Fabrication Of Nanomaterials-based Colorimetric Sensors For Food And Environmental Analyses

Nanomaterials are defined as compounds between macroscopic materials and atoms with the size less than 100 nm in one or more dimensions of space.As typical metal nanomaterials,gold and silver nanomaterials have become research hotspots in recent years due to their unique physical,chemical and biological properties.It has been shown that the physicochemical properties of metal nanomaterials depend on their morphology and size,and different morphologies and sizes result in different localized surface plasmon resonance（LSPR）,surface catalytic activity and biocompatibility.Thereby,developing metal nanomaterials based colorimetric sensors for ultrasensitive determination of target analytes in complex matrices such as environmental and food samples have attracted much attention in recent years.As a consequence,the present study is going to fabricate applicable colorimetric sensors for food and environmental analyses by taking advantage of regulating of anti-aggregation of gold nanoparticles（AuNPs）,the etching process of gold nanoplates（AuNPLs）and the catalytic activity of silver nanoparticles（AgNPs）involving in the reduction system of 4-nitropheno-NaBH₄.The as-proposed assays were successfully employed for the quantitative analysis of ultra-trace of I^-,Cu²⁺and Hg²⁺,TCs in food and environmental water samples,respectively.The main content of this thesis is as follows:1.A novel anti-aggregation of AuNPs strategy for colorimetric sensing of I^-was proposed.The anti-aggregation of AuNPs was regulated by the redox reaction between the target ions and the ion cross-linking agent.AuNPs（¹3 nm in diameter）were prepared by the citrate reduction of HAuCl₄.The obtained AuNPs were characterized by transmission electron microscopy,UV-vis spectrophotometer and nanoparticles size analyzer.By investigating the effects of arginine（Arg）and Cu²⁺concentration,reaction time and pH on the aggregation state of AuNPs,the mechanism of aggregation/anti-aggregation of AuNPs was illustrated.The corresponding processes were monitored by visual or UV-vis spectroscopy.Under optimal conditions,this assay showed high sensitivity with a lowest detectable concentration of 10?nmol L^-11 for the detection of I^-,and it was desirable when being applied for the detection of I^-in drinking water and table salt samples.2.AuNPLs based colorimetric sensor for ultrasensitive sequential detection of Cu²⁺and Hg²⁺was developed.AuNPLs with edge length about 70 nm were synthesized according to the rapid seedless growth method.The size,morphology and optical properties of the prepared AuNPLs were investigated by transmission electron microscopy and UV-vis.The etching mechanism of AuNPLs was further illustrated by analyzing the resulted product during the etching process using mass spectrometry.The results showed that the colorimetric sensor for detection of Cu²⁺and Hg²⁺in successive has good selectivity and high sensitivity within a wide linear range.Cu²⁺showed good linearity in the range of 0.05–1.5μmol L^-1 with the detection limit of 19 nmol L^-1,and Hg²⁺had a good linearity in the range of 0.02–3μmol L^-1 with the detection limit of 9 nmol L^-1.3.A multi-mode detection of tetracycline antibiotics（TCs）based on the catalytic action of AgNPs in the reduction system of 4-nitropheno-NaBH₄ was proposed.AgNPs with diameters about 10 nm were prepared through the citrate reduction of silver nitrate.The catalytic activities of AgNPs modified with different concentrations of TCs on the reduction system of 4-nitropheno-NaBH₄ were monitored by chronoscope and UV-vis spectra.This method is sensitive for TCs detection without requiring any expensive equipment.Under the optimal conditions,the lowest detectable concentrations by the chronometric and colorimetric method were 6 nmol L^-1 and 34 nmol L^-1,respectively.The as-developed methods were successfully applied for the detection of TCs in various environmental water samples.