Editing Magnetic beads Preparation Methods (section)

== IDA magnetic Beads ==

[https://onlinelibrary.wiley.com/doi/pdf/10.1002/bmc.3584 https://onlinelibrary.wiley.com/doi/pdf/10.1002/bmc.3584]

'''Synthesis of Fe3O4 particles&nbsp; (solvothermal method.)'''

The Fe3O4 particles were prepared via a solvothermal method as described previously (Xu et al., 2006). Briefly, 5.4 g of FeCl3 · 6H2O was first dissolved in 200mL of ethylene glycol under violent stirring. A clear yellow solution was obtained after filtration. Then 4.0 g of PEG 10000 and 14.4 g sodium acetate were added to this solution. The mixture was stirred vigorously for 30 min and then sealed in a Teflon-lined stainless-steel autoclave (200mL capacity). The autoclave was heated to and maintained at 200 °C for 12 h, and then allowed to cool to room temperature. The black products were washed several times with ethanol and deionized water and dried at 60 °C for 8 h.

'''Synthesis of Fe3O4@SiO2 (sol–gel method)'''

The core–shell Fe3O4@SiO2 nanocomposites were prepared using a modified method from Stöber et al. (1986). The core–shell Fe3O4@SiO2 magnetic microspheres were synthesized by a sol–gel process to coat a thin layer of dense amorphous silica on Fe3O4 nanoparticles. Briefly, an ethanol dispersion of the magnetite particles (150mg) was added to a beaker and washed three times with deionized water with help of the permanent magnet. Then, 50mL of 0.1mol/L HCl solution was added followed by ultrasonication for 30min. The supernatant was decanted and the superparamagnetic Fe3O4 nanoparticles were added to a three-neck round-bottom flask and dispersed in 80mL ethanol and 20mL deionized water by ultrasonication for about 10min. Under continuous mechanical stirring, 1.0mL of ammonium hydroxide (28 wt%) and 0.8mL of TEOS were consecutively added to the reaction mixture. The reaction was allowed to proceed at 30 °C for 6 h under continuous stirring. The resultant product was obtained by magnetic separation with help of the permanent magnet and was thoroughly washed with ethanol and deionized water six times (50mL each time). The product was then dried under vacuum at 60 °C for 8 h.

silica was coated on the Fe3O4 using a sol–gel method to form Fe3O4@SiO2 core–shell microspheres through hydrolysis of TEOS according to the Stöber method. Because the surface of Fe3O4 has a strong affinity toward silica, no primer was required to promote the deposition and adhesion of silica. The growth of silica shells on Fe3O4 nanoparticles involved the base-catalyzed hydrolysis of TEOS and subsequent condensation of silica onto the surfaces of Fe3O4 cores. Several parameters (such as the growth time and the concentration of ammonia catalyst or water) can be employed to control the thickness of silica shell on the Fe3O4 surface. It is found that the particle size can be conveniently adjusted by changing the concentration of TEOS precursor.



Preparation of IDA-modified Fe3O4@SiO2 magnetic microspheres

The IDA-modified Fe3O4@SiO2 magnetic microspheres were prepared using the Fe3O4@SiO2 magnetic microspheres modified with IDA as chelating ligand and are shown in Scheme 1. Briefly, 2.5 g IDA was dissolved in 50mL of a 2mol/L solution of Na2CO3, and the pH was adjusted to 10.0 with 10mol/L NaOH. The IDA solution was stirred for several minutes in an ice bath and then'''3-glycidoxypropyltrimethoxysilane '''(1.6mL) was added into the solution slowly. After 30min of stirring at 0°C, the reaction mixture was allowed to warm up to 65°C with stirring. After 6 h, the reaction solution was cooled to room temperature and the pH was adjusted to 6.0 with concentrated HCl. One gram of Fe3O4@SiO2 magnetic microspheres was added to the above solution and ultrasonicated for 10min. The suspension was heated at 95°C for 2 h with stirring. The resulting nanoparticles denoted superparamagnetic IDA silica were separated with help of the permanent magnet and washed thoroughly with deionized water six times (50mL each time). Charging of Fe3O4@SiO2–IDA magnetic microspheres with metal ions Charging of Fe3O4@SiO2–IDA magnetic microspheres with metal ions (eg. Cu2+, Ni2+ and Zn2+ ions) was performed as follows: 60mg of Fe3O4@SiO2–IDA magnetic microspheres were mixed with 50mL of aqueous solution of CuSO4 (10mg/mL). The mixture was stirred magnetically at 100 rpm for 3 h. Then the excess unbound Cu2+ was removed with water. The same method was followed to chelate Ni2+ or Zn2+ using the aqueous solution of NiSO4 or ZnSO4 (10mg/mL).

[[File:IDA magnet.png|700px|IDA magnet.png]]

'''Charging'''

60mg of Fe3O4@SiO2–IDA magnetic microspheres were mixed&nbsp;with 50mL of aqueous solution of CuSO4 (10mg/mL). The mixture&nbsp;was stirred magnetically at 100 rpm for 3 h. Then the excess&nbsp;unbound Cu2+ was removed with water. The same method was&nbsp;followed to chelate Ni2+ or Zn2+ using the aqueous solution of&nbsp;NiSO4 or ZnSO4 (10mg/mL).

'''Regeneration''' of Fe3O4@SiO2@IDA–metal ions magnetic microspheres:&nbsp;50 mM EDTA,







[[File:IDA Silica MagBeads.png]]

Highly selective magnetic affinity purification of histidine-tagged proteins by Ni2+ carrying monodisperse composite microspheres

Synthesis of magnetic SiO2 (SiO2@Mag-SiO2) microspheres The poly(glycidyl methacrylate), poly(GMA), seed latex 2.1 mm in size was synthesized by dispersion polymerization of GMA.32 Monodisperse-porous poly(methacrylic acid-co-ethylene dimethacrylate), poly(MAA-co-EDMA) microspheres 6 mm in size were obtained by using multi-step microsuspension polymerization technique.33,34 The magnetization of poly(MAA-co-EDMA) microspheres was performed as described elsewhere.35 The magnetic poly(MAA-co-EDMA) microspheres were used as a template for synthesis of monodisperse, magnetic SiO2 microspheres. Briey, the poly(MAA-co-EDMA) microspheres were dispersed in an aqueous solution containing TBAI, ammonia, 2-propanol and distilled water for 1 hour under mechanical stirring. TEOS solution (in IPA containing 50 w/w%) was added dropwise into the solution and stirred for 24 h at R.T. The formed silica-gel/poly(MAA-co-EDMA) composite microspheres were then separated by a magnet and washed with IPA and distilled water 3 times. The magnetic microspheres were dried in vacuum at 60 C for 24 h. The calcination was carried out at 450 C for 10 h for formation of the magnetic, monodisperse SiO2 microspheres. Finally, SiO2 coating onto the MagSiO2 microspheres (SiO2@Mag-SiO2) was done with the same process as described above.31 2.3 Synthesis of iminodiacetic acid attached magnetic SiO2 (IDA–GLYMO@SiO2@Mag-SiO2) microspheres The synthesis of iminodiacetic acid–(3-glycidoxypropyl)trimethoxysilane (IDA–GLYMO) precursor was performed by using a modied form of the protocol reported previously:36 IDA (0.53 g) was dissolved in 10 mL of DDI water, and pH of solution was adjusted to 11.0 with 10.0 M NaOH. The obtained solution was transferred into a Pyrex® reactor placed in an ice-bath at 0 C, and 0.4 mL of GLYMO was slowly added under stirring. The solution was heated to 65 C for 6 h with stirring, subsequently placed into an ice-bath for 10 min to decrease the temperature to 0 C. 0.4 mL of GLYMO was again added and the temperature was increased to 65 C for another 6 h under stirring. Finally, pH of IDA–GLYMO solution was adjusted to 3 with concentrated HCl. In order to attach IDA–GLYMO precursor onto the SiO2@Mag-SiO2 microspheres, 0.2 g of microspheres were added to IDA–GLYMO solution at pH 3 and the resulting dispersion was heated at 95 C for 2 h with mechanical stirring. The resulting IDA–GLYMO@SiO2@Mag-SiO2 microspheres were extensively washed with DDI water and nally dispersed in DDI water. 2.4 Ni2+ attachment onto IDA–GLYMO@SiO2-Mag-SiO2 microspheres Ni2+-immobilized IDA–GLYMO@SiO2@Mag-SiO2 (Ni2+–IDA– GLYMO@SiO2@Mag-SiO2) microspheres were prepared by the incubation of IDA–GLYMO@SiO2@Mag-SiO2 microspheres (20 mg) in 0.25 M aqueous NiCl2 solution at RT for 2 h under gentle stirring. The obtained Ni2+–IDA–GLYMO@SiO2@Mag-SiO2 microspheres were collected by magnetic separation and washed with distilled water several times to remove free Ni2+ ions. In this case, each Ni2+ ion coordinates to more than one carboxyl groups (–COOH) via metal(II) carboxyl chemistry.