Editing Magnetic beads Preparation Methods (section)

== Silica-Coated Magnetic Nanoparticles ==

A magnetic fluid with particles with a size of 15 nm are prepared by using conventional coprecipitation of Fe3+ and Fe2+ ions by OH<sup>-1</sup>&nbsp;at room temperature. In a typical synthesis, 4.17 g of FeCl3.6H2O and 1.52 g of FeCl2.4H2O (such that Fe3+/Fe2+ = 2) are dissolved in 80 ml of water (concentration of Fe2+ is 0.1 M) with vigorous stirring. A solution of 6 ml of 35&nbsp;% NH4OH is added at a rate of 1 drop per second at room temperature during constant stirring. Black precipitates of Fe3O4 (FeO.Fe2O3) are formed and isolated from the sol-vent by magnetic decantation. The water washing and the decantation process are repeated four times to remove excess solution. In a similar way, Fe<sub>1~x</sub>Ni <sub>x</sub>O.Fe2O3 and Fe<sub>1~y</sub>Co<sub>y</sub>.Fe2O3 nanoparticles with x = 0.05, 0.1, 0.2, 0.5 and y = 0.2, 0.4 are made by using NiCl2.6H2O and CoCl2.6H2O, respectively to replace Fe2+ by Ni2+ and Co2+. All procedures are conducted under a N2 atmosphere. To study the oxidation of bare NPs, after washing, we dried the FeO.Fe2O3, Fe<sub>1~x</sub>Ni<sub>x</sub>O.Fe2O3 and Fe<sub>1~y</sub>Co<sub>y</sub>.Fe2O3 nanoparticles and exposed them in&nbsp;air for them to be oxidized; then we measured the magnetic properties. To see the effect of surfactant coating, we vigorously mixed the precipitates in water with&nbsp;polyisobutylene-modi ed-polysuccinimide (PIB-PS) and<br/>then redisperse them in hexane as the carrier liquid. The hexane washing and the decantation are conducted four&nbsp;times to remove excess PIB-PS in the solution. After<br/>that, the PIB-PS-coated nanoparticles&nbsp;&nbsp;are dried and exposed in air for them to be oxidized.



'''Synthesis of Silica-Coated Magnetic Nanoparticles'''

[https://www.hindawi.com/journals/jnm/2013/603940/ https://www.hindawi.com/journals/jnm/2013/603940/]

Magnetic Fe3O4 nanoparticles were synthesized by using coprecipitation from iron (III) chloride and iron (II) chloride solutions with the assistance of aqueous ammonia solution as described elsewhere [6]. The synthesized magnetic nanoparticles were washed several times with alcohol and then distilled water until pH 7.0. Fe3O4/SiO2 nanoparticles were prepared by coating magnetic nanoparticles with silica. 100 mL of the suspension of prepared magnetic nanoparticles (containing 1 g magnetite) was stored in a flask. 50 mL of the 10% solution of aqueous '''tetraethylorthosilicate '''(TEOS) was added to the flask together with 70 mL alcohol and mixed using an overhead stirrer. The pH of the suspension was adjusted to 9.0 with NaOH. The flask was then heated to 90°C and stirred at this temperature for 6 h. After cooling to room temperature (RT), the suspension was washed twice with alcohol and six times with distilled water. The final suspension volume was adjusted to 100 mL with water.



Fe3O4/SiO2 nanoparticles were characterized using a transmission electron microscope (TEM JEM1010, JEOL) and Fourier-transform infrared (FTIR) spectroscopy (FT/IR-6300, JASCO). Magnetic curves were measured using a DMS-880 vibrating sample magnetometer (VSM) at RT.



1. 0.02~0.42 mole of FeCl3 and 0.02~0.3 mole of FeCl2 in 18~500 ml water was heated at 60~90° C. for 10~30 minutes to obtain a mixture.

2. The above mixture was mixed with 5~25% of alkaline solution and stirred at 60~90° C. for 20~45 minutes to form magnetic cores.

3. Cooled the magnetic cores to room temperature. 4. Alkaline solution (0.05X ~ 0.1X volumes) and ethanol (1X ~3 X volumes) were then mixed to step 3.

5. Tetraethyl orthosilicate (TEOS) was added to step 4 in various ratio (0.05%~&nbsp;%) to coat the magnetic cores with silica forming silica-coated magnetic beads.

6. The silica-coated magnetic beds were incubated overnight at room temperature.

7. The silica-coated magnetic beads were washed sequentially by ethanol and ddH2O.

8. The silica-coated magnetic beads were finally stored in ddH2O at room temperature.

'''DNA isolation'''

For further experiments in nucleic acid isolation, Fe3O4/SiO2 nanoparticles were stored in 100 mM Tris-HCl buffer (pH 7.0). For each DNA isolation reaction from 200 μL serum sample, 50 μL of Fe3O4/SiO2 nanoparticles at a concentration of 25 mg/mL was used.

2.2. Preparation of DNA Isolation Buffers A set of nucleic acid buffers were made based on the method described previously by Boom et al. [1] and optimized in this work suitably for properties of Fe3O4/SiO2 nanoparticles. The set contained (i) Proteinase K 20 mg/mL (BioBasic), (ii) lysis buffer (LB: 30 mM Tris-HCl pH 7.0, 1 M NaCl, 4.5 M GuSCN, 20 mM EDTA, 1.5% Triton X-100), (iii) two types of washing buffers (WB1: 30 mM Tris-HCl, pH 7.0, 2.25 M GuSCN, 56% ethanol; WB2: 10 mM Tris-HCl pH 7.0, 70% ethanol), and (iv) elution buffer (EB: 10 mM Tris-HCl pH 8.5, 1 mM EDTA).

three ways to protect nanoparticles from&nbsp;oxidation: (a) using a highly viscous carrier liquid, which&nbsp;limits the dilusion of oxygen; (b) using relevant surfactants, PIB-graft-PS and PIB-block-PS; (c) substitution&nbsp;of Ni2+ and Co2+ for Fe2+ in the structure of magnetite.&nbsp;In (b) the hydrophobic tail (PIB) should be a saturated,&nbsp;straight hydrocarbon chain and the hydrophobic head&nbsp;(PS) should be amine group.