Photochemical Sensor Towards The Detection Of Food Safety Based On Nanoscales

Photochemical sensors, such as Fluorescence Spectroscopy, UV-vis, Surface Enhanced Raman Spectroscopy (SERS) are widely used and developed by researchers because of their high sensitivity and simplicity. In this thesis, a serious of new optical chemsensors are synthesized and investigated for their application in the detection of herbicide and food additive in agriculture products, which is high toxicity and high rudimental in food and have tremendous menace to the health of human being and environment. First, because of the surface plasma resonance (SPR) of gold nanoparticles, a simple, reliable and sensitive colorimetric visualization of melamine in milk by unmodified gold nanoparticles was developed. Then, based on this, we designed the aggregated gold nanoparticles, inverse opal of gold. The details are as follows:A simple, reliable and sensitive colorimetric visualization of melamine in milk products using citrate-stabilized gold nanoparticles (Au NPs). Upon exposure to ppb-level melamine, gold nanoparticle solution exhibits a highly sensitive color change from red to blue and rapid aggregation kinetics within the initial 5 min, which can directly be seen with the naked eye and monitored by UV-vis absorbance spectra. The melamine molecule itself contains multiple strong-binding sites to the surface of Au NPs and thus plays a role of molecular linker to efficiently crosslink Au NPs. Further evidence is that the sensitivity is significantly improved when NaHSO4 is added to promote the ligand exchange between citrate and melamine at the surface of Au NPs. The NaHSO4-optimized Au NPs system provides a rapid colorimetric assay for the rapid detection of melamine down to 25 ppb in real milk products.Based on the selectivity, sensitivity and low detection limit, we proposed a physical codeposition of gold inverse opal method. Gold nanoparticles were induced to the surface of sulfonic-capping PS micro spheres utilizing the electrostatic interaction between the gold cation and sulfonic group anion of PS microspheres. This down-up inverse opal structure was successful used in SERS for the detection of herbicide, such as 2,4-dichlorophenoacetie acid.