Editing Magnetic beads Preparation Methods (section)

== Coating ferrite MNPs with carboxyl groups (methacrylic acid) ==

[https://bomb.bio/ https://bomb.bio/]

Coating ferrite magnetic nanoparticles (MNPs, BOMB protocol #1.1) with carboxyl groups. The carboxyl-coated magnetic nanoparticles are synthesized by the classical radical polymerisation of methyacrylic acid (MAA) on the surface of ferrite magnetic core particles (protocol modified from Yu et al. [1]).&nbsp;

Chemicals

Ethanol (C2H6O, 99.9&nbsp;%) Honeywell/ Riedel-de Haёn 34963

Methacrylic acid, MAA (≥99%) (GC) Aldrich 155721

[https://www.tcichemicals.com/eshop/en/us/commodity/M0079/ https://www.tcichemicals.com/eshop/en/us/commodity/M0079/]

500g $26

Potassium persulfate (K2S2O8, ≥99%) Sigma-Aldrich 216224

Sodium dodecyl sulfate / SDS (C12H25NaO4S) Roth Chemicals CN30.3 2

Equipment and setup

Fume hood

Heated magnetic stirrer (e.g. IKAMAG REO)

Strong neodymium permanent magnet (e.g. NdFeB N45 40x40x20 mm)

Sterile plastic bottles

All procedures can be performed under inert N2 atmosphere or atmospheric oxygen conditions

1 Add 1 g (wet mass) of the synthesized iron oxide MNPs dispersed in 45 ml of water and 1.15 g sodium dodecyl sulfate to 200 ml of purified, degassed water in a 250 ml flask with stirring 5 min

2 Heat up the reaction solution to 70 °C 30 min

3 Add 0.96 ml of MAA into the flask. The pH value decreases to about 3, 5 min

4 Equilibrate the reaction mixture for about 45 min while keeping the temperature 45 min 

5 Add 1.98 g of initiator K2S2O8 to the solution 15 min

6 Let the polymerization reaction progress at 70 °C for 2 h 2 hours

7 Separate the coated MNPs using a strong neodymium magnet 15 min

8 Afterwards cool the reaction to room temperature 15 min

9 Remove free MAA and PMAA (poly(methacrylic&nbsp;acid)&nbsp;from the coated magnetic particles by a magnetic particle concentrator at room temperature 30 min

10 Disperse the isolated magnetic nanoparticles in deionized water in an ultrasonic bath, followed by magnetic extraction 5 min

11 Wash the beads with ddH2O at least 5 times or until the detergent is completely removed 1 h

12 Dispersed the magnetic particles in 250 ml of deionized water 5 min End Check the yield by weighing the wet mass of the beads ~7 h (2 h handson)

Store @ RT for up to 1 year

A 45 ml portion of the synthesized iron oxide colloid solution and 1.15 g sodium dodecyl sulfate were added to 200 ml of purified water in a 250 ml flask with mechanical stirring. After the reaction solution was heated to 70 oC, 0.96 ml of MAA was introduced into the flask. The pH value of the system was about 3. The reaction mixture was equilibrated for about 45 min at the same temperature before 1.98 g of initiator K2S2O8 was added to the solution. The polymerization was carried out at 70 oC in argon for 2 h, followed by cooling the reaction system to room temperature. To remove free MAA and PMAA, magnetic particles in the colloid solution obtained were extracted by a magnetic particle concentrator (Dynal MPC1-50, Dynal Biotech, France) at room temperature. The isolated magnetic nanoparticles were dispersed in deionized water under ultrasonication, followed by magnetic extraction. The washing process was repeated at least 5 times. A portion of the washed magnetic particles was freeze-dried for subsequent characterization.

Fig 1: Carboxyl-coated MNPs appear brownish (left vial) when compared to silica-coated MNPs (right vial, BOMB protocol #2.1)

References

1. Yu S, Chow CM. Carboxyl group (-CO2H) functionalized ferrimagnetic iron oxide nanoparticles for potential bio-applications. J Mater Chem. Royal Society of Chemistry; 2004;14: 2781–2786. doi:10.1039/b404964k