Magnetic Iron Oxide Nanoparticle (IONP) Synthesis to Applications: Present and Future

Abstract

Iron oxides are chemical compounds which have different polymorphic forms, including γ-Fe₂O₃ (maghemite), Fe₃O₄ (magnetite), and FeO (wustite). Among them, the most studied are γ-Fe₂O₃ and Fe₃O₄, as they possess extraordinary properties at the nanoscale (such as super paramagnetism, high specific surface area, biocompatible etc.), because at this size scale, the quantum effects affect matter behavior and optical, electrical and magnetic properties. Therefore, in the nanoscale, these materials become ideal for surface functionalization and modification in various applications such as separation techniques, magnetic sorting (cells and other biomolecules etc.), drug delivery, cancer hyperthermia, sensing etc., and also for increased surface area-to-volume ratio, which allows for excellent dispersibility in the solution form. The current methods used are partially and passively mixed reactants, and, thus, every reaction has a different proportion of all factors which causes further difficulties in reproducibility. Direct active and complete mixing and automated approaches could be solutions to this size- and shape-controlled synthesis, playing a key role in its exploitation for scientific or technological purposes. An ideal synthesis method should be able to allow reliable adjustment of parameters and control over the following: fluctuation in temperature; pH, stirring rate; particle distribution; size control; concentration; and control over nanoparticle shape and composition i.e., crystallinity, purity, and rapid screening. Iron oxide nanoparticle (IONP)-based available clinical applications are RNA/DNA extraction and detection of infectious bacteria and viruses. Such technologies are important at POC (point of care) diagnosis. IONPs can play a key role in these perspectives. Although there are various methods for synthesis of IONPs, one of the most crucial goals is to control size and properties with high reproducibility to accomplish successful applications. Using multiple characterization techniques to identify and confirm the oxide phase of iron can provide better characterization capability. It is very important to understand the in-depth IONP formation mechanism, enabling better control over parameters and overall reaction and, by extension, properties of IONPs. This work provides an in-depth overview of different properties, synthesis methods, and mechanisms of iron oxide nanoparticles (IONPs) formation, and the diverse range of their applications. Different characterization factors and strategies to confirm phase purity in the IONP synthesis field are reviewed. First, properties of IONPs and various synthesis routes with their merits and demerits are described. We also describe different synthesis strategies and formation mechanisms for IONPs such as for: wustite (FeO), hematite (α-Fe₂O₃), maghemite (ɤ-Fe₂O₃) and magnetite (Fe₃O₄). We also describe characterization of these nanoparticles and various applications in detail. In conclusion, we present a detailed overview on the properties, size-controlled synthesis, formation mechanisms and applications of IONPs.

Keywords: biomedical; formation mechanisms; iron oxide nanoparticles (IONPs); reproducible.

Figure 1

Various applications of iron oxide nanoparticles (IONPs).

Figure 2

Challenges and key points in reproducible synthesis of nanoparticles.

Figure 3

(a,b) TEM of FeO nanoparticles synthesized by thermal decomposition, (c) particle size distribution plot, (d) SAED pattern. Obtained permission from Ref. [53]. Copyright 2010 American Chemical society.

Figure 4

TEM micrographs: (a) spherical shaped and (b) cubical shaped. Obtained permission from Ref. [55]. Copyright 2011 American Chemical society.

Figure 5

(a) XRD pattern of FeO nanoparticles: (b) Mössbauer spectrum of FeO nanoparticles at room temperature. Obtained permission from Ref. [54]. Copyright 2008 John Wiley and Sons.

Figure 6

(a,b)TEM images of α-Fe₂O₃ nanoparticles calcinated at 450 °C, (c) thermogravimetric analysis of precursors in air. Obtained permission from Ref. [59]. Copyright 2009 Elsevier.

Figure 7

(A,B) TEM and AFM images of typical rhombohedral shape of α-Fe₂O₃ nanoparticles, respectively; (C) size distribution obtained by dynamic light scattering(DLS). Obtained permission from Ref. [60]. Copyright 2012 Elsevier.

Figure 8

XRD pattern of iron oxide nanoparticles (top: 30 °C and bottom: 80 °C); γ-Fe₂O₃ phase indicated by black dots. Obtained permission from Ref. [62]. Copyright 2015 Elsevier.

Figure 9

TEM: γ-Fe₂O₃ nanoparticles, (a,b), (c). Obtained permission from Ref. [67]. Copyright 2015 Elsevier, Obtained permission from Ref. [68]. Copyright 2014 Hindawi Publishing Corporation.

Figure 10

Fe₃O₄ nanoparticles synthesized by ascorbic acid mediated reduction of Fe(acac)₃, (a) without water, (b) with water, (c) graphene–Fe₃O₄ nanoparticles [22,25,26,27].

Figure 11

Droplet of ascorbic acid solution.

Figure 12

Magnetic separation process. (I) Tagging of desired biological entity with IONPs (•); (II) Separation of desired entity-tagged nanoparticles by fluid-based magnetic process (◦).