Magnetic Enrichment On Heavy Metal Ions And Detection Based On SERS

The scientific investigation revealed that several metallic elements were involved in the human body and they exhibited significant effect on the human health. The metal ions participated in some important biological processes. Although the content of metals in the body was very low, their role in the life process couldn't be ignored. Therefore, the enrichment and determination of the concentration has become particularly important. Herein, the heavy metal ions were immobilized onto the functionalized core shell nanoparticles by using the core-shell composite nanoparticles with magnetic core and noble metal shell. After applied a magnetic field, the core shell nanoparticles were enriched together with the heavy metal ions, the efficiency of magnetic enrichment was evaluated by surface enhanced Raman spectroscopy based on the assembly of sandwich structures. The main results were summarized as follows:1.Optimization on the SERS based approach for the determination of heavy metal ionsThe influences of different substrates on the assembly of the sandwich structures was compared, i.e. mechanical polished Au plate, atomic flat Au substrate and functionalized silicon substrate. The result showed that the SERS effect from the mechanical polished Au plate played a negative effect on the determination, while the complex modification procedure and the absence on coupling effect between the outer nanoparticles and substrate resulted in the low efficiency on the determination. However, in the absence of SERS effect and presence of the coupling effect that increased the sensitivity remarkably made the atomic flat Au film become the appropriate substrate for the assembly and SERS determination. The results revealed that the MBA molecule can be served as the functional molecule for the immobilization of heavy metal ions and the readout molecule for the SERS measurements. In order to investigate the coupling effect among the nanoparticles, the modified Au nanoparticles were connected by using the carboxyl chemistry of heavy metal ions, which provided the experimental basis for the SERS based determination.2.Introducing the magnetic composite nanostructures and achieving the magnetic enrichment of heavy metal ionsBy using coprecipitation method, the Fe₂O₃ core was prepared and the Au shell was covered onto the magnetic core through the reduction HAuCl4 solution. The shell thickness was controlled in order to obtain the reasonable magnetism from the core and an easy modification outer Au shell. The Au shell was attached self-assembly layer with the termination of carboxyl groups, and the heavy metal ions were immobilized onto the surface of core shell nanoparticles through the carboxylic coordination chemistry with metal ions. Applied external magnetic field, magnetic nanoparticles were enriched together with the immobilized heavy metal ions (Cu²⁺, Pb²⁺ and Zn²⁺). The relationship between the magnetic enrichment duration and the changes in the concentration of heavy metal ions was explored.3.Developing the high sensitive approach for evaluating the efficiency on the magnetic enrichmentThe sandwich structure of"MBA modified Au substrate/heavy metal ions/MBA modified Au nanoparticles"was built for the SERS determination. The readout of SERS signal from MBA indicated the existence of heavy metal ions and the possible range of the concentration. By comparing the change in the SERS signal of the sandwich structure assembled from the solution before and after the magnetic enrichment, the decrease in the concentration can be deduced. The results showed that the concentration for the 10^-2 mol/L Cu²⁺ solution decreased by 10 orders after the magnetic enrichment. This approach has become an appropriate candidate for evaluating the enrichment efficiency.4.Determining and magnetic enrichment on the chromium (VI) ionsBy the hydrogen bond of water between chromium (VI) and the carboxyl groups from MBA attached to the Au surface and Au nanoparticles, the sandwich structure of"MBA modified Au plate substrate/chromium (VI)-water/MBA modified Au nanoparticles"was built for SERS detection. Based on the above sandwich structure, functionalized Fe₂O₃@Au core-shell magnetic nanoparticles was introduced to enrich and separate chromium (VI) ions with the assistance of an external magnetic field. SERS detection showed that the concentration of chromium (VI) ions reduced by about 4-6 orders after the magnetic separation for the initial solution of 10^-5mol/L.