Investigation Of Noble Metal Nanoparticle Optical Probes For Colorimetric Detection Of Two Heavy Metal Ions

The rapid development of industrialization and human predatory exploitation of resources lead to serious heavy metal pollutants to natural water. Therefore, it is significant to realize the rapid and sensitive detection of heavy metal ions in water. At present, various methods have been reported for toxic heavy metal ions detection, which were mainly based on big analytical instruments. However, the high detection costs, complicated pre-treatment process and time-consuming limit their applications for on-site detection. Due to the unique optical and catalytic properties, the change of concentration, morphology and particle size of noble metal nanoparticles will cause the surface plasmon resonance absorption, which may result in color change of the nanoparticle dispersion. Thus, the colorimetric assay by eye vision or UV-vis absorption spectroscopy is applicable for the detection of heavy metal ions. However, the reported noble metal nanoparticle-based optical probes can only be used for the detection of single heavy metal ion or varied heavy metal ions detection but can not discrimination. However, the environmental real water may be polluted by two or more heavy metal ions. To further expand the application of the noble metal nanoparticle-based optical probes, in this thesis, we designed and developed new noble metal nanoparticle-based optical probes, which are responsive to two heavy metal ions and could be used for selective of two heavy metal ions via control of reaction conditions. Specific research contents are given below: 1) Study of Cu2+/ Mn2+ responsive silver nanoparticles(AgNPs)-based optical probe: The sodium pyrophosphate(Na4P2O7) and hydroxypropylmethylcellulose(HPMC)-stabilized AgNPs were prepared at room temperature using NaBH4 as a reducing agent. The AgNPs are well dispersed in water and the particles size is around 15 nm. Under an acidic condition, the AgNPs are gradually etched by Cu2+ resulting in changes of the solution color from yellow to colorless. Under an alkaline condition, however, the AgNPs aggregate immediately due to the coordination of P2O74- and Mn2+, resulting changes of the solution color from yellow to brown. Thus it can achieved colorimetric detection of Cu2+ and Mn2+, the limit of detections(LOD) of Cu2+ and Mn2+ by the naked eye respectively 0.05 and 0.5 μmol/L. Due to the silver nanoparticles surface plasmon resonance absorption is also changed, by UV-visible spectrophotometer(UV-vis) enables quantitative detection of low concentrations, the limit of detections(LOD) of Cu2+ and Mn2+ by UV-vis spectroscopy are respectively 2.0 and 20 nmol/L. Furthemore, the Cu2+/Mn2+ responsive silver nanoparticles(AgNPs)-based optical probe for Cu2+ or Mn2+ with excellent selectivity and validated by detection of Cu2+ and Mn2+ in real water samples. 2) Study of Cr3+/Cr2O72- responsive gold nanoparticles(AuNPs)-based optical probe: The functionalized AuNPs were prepared at room temperature using gallic acid as a reducing agent. The AuNPs are well dispersed in water and the particles size is around 30 nm. The GA-AuNPs can achieve rapid detection of Cr3+ in the presence of sodium thiosulfate and sodium citrate, no other ion interference. In addition, the GA-AuNPs can achieve rapid detection of Cr2O72- in the presence of ethylenediaminetetraacetic acid disodium salt(EDTA), no other ion interference. At the optimized experimental conditions, the Cr3+/Cr2O72- responsive AuNPs-based optical probe for Cr3+ and Cr2O72- with excellent selctivity and sensitivity. The study found that the AuNPs aggregate immediately due to the coordination of gallic acid and chromium(Cr3+/Cr2O72-), resulting changes of the solution color and the gold nanoparticles surface plasmon resonance absorption is also changed, based on the reaction mechanism can be achieved colorimetric detection of total chromium ions. The limit of the mixture of Cr3+ and Cr2O72- by eye vision is 1.5 μmol/L, and by UV-vis spectroscopy is 0.05 μmol/L. In the presence of masking agents(citrate and thiosulfate were applied to mask Cr2O72- for detection of Cr3+, and ethylenediaminetetraacetic acid disodium salt(EDTA) was applied to mask Cr3+ for detection of Cr2O72-), the GA-AuNPs can achieve detection of Cr3+ or Cr2O72-. The limit of the Cr3+ and Cr2O72- by eye vision are respectively 1.5 and 2.0 μmol/L, and those by UV-vis spectroscopy are respectively 0.1 and 0.1 μmol/L. The applicability of Cr3+/Cr2O72- responsive AuNPs-based optical probe is also validated by detection of Cr3+ and Cr2O72- in real water samples.