Editing Magnetic beads Preparation Methods (section)

== Magnetic core nanoparticles synthesis ==

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A simple co-precipitation protocol for preparation of magnetic nanoparticles (MNP). It relies on forming Fe3O4 magnetic particles during co-precipitation of FeCl2 and FeCl3 in alkali solutions [1]. The formed MNPs have a diameter of ~5-20 nm. Oxygen is known to interfere with the synthesis, therefore the reactions can be either flushed with N2 for at least 30 minutes, performed immersed in argon or degassed and preheated to 80 °C right before the synthesis.&nbsp;

Iron (II) chloride 4-hydrate puriss ≥99% (FeCl2 · 4 H2O) Honeywell/Fluka 44939

Iron (III) chloride, anhydrous, pure (FeCl3) Roth Chemicals 5192.3

Sodium hydroxide, ≥99% (NaOH) Roth Chemicals 6771.1

37% HCl fuming Roth Chemicals 4625.1

Ammonia solution (NH4OH, 25%) EMD Millipore 1.05432



'''Buffers and solutions'''

2 M NaOH (prepare 0.5 L) –can be stored at RT for at least 12 months

0.1 M HCl (prepare 0.5 L) – can be stored at RT for at least 12 months

Fe2/3 solution (prepare freshly 60 ml)

0.333 M FeCl3 (3.24 g FeCl3)

0.167 M FeCl2 (2 g FeCl2 · 4 H2O)

Dissolve with magnetic stirring in 60 ml of 0.1 M HCl solution

'''Equipment'''

Fume hood Magnetic stirrer with heating (e.g. IKAMAG REO)

Strong neodymium permanent magnet (e.g. Neodymium disc magnet 80x10 mm grade N45 adhesive force ~300 kg – be extremely careful when using such strong magnets!)

Sterile plastic 0.5 L bottle (e.g. Corning® Costar®, Nunc® T175 uncoated PS flask)

Protective clothing (lab coat, eye protection, hand gloves)

'''Experimental setup''' [[File:Magnetic nanoparticles reaction.png|RTENOTITLE]]

All procedures can be performed under inert argon atmosphere (alternatively purging the system with high purity N2 for 30 minutes should be sufficient. We generally perform the reaction at atmospheric oxygen levels yet degas and heat up the solutions before use)

1 Assemble the reaction bottle and the dripping funnel and place on a magnetic stirrer, add 100 ml of degassed 2 M NaOH to the collection flask on the bottom and the Fe2/3 solution to the dripping funnel. Heat up the flask containing the 2 M NaOH solution to 80-85 °C. 10 min

2 Add drop wise the 60 ml Fe2/3 solution into 100 ml of preheated (80-85 °C) 2 M NaOH solution under vigorous stirring (>400 rpm) 20 min

Black precipitate of Fe3O4 (FeO·Fe2O3) is formed

3 After the complete Fe2/3 solution was added, add 10 ml of 25% ammoniac to the reaction mixture and stir for a further 30 minutes and then cool to RT 30 min

4 Transfer the solution to a sterile plastic container and magnetically pellet the black precipitate (MNPs), discard the supernatant 5 min

5 Resuspend in 200 ml of ddH2O, pellet magnetically and discard supernatant. Repeat for a total of 5 washes (or until the pH of the wash reaches ~7) 1 h

6 After the last wash resuspend the MNPs in 30-40 ml of ddH2O and transfer to a fresh 50 ml tube

End To measure the synthesis yield, magnetically pellet the MNPs, remove the water and weigh the product wet-mass, alternatively flash freeze the pelleted MNPs in liquid nitrogen and lyophilise and measure the dry mass ~2 h (~1 h hands-on) Lyophilised MNPs under N2 or argon atmosphere can be stored in a closed container at RT for a longer time, the wet MNPs slowly oxidise over time, therefore we functionalise them further within a week

Modifications Different protocols provide MNPs with different properties. This protocol was selected and optimized for robustness and because it yields relatively small sized magnetic particles (~5-20 nm in diameter as judged by the TEM images). However, a plethora of other methods can be employed for the synthesis of suitable MNPs as reviewed in [2].



'''No precipitate formed'''

Use freshly made alkali solutions, correct iron salts at indicated concentrations; Preheat the alkali solution to at least 70 °C or degas before adding the Fe2/3 solution

'''Precipitate not magnetic'''

Make sure you are using freshly made Fe2/3 solution and that you have used correct iron salts for the mixture