Detection Of Melamine And Thiocyanate, The Hazardous Materials In Food Based On Functional Gold Or Silver Nanoparticles

Owing to the specific optical, catalytic properties, noble nanoparticles materials(especially AuNPs and AgNPs) have been widely used in the fileds of material, biology and medicine etc. The functionalized AuNPs and AgNPs can be applied in the recognition of target substanc, based on the remarkable selectivity of nanoparticles. In this thesis, based on three different functionalized nanoparticles, we have successfully synthesized three functionalized nanoparticles which modified with different ligands and the quantitative methods of melamine and SCN- were proposed here. The main contents are shown as follows:1. The basic concepts and properties of noble metal nanoparticles were briefly described. The review for colorimetric detection of melamine, and the research for SCN- were summarized based on gold or silver nanoparticles.2. Introduction of the method of synthesis functionalized nanoparticles including CTA-AgNPs, SAA-AgNPs, and SAA-AuNPs, and the characterization of functionalized nanoparticles.3. Introduction of functionalized nanoparticles used for melamine detection:(1)Visual test for melamine using silver nanoparticles modified with chromotropic acidA simple and low-cost assay for melamine is introduced that is making use of silver nanoparticles(AgNPs) functionalized with chromotropic acid(CTA). The surface of the AgNPs was capped with chromotropic acid which warrants the NPs to remain in stable and dispersed form. The presence of melamine induces the aggregation of the CTA-AgNPs due to the hydrogen bond interaction between CTA and melamine. This is accompanied by a color change from yellow to orange which can be observed with bare eyes. The method allows melamine to be quantified by absorptiometry with a detection limit of 36 nM. The method was successfully applied to the determination ofmelamine in spiked liquid milk and the average recovery was 99 %. Most amino acids and a high content of calcium do not interfere in this assay.(2) Colorimetric detection of melamine in pretreated milk using silver nanoparticles functionalized with sulfanilic acidA simple, rapid and lower-cost assay with high sensitivity for the melamine detection in milk samples is introduced using sulfanilic acid-modi?ed silver nanoparticles(SAA-AgNPs). Due to the special chemical structures, SAA shows similar response to its analogues, which reveals that the selectivity and sensitivity of SAA itself is poor. However, the formation of SAA-AgNPs dramatically improves the selectivity of SAA and only melamine reacts with SAA-AgNPs. The possible mechanism is discussed. The interaction between exocyclic amine of melamine and SAA induces rapid aggregation of SAA-AgNPs accompanied by a naked-eye visible color change, resulting in precise quanti?cation of melamine that can be monitored by a simple UV-visible spectrometer. The detection limit is 10.6 nM, and the method is applied successfully to determine melamine in pretreated milk products, indicating the potential practical use for the products suspected of melamine exposure.(3) Colorimetric detection of melamine with sulfanilic acid-Au NPs in Milk and Biological SamplesA simple yet highly selective and sensitive assay for the detection of Mel is introduced using sulfanilic acid-functionalized gold nanoparticles(SAA–AuNPs). The interaction between Mel and SAA–AuNPs induces the aggregation and color change that can be spectrally monitored to precisely quantify the amount of Mel. The size, shape, and aggregation state of the AuNPs change after integration into a target application is critically investigated for optimizing performance. This approach shows excellent selectivity for Mel over its chemical analogues. The complex interference test including cations, anions, surfactants, sugars, and amino acids also suggests the potential on-site and real-time practical use of the sensor. The limit of detection of the proposed method was 38 nM and 1.2 nM in the concentration range of 0 to 1.2 μM and 1.2 μM to 2.2 μM, respectively. The confirmatory method is successfully applied to rapid determination of Mel in water, milk products, serum and urine.4. Two new methods of detect SCN- was estabilished based on AuNPs.(1) Colorimetric detection of thiocyante based on anti-aggregation of gold nanoparticles in the prescence of cetyltrimethyl ammonium bromideA facile, highly sensitive colorimetric strategy for thiocyanate(SCN?) detection is proposed based on anti-aggregation of gold nanoparticles(AuNPs) which was induced by surfactant cetyltrimethyl ammonium bromide(CTAB). A certain concentration of aggregation agent CTAB is responsible for a visible color change of AuNPs from wine red to blue. The aggregations of AuNPs decrease with increasing concentrations of SCN?, which can be monitored by an ultraviolet-visible spectrophotometer or the naked eyes. The limit of the detection(LOD) is 0.1 μM by the naked eyes and 6.5 nM by UV–vis spectroscopy with the linear range from 0.1 to 1.5 μM. The applicability of our detection system is also verified by analysis of SCN? in milk samples and satisfactory results were obtained.(2) Ultrasensitive turn-on ?uorescent detection of trace thiocyanate based on ?uorescence resonance energy transfer.A simple and ultrasensitive turn-on ?uorescence assay of trace SCN? is established based on the ?uorescence resonance energy transfer(FRET) between gold nanoparticles(AuNPs) and ?uorescein. The ?uorescence of ?uorescein is signi?cantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN?, the ?uorescence is turned on due to the competition action between SCN? and ?uorescein towards the surface of AuNPs. The ?uorescence enhancement ef?ciency [(IF-I0)/I0] displays a linear relationship with the concentration of SCN? in the range of 1.0 nM to 40.0 nM. The common anions, metal ions, amino acids and sugars have no obvious interference effects. The cost effective sensing system is successfully applied for the determination of SCN?in milk products and saliva samples. The detection limit is 0.09 nM.