This work was generously supported by Brown University and the Advanced Energy Consortium. We gratefully thank Dr. Qingbo Zhang for his established synthetic method of iron oxide MFCs.

1. Synthesis of MFCs with control over MFCs&#39; overall diameter and ferrite composition
<ol>
	<li>Wash and thoroughly dry all glassware to be used in the synthesis. The amount of water in the synthesis impacts the dimensions of the MFCs, so it is crucial to ensure the glassware has no residual water in it16,26.
	<ol>
		<li>To wash the glassware, rinse with water and detergent and scrub with a flask brush to remove debris. Thoroughly rinse to ...

<ol>
	<li>Makridis, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+application+of+Mn-ferrite+nanoparticles+as+novel+magnetic+hyperthermia+agents.">In vitro application of Mn-ferrite nanoparticles as novel magnetic hyperthermia agents.</a> Journal of Materials Chemistry B. 2 (47), 8390-8398 (2014).</li><li>Nelson-Cheeseman, B., Chopdekar, R., Toney, M., Arenholz, E., Suzuki, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interplay+between+magnetism+and+chemical+structure+at+spinel-spinel+interfaces.">Interplay between magnetism and chemical structure at spinel-spinel interfaces.</a> Journal of Applied Physics. 111 (9), 093903 (2012).</li><li>Otero-Lorenzo, R., Fantechi, E., Sangregorio, C., Salgueiri&#241;o, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvothermally+driven+Mn+doping+and+clustering+of+iron+oxide+nanoparticles+for+heat+delivery+applications.">Solvothermally driven Mn doping and clustering of iron oxide nanoparticles for heat delivery applications.</a> Chemistry-A European Journal. 22 (19), 6666-6675 (2016).</li><li>Mohapatra, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+magnetic+heating+efficiency+in+size+controlled+MFe+2+O+4+(M=+Mn,+Fe,+Co+and+Ni)+nanoassemblies.">Enhancement of magnetic heating efficiency in size controlled MFe 2 O 4 (M= Mn, Fe, Co and Ni) nanoassemblies.</a> Rsc Advances. 5 (19), 14311-14321 (2015).</li><li>Qi, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carboxylic+silane-exchanged+manganese+ferrite+nanoclusters+with+high+relaxivity+for+magnetic+resonance+imaging.">Carboxylic silane-exchanged manganese ferrite nanoclusters with high relaxivity for magnetic resonance imaging.</a> Journal of Materials Chemistry B. 1 (13), 1846-1851 (2013).</li><li>Anandhi, J. S., Jacob, G. A., Joseyphus, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+the+heating+efficiency+of+Mn-doped+Fe3O4+nanoparticles.">Factors affecting the heating efficiency of Mn-doped Fe3O4 nanoparticles.</a> Journal of Magnetism and Magnetic Materials. 512, 166992 (2020).</li><li>Del Bianco, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanism+of+magnetic+heating+in+Mn-doped+magnetite+nanoparticles+and+the+role+of+intertwined+structural+and+magnetic+properties.">Mechanism of magnetic heating in Mn-doped magnetite nanoparticles and the role of intertwined structural and magnetic properties.</a> Nanoscale. 11 (22), 10896-10910 (2019).</li><li>Padmapriya, G., Manikandan, A., Krishnasamy, V., Jaganathan, S. K., Antony, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+catalytic+activity+and+magnetic+properties+of+spinel+Mn+x+Zn+1&#8722;x+Fe+2+O+4+(0.0&#8804;x&#8804;1.0)+nano-photocatalysts+by+microwave+irradiation+route.">Enhanced catalytic activity and magnetic properties of spinel Mn x Zn 1&#8722;x Fe 2 O 4 (0.0&#8804;x&#8804;1.0) nano-photocatalysts by microwave irradiation route.</a> Journal of Superconductivity and Novel Magnetism. 29 (8), 2141-2149 (2016).</li><li>Kim, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+O2-evolving+MnFe2O4+nanoparticle-anchored+mesoporous+silica+nanoparticles+for+efficient+photodynamic+therapy+in+hypoxic+cancer.">Continuous O2-evolving MnFe2O4 nanoparticle-anchored mesoporous silica nanoparticles for efficient photodynamic therapy in hypoxic cancer.</a> Journal of the American Chemical Society. 139 (32), 10992-10995 (2017).</li><li>Silva, L. H., Cruz, F. F., Morales, M. M., Weiss, D. J., Rocco, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+targeting+as+a+strategy+to+enhance+therapeutic+effects+of+mesenchymal+stromal+cells.">Magnetic targeting as a strategy to enhance therapeutic effects of mesenchymal stromal cells.</a> Stem Cell Research &amp; Therapy. 8 (1), 1-8 (2017).</li><li>Otero-Lorenzo, R., Ramos-Docampo, M. A., Rodriguez-Gonzalez, B., Comesan&#771;a-Hermo, M., Salgueiri&#241;o, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvothermal+clustering+of+magnetic+spinel+ferrite+nanocrystals:+a+Raman+perspective.">Solvothermal clustering of magnetic spinel ferrite nanocrystals: a Raman perspective.</a> Chemistry of Materials. 29 (20), 8729-8736 (2017).</li><li>Aghazadeh, M., Karimzadeh, I., Ganjali, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PVP+capped+Mn2++doped+Fe3O4+nanoparticles:+a+novel+preparation+method,+surface+engineering+and+characterization.">PVP capped Mn2+ doped Fe3O4 nanoparticles: a novel preparation method, surface engineering and characterization.</a> Materials Letters. 228, 137-140 (2018).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvothermal+synthesis+of+MnFe+2+O+4+colloidal+nanocrystal+assemblies+and+their+magnetic+and+electrocatalytic+properties.">Solvothermal synthesis of MnFe 2 O 4 colloidal nanocrystal assemblies and their magnetic and electrocatalytic properties.</a> New Journal of Chemistry. 39 (1), 361-368 (2015).</li><li>Guo, P., Zhang, G., Yu, J., Li, H., Zhao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+synthesis,+magnetic+and+photocatalytic+properties+of+hollow+spheres+and+colloidal+nanocrystal+clusters+of+manganese+ferrite.">Controlled synthesis, magnetic and photocatalytic properties of hollow spheres and colloidal nanocrystal clusters of manganese ferrite.</a> Colloids and Surfaces A: Physicochemical and Engineering Aspects. 395, 168-174 (2012).</li><li>Pardo, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis,+characterization,+and+evaluation+of+superparamagnetic+doped+ferrites+as+potential+therapeutic+nanotools.">Synthesis, characterization, and evaluation of superparamagnetic doped ferrites as potential therapeutic nanotools.</a> Chemistry of Materials. 32 (6), 2220-2231 (2020).</li><li>Xiao, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Libraries+of+uniform+magnetic+multicore+nanoparticles+with+tunable+dimensions+for+biomedical+and+photonic+applications.">Libraries of uniform magnetic multicore nanoparticles with tunable dimensions for biomedical and photonic applications.</a> ACS Applied Materials &amp; Interfaces. 12 (37), 41932-41941 (2020).</li><li>Choi, Y. S., Young Yoon, H., Sung Lee, J., Hua Wu, J., Keun Kim, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+magnetic+properties+of+size-tunable+Mn+x+Fe3&#8722;x+O4+ferrite+nanoclusters.">Synthesis and magnetic properties of size-tunable Mn x Fe3&#8722;x O4 ferrite nanoclusters.</a> Journal of Applied Physics. 115 (17), (2014).</li><li>Creixell, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+grafting+method+on+the+colloidal+stability+and+in+vitro+cytotoxicity+of+carboxymethyl+dextran+coated+magnetic+nanoparticles.">The effect of grafting method on the colloidal stability and in vitro cytotoxicity of carboxymethyl dextran coated magnetic nanoparticles.</a> Journal of Materials Chemistry. 20 (39), 8539-8547 (2010).</li><li>Latorre, M., Rinaldi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applications+of+magnetic+nanoparticles+in+medicine:+magnetic+fluid+hyperthermia.">Applications of magnetic nanoparticles in medicine: magnetic fluid hyperthermia.</a> Puerto Rico Health Sciences Journal. 28 (3), (2009).</li><li>Yeap, S. 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The authors have nothing to disclose.

This work demonstrates a modified polyol synthesis of manganese ferrite nanocrystals clustered together into uniform nanoscale aggregates29. In this synthesis, iron(III) chloride and manganese(II) chloride undergo a forced hydrolysis reaction and reduction, forming molecular MnxFe3-xO4. These ferrite molecules form primary nanocrystals under the high temperature and high pressure in the reactors, ultimately assembling into spherical aggregates termed her...

The inclusion of manganese as a dopant in an iron oxide lattice can, under the appropriate conditions, increase the material&#39;s magnetization at high applied fields as compared to pure iron oxides. As a result, manganese ferrite (MnxFe3-xO4) nanoparticles are highly desirable magnetic nanomaterials due to their high saturation magnetization, strong response to external fields, and low cytotoxicity1,2,3,4,5. Both single domain nanocrystals as well as clusters of these nanocrystals, termed multidomain particles, have been investigated in diverse biomedical applications, including drug delivery, magnetic hyperthermia for cancer treatment, and magnetic resonance imaging (MRI)6,7,8. For example, the Hyeon group in 2017 used single domain manganese ferrite nanoparticles as a Fenton catalyst to induce cancer hypoxia and exploited the material&#39;s T2contrast for MRI tracking9. It is surprising in light of these and other positive studies of ferrite materials that there are few in vivo demonstrations as compared to pure iron oxide (Fe3O4) nanomaterials, and no reported applications in humans9,10.
One immense challenge faced in translating the features of ferrite nanomaterials into the clinic is the generation of uniform, non-aggregating, nanoscale clusters11,12,13,14. While conventional synthetic approaches to monodomain nanocrystals are well developed, multidomain clusters of the type of interest in this work are not easily produced in a uniform and controlled fashion15,16. Additionally, ferrite composition is usually non-stoichiometric and not simply related to the starting concentration of the precursors and this can further obscure systematic structure-function characterization of these materials9,12,13,17. Here, we address these issues by demonstrating a synthetic approach that yields independent control over both the cluster dimension and composition of manganese ferrite nanomaterials.
This work also provides a means to overcome the poor colloidal stability of ferrite nanomaterials18,19,20. Magnetic nanoparticles are generally prone to aggregation due to strong particle-particle attraction; ferrites suffer more from this problem as their larger net magnetization amplifies particle aggregation. In relevant biological media, these materials yield large enough aggregates that the materials rapidly collect, thereby limiting their routes of exposure to animals or people20,21,22. Hilt et al. found another consequence of particle-particle aggregation in their study of magnetothermal heating and dye degradation23. At slightly higher particle concentrations, or increased time of exposure to the field, the effectiveness of the materials was reduced as materials aggregated over time and the active particle surface areas decreased. These and other applications would benefit from cluster surfaces designed to provide steric barriers that precluded particle-particle interactions24,25.
Here we report a synthetic approach to synthesize manganese ferrite clusters (MFCs) with controllable dimensions and composition. These multidomain particles consist of an assembly of primary manganese ferrite nanocrystals that are hard aggregated; the close association of the primary nanocrystals enhances their magnetic properties and provides for an overall cluster size, 50-300 nm, well matched to the optimum dimensions for a nanomedicine. By changing the amount of water and manganese chloride precursor, we can independently control the overall diameter and composition. The method utilizes simple and efficient one-pot hydrothermal reactions that allow for frequent experimentation and material optimization. These MFCs can be easily purified into a concentrated product solution, which is further modified by sulfonated polymers that impart colloidal stability. Their tunability, uniformity, and solution phase stability are all features of great value in applications of nanomaterials in biomedical and environmental engineering.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.1 Micron Vaccum Filtration Filter</td>
			<td>Thermo Fisher Scientific</td>
			<td>NC9902431</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>2-Acrylamido-2-methylpropane sulfonic acid (AMPS, 99%)</td>
			<td>Sigma-Aldrich</td>
			<td>282731-250G</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media</td>
		</tr>
		<tr>
			<td>2,2&#8242;-Azobis(2-methylpropionitrile) (AIBN)</td>
			<td>Sigma-Aldrich</td>
			<td>441090-100G</td>
			<td>reagent used in copolymer making as the free ridical generator</td>
		</tr>
		<tr>
			<td>4-Morpholineethanesulfonic acid, 2-(N-Morpholino)ethanesulfonic acid (MES)</td>
			<td>Sigma-Aldrich</td>
			<td>M3671-250G</td>
			<td>acidic buffer used to stabilize nanocluster surface coating process</td>
		</tr>
		<tr>
			<td>Acrylic acid</td>
			<td>Sigma-Aldrich</td>
			<td>147230-100G</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media; anhydrous, contains 200 ppm MEHQ as inhibitor, 99%</td>
		</tr>
		<tr>
			<td>Analytical Balance</td>
			<td>Avantor</td>
			<td>VWR-205AC</td>
			<td>used to weigh out solid chemical reagents for use in synthesis and dilution</td>
		</tr>
		<tr>
			<td>Digital Sonifier and Probe</td>
			<td>Branson</td>
			<td>B450</td>
			<td>used to sonicate nanocluster solution during surface coating to break up aggregates</td>
		</tr>
		<tr>
			<td>Dopamine hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>H8502-25G</td>
			<td>used in surface coating for ligand exchange reaction</td>
		</tr>
		<tr>
			<td>Ethylene glycol (anhydrous, 99.8%)</td>
			<td>Sigma-Aldrich</td>
			<td>324558-2L</td>
			<td>reagent used as solvent in hydrothermal synthesis of nanoclusters</td>
		</tr>
		<tr>
			<td>Glass Vials (20mL)</td>
			<td>Premium Vials</td>
			<td>B1015</td>
			<td>container for nanocluster solution during washing and surface coating as well as polymer solutions</td>
		</tr>
		<tr>
			<td>Graduated Beaker (100mL)</td>
			<td>Corning</td>
			<td>1000-100</td>
			<td>container for mixing of solid and liquid reagents during hydrothermal synthesis (to be transferred into autoclave reactor before oven)</td>
		</tr>
		<tr>
			<td>Handheld Magnet</td>
			<td>MSC Industrial Supply, Inc.</td>
			<td>92673904</td>
			<td>1/2&#34; Long x 1/2&#34; Wide x 1/8&#34; High, 5 Poles, Rectangular Neodymium Magnet low strength magnet used to precipitate nanoclusters from solution (field strength is increased with steel wool when needed)</td>
		</tr>
		<tr>
			<td>Hydrochloric acid (ACS grade, 37%)</td>
			<td>Fisher Scientific</td>
			<td>7647-01-0</td>
			<td>for removing leftover nanocluster debris and cleaning autoclave reactors for next use</td>
		</tr>
		<tr>
			<td>Hydrothermal Autoclave Reactor</td>
			<td>Toption</td>
			<td>TOPT-HP500</td>
			<td>container for finished reagent mixture to withstand high temperature and pressure created by the oven in hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Iron(III) Chloride Hexahydrate (FeCl3&#183;6H2O, ACS reagent, 97%)</td>
			<td>ACS</td>
			<td>236489-500G</td>
			<td>reagent used in synthesis of nanoclusters as source of iron (III) that becomes iron (II) in finished nanocluster product (keep dry and weigh out quickly to avoid water contamination)</td>
		</tr>
		<tr>
			<td>Labware Washer Brushes</td>
			<td>Fisher Scientific</td>
			<td>13-641-708</td>
			<td>used to wash and clean glassware before synthesis</td>
		</tr>
		<tr>
			<td>Magnetic Stir Plate</td>
			<td>Thermo Fisher Scientific</td>
			<td>50093538</td>
			<td>for mixing of solid and liquid reagents during hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Manganese chloride tetrahydrate (MnCl2&#183;4H2O, 99.0%, crystals, ACS)</td>
			<td>Sigma-Aldrich</td>
			<td>1375127-2G</td>
			<td>reagent used in synthesis of nanoclusters as source of manganese</td>
		</tr>
		<tr>
			<td>Micropipette (100-1000&#956;L)</td>
			<td>Thermo Fisher Scientific</td>
			<td>FF-1000</td>
			<td>for transferring liquid reagents such as water and manganese chloride</td>
		</tr>
		<tr>
			<td>N-(3-Dimethylaminopropyl)-N&#8242;-ethylcarbodiimide hydrochloride (EDC)</td>
			<td>Sigma-Aldrich</td>
			<td>25952-53-8</td>
			<td>used in surface coating to assist in ligand exchange of copolymer (keep bulk chemical in freezer and diluted solution in refrigerator)</td>
		</tr>
		<tr>
			<td>N,N-Dimethylformamide (DMF)</td>
			<td>Sigma-Aldrich</td>
			<td>227056-2L</td>
			<td>reagent used in copolymer making as the solvent</td>
		</tr>
		<tr>
			<td>Polyacrylic acid sodium salt (PAA, Mw~6,000)</td>
			<td>PolyScience Inc.</td>
			<td>06567-250</td>
			<td>reagent used in hydrothermal synthesis to initially coat the nanoclusters (eventually replaced in surface coating step)</td>
		</tr>
		<tr>
			<td>Poly(ethylene glycol) methyl ether acrylate</td>
			<td>Sigma-Aldrich</td>
			<td>454990-250ML</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media; average Mn 480, contains 100 ppm BHT as inhibitor, 100 ppm MEHQ as inhibitor</td>
		</tr>
		<tr>
			<td>Reagents Acetone, 4L, ACS Reagent</td>
			<td>Cole-Parmer</td>
			<td>UX-78920-66</td>
			<td>used as solvent to precipitate nanoclusters during washing</td>
		</tr>
		<tr>
			<td>Single Channel Pipette, Adjustable 1-10 mL</td>
			<td>Eppendorf</td>
			<td>3123000080</td>
			<td>for transferring ethylene glycol and other liquids</td>
		</tr>
		<tr>
			<td>Steel Wool</td>
			<td>Lowe&#39;s</td>
			<td>788470</td>
			<td>used to increase the magnetic field strength in the vial to aid in precipitation of nanoclusters for washing and surface coating</td>
		</tr>
		<tr>
			<td>Stirring Bar</td>
			<td>Thomas Scientific</td>
			<td>8608S92</td>
			<td>for mixing of solid and liquid reagents during hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Table Clamp</td>
			<td>Grainger</td>
			<td>29YW53</td>
			<td>for tight sealing of autoclave reactor to withstand high pressure of oven during hyrothermal synthesis</td>
		</tr>
		<tr>
			<td>Urea (ACS reagent, 99.0%)</td>
			<td>Sigma-Aldrich</td>
			<td>U5128-500G</td>
			<td>reagent used in hydrothermal synthesis to create a basic solution</td>
		</tr>
		<tr>
			<td>Vaccum Filtration Bottle Tops</td>
			<td>Thermo Fisher Scientific</td>
			<td>596-3320</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>Vacuum Controller V-850</td>
			<td>Buchi</td>
			<td>BU-V850</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>Vacuum Oven</td>
			<td>Fisher Scientific</td>
			<td>13-262-51</td>
			<td>used to create high temperature and pressure needed for nanocluster formation in hydrothermal synthesis</td>
		</tr>
	</tbody>
</table>

stable aqueous suspensions of manganese ferrite clusters with tunable nanoscale dimension and composition

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

After hydrothermal treatment, the reaction mixture turns into a viscous black dispersion as can be seen in Figure 1. What results after purification is a highly concentrated MFC solution that behaves like a ferrofluid. The fluid in the vial responds within seconds when placed near a handheld magnet (&#60;0.5 T), forming a macroscopic black mass that can be moved around as the magnet is placed at different locations.
This synthesis yields products whose dimension a...

Watch this Scientific Journal Video about Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition at JoVE.com

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

We report a one-pot hydrothermal synthesis of manganese ferrite clusters (MFCs) that offers independent control over material dimension and composition. Magnetic separation allows rapid purification while surface functionalization using sulfonated polymers ensures the materials are non-aggregating in biologically relevant medium. The resulting products are well positioned for biomedical applications.

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse ...

In this video, we present the synthesis, of super paramagnetic manganese ferrite nano clusters. We report a one pot hydrothermal synthesis of manganese ferrite clusters or MFCs that offers independent control over both primary nanocrystal and cluster dimension, as well as the iron to manganese ratio. Magnetic separation allows for rapid sample purification while service functionalization using a sulfonated polymer ensures that the materials are non-aggregating, even in biologically relevant aqueous solutions.The resulting products are well positioned for applications in biotechnology and medicine. Wash and thoroughly dry all glassware to be used in the synthesis. The amount of water in the synthesis impacts the dimensions of the MFCs.So it's crucial to ensure the glassware has no residual water in it. To wash the glassware, rinse with water and detergent and scrub with a FLAS brush to remove debris. Thoroughly rinse to remove all detergent and finish with the rinse of deionized water.Rinse the polyphenol lined reactors with 37%hydrochloric acid to remove any debris from previous use. To do this, place the reactors and their caps in a large beaker and fill with hydrochloric acid until the reactors are completely submerged. Let this sit for 30 minutes before pouring out the hydrochloric acid.Continuously rinse the beaker with the reactors with water for one to two minutes, then place the reactors in the oven to dry. Use an automatic pipette to transfer 20 milliliters of ethylene glyco into a 50 milliliter beaker with a magnetic stir bar. Weight out the required amount of iron chloride to achieve a final concentration of 1.3 millimolar and add it to the beaker.Put the beaker on a stir plate and turn it on at 480 RPM to begin continuous stirring of the beaker. Weigh 250 milligrams of polyacrylic acid and add it to the beaker. After the addition of PAA, the solution becomes opaque and slightly lighter in color.Weigh 1.2 grams of Urea and add it to the beaker. Using a pipette, add 0.7 millimolar manganese chloride to the beaker. Finally, using the pipette, add the required amount of ultra pure water to the beaker.Let the solution stir for thirty minutes and notice the color change. It'll present as a translucent dark orange color. Transfer the reaction mixture into the PPL reactor.Note that after the solution has stirred, some solids may have accumulated on the sides of the beaker. Use a magnet to drag the stir bar around the walls of the beaker to ensure any solids that have accumulated on the sides are dispersed into the reaction solution. Once the solution is mixed and ready, transfer it into the 50 milliliter PPL lined reactor.Use a clamp and lever to seal the reactor in the stainless steel autoclave as tightly as possible. Clamp the reactor vessel to a stable surface and using a rod, insert it into the cap as a lever, push the reactor to seal. Note that the sealed reactor should not be able to be opened by hand.This is crucial as the high pressure environment of the oven requires a tight seal on the reactor. Place a reactor into an oven for 20 hours at 215 degrees Celsius. After the hydrothermal reaction is done, remove the reactor from the oven and allow it to cool down to room temperature.The pressure of the oven will enable the reactor to be opened by hand. Note that at this point, the reactor will contain the MFC product dispersed in ethylene glycol with other impurities, such as unreacted polymer. And will be opaque black solution.The product isolated in the following steps. Place 200 milligrams of steel wool into a glass vial. Fill the glass vial halfway with the reaction mixture from the reactor.Fill the rest of the vial with acetone and shake well. Note that the steel wool increases the magnetic field strength in the vial and will help magnetic separation of the nano clusters from solution. Place the vial on a magnet for magnetic collection to occur.The result will be a translucent solution with precipitate at the bottom. Pour off the supernatant solution while the MFCs are magnetically trapped by the steel wool by holding the magnet to the bottom of the vial while pouring. Ethylene glycol will mostly be removed in this step.Start washing with the low ratio of acetone to water and increase the ratio in subsequent washes until pure. Do this three to four times. Remove the vial from the magnet and fill it with water.Shake well to dissolve the MFCs. Now the product will be fully dispersed in water. Repeat the previous two steps several times until the aqueous solution of the MFCs produces no bubbles when shaken.The result will be a dark opaque ferrofluid that will respond strongly to magnets. In order to keep our clusters stable, we modify them with a co-polymer, PAA-co-AMPS-co-PEG, which provides both steric and electrostatic repulsion. The sulfonate group of the AMPS units will provide charge stabilization while the PEG unit will stericly hinder the inter cluster aggregation.Overall, the modified clusters will remain stable even in various types of harsh conditions. Combine 10 milliliters of purified nanoparticles in a 20 milliliter vial, with 10 milliliters of saturated Nitra dopamine solution. Wait for five minutes.Wash the Nitra dopamine coated MFCs using magnetic separation. Pour out the pale yellow supernatant. Add water and shake vigorously.Then pour out water using the magnet to retain the product. Repeat this washing several times, leaving the dark brown collection in the vial. Mix one milliliter of EDC solution, one milliliter of MES buffer, and three milliliters of polymer solution.Lightly stir by swirling the mixture and let it sit for approximately five minutes. It should be a clear and colorless solution when fully combined. Add this mixture to the MFC collection and place the vial in an ice bath.Lower the probe sonicator into the solution and then turn it on. After a five minute sonication treatment, add roughly five milliliters of ultra pure water to the vial while the sonicator is still running. Continue monitoring the vessel to ensure that no product spills.Maintain the ice in the ice water mixture, as some of the initial ice will melt due to the intensity and heat of the sonication. Allow the mixture to sonicate for an additional 25 minutes for a total of 30 minutes. Place the vial on top of a magnet to separate the MFCs and pour out the supernatant solution.Wash the modified MFCs with deionized water several times. Fill the vial with the MFCs with ultra pure water. Pipette this fluid into a vacuum filtration system with a 0.1 micron polyether sulfate membrane filter to remove any irreversibly aggregated MFCs.Make sure to flush the walls of the funnel to minimize any loss of product. Vacuum filter the solution. Repeat this process two to three times.The result will be a purified aqueous solution of mono disperse MFCs. MFCs isolated when the magnetic separation method have higher mono dispersity than those separated with ultracentrifugation, as shown here. Here, we see TEM images of purified nano clusters, in order of increasing average cluster diameter.Denoted as DC.The amount of water added in the initial reaction mixture determines the diameter of the nano clusters. Adding more water in the reaction results in nano clusters with smaller diameters, while less water increases their diameters. In this way, the experimenter has control over the size of the nano cluster product.Here we see TEM images of nano clusters in order of increasing manganese to iron molar ratio. The ratio of manganese to iron precursors in the initial reaction mixture determines the molar ratio of the metals in the cluster product. Increasing the manganese to iron ratio in the synthesis will increase this ratio in the clusters, and vice versa.In contrast the following TEM images depict samples with irregular morphologies. As shown in the left image, the out of shape spilled looking cluster was produced with the exclusion of any additional water. This hinders the dynamic assembly of the primary nano crystals that have yet to form clusters.The sample in the image on the right had insufficient reaction time, which was not enough for primary nano crystal growth and cluster ripening. These poor results demonstrate that an appropriate amount of the reactant as well as reaction time is necessary to achieve consistently successful results. Here, we place a sample of the original PAA coded clusters in PBS buffer on the left.On the right, we do the same with an equivalent amount of the modified PAA co-AMPS-co-PEG coded clusters. Notice the fast aggregation of the PAA coded clusters, while the modified clusters remain stable for a long time. This suggests the improved colloidal stability as a result of the copolymer coding.In conclusion, our synthesis allows for the quick and efficient production of manganese ferrite clusters. The synthesis creates independently tunable cluster dimension and composition by simply controlling the addition of water and manganese to iron precursor ratio. We can easily modify this method to achieve different but predictable magnetic nanomaterials.Further, the magnetic separation and service functionalization techniques achieve high mono dispersity and strong stability in biological media, respectively. Our method allows for greater accessibility in the clusters production and widespread application across a variety of fields.

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JoVE Journal

Chemistry

4.1K Views.  Brown University. In this video, we present the synthesis, of super paramagnetic manganese ferrite nano clusters. We report a one pot hydrothermal synthesis of manganese ferrite clusters or MFCs that offers independent control over both primary nanocrystal and cluster dimension, as well as the iron to manganese ratio. Magnetic separation allows for rapid sample purification while service functionalization using a sulfonated polymer ensures that the materials are non-aggregating, even in biologically relevant a...