All chemicals were purchased from Sigma-Aldrich Corporation (MO, USA) and used as received without further purification. Deionized water was used throughout. The TEM images were taken using a JEOL 2000EX transmission electron microscope (JEOL Ltd., Tokyo, Japan) at an accelerating voltage of 200 kv. The UV–vis spectra were taken by Lambda 950 UV–vis spectrometer (PerkinElmer, MA, USA).
In this method, magnetite nanoparticles were prepared first in water solvent by the chemical precipitation method. Then, gold precursor was added in the solution and reduced by Fe2+
which was oxidized to Fe3+
. Magnetite change to maghemite and attach on gold nanoparticles (as shown in Figure ). In a typical process, a mixture of 0.1
mmol of FeCl2
mmol of FeCl3
O and 0.1
mmol D-lysine in 50
ml deionized water was stirred and bubbled with N2
min, and then, 0.6
ml of 5
N ammonium was added in the mixture under N2
protection. The color of the mixture changed to black immediately while the mixture was continually stirred for another 30
min and added with 2
ml of 0.05
aqueous solution drop by drop into the black mixture. The color changed to purple black slowly while on continuous stirring for 60
min. Separated by external magnate, the liquid was almost colorless, and the paste was purple black which was washed by deionized water and separated by external magnate three times. The final product, which was purple black solution, was redispersed in deionized water for further measurement. Figure shows the procedure of formation of maghemite-gold bifunctional nanomaterials. Inset photo is the final product in water, which shows the purple-black solution.
Schematic of the formation of maghemite-gold bifunctional nanomaterials.
Protein separation is one of the basic applications of this kind of bifunctional nanomaterials. To use these materials for protein separation, the sample was washed several times to make sure there is no free gold nanoparticle in the solution, and bovine serum solution was added in the sample. Then, by using external magnetic separation, the sample was divided to liquid and paste, which was redispersed in water, for SDS-PAGE electrophoresis gel stained by Coomassie blue. Figure shows the mechanism for protein separation by the bifunctional nanocomposite.
Schematic of the protein separation by the nanocomposite.