized.(3)For three illegal additives(auramine O,Sudan ? and Sudan ?)with large differences in hydrophobicity,Ag NPs were used as reinforcing particles,and cationic surfactants with different carbon chain lengths were selected as aggregation agents and modifiers to prepare nano-Ag aggregates with different hydrophobicity.The effects of concentrations and structures(carbon chain lengths)of the surfactants on the aggregation of Ag NPs were studied,and the aggregation mechanism was deduced.The matching relationship between the hydrophobicity of three illegal additives and the above different hydrophobic substrates were studied.It was found that nano-Ag aggregates with matching hydrophobicity can be constructed by adjusting the carbon chain lengths of the surfactants.The sensor platform had good reproducibility(RSD<6.6%),and it can realize highly sensitive quantitative analysis of auramine O,Sudan ? and Sudan ?.The detection limits were as low as 6.1×10-8,7.5×10-9,2.1×10-9 mol L-1,respectively.The platform successfully achieved rapid and sensitive quantitative detection of Sudan I in different food matrices.(4)In order to achieve the selective detection of hydrophobic trinitrotoluene(TNT),Au NPs were used as SERS reinforcing particles,the chemical transformation strategy by forming Meisenheimer complexes between TNT and cysteamine(Cys)was adopted.Au NPs were induced to aggregate with Au-S bond,and TNT molecules were localized in the hot spots generated by aggregation at the same time.The detection of TNT with high selectivity and sensitivity was achieved.The effects of the concentrations of Meisenheimer complexing agents,pH and the type of complexing agents were systematically investigated.It was found that when the concentration of Cys was moderate(10-4mol L-1),and pH value of the system was 9,TNT had the strongest SERS signals.By replacing Cys with 2-dimethylaminoethylthiol,although the steric hindrance of the amino group was obviously increased from the primary amine to the tertiary amine,it can still react with the electron-deficient TNT to achieve SERS detection.This method had high selectivity,even picric acid molecules with highly similar structures did not affect SERS detection.The method had good reproducibility(RSD<10.2%),and it was successfully used for quantitative analysis of TNT,with the detection limit as low as 0.001 mg L-1. |
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