![]() ![]() NanocrystalsHexagonal nanolpatesMonodisperse nanocrystalsĢ.5–4.5 12,000 30 (side length) 100 175 (DLS) Hydrothermal synthesis Hydrothermal synthesis Hydrothermal synthesis Hydrothermal synthesis Hydrothermal synthesis The viable distribution of vacancy sites ideal for the base structure of NiAs was observed to describe the structure of Fe 9S 10 (Elliot, 2010). It has been established that the Fe 7S 8 structure is a hexagonal supercell (Fleet, 1971). In addition, the cubic structure of Fe 3S 4 forms a closely packed array of S molecules linked by smaller Fe units ( Figure 1D). Fe 3S 4 has an inverse spinel structure in which 8 Fe atoms are located at the tetrahedral A-sites and 16 Fe atoms are located at the B-sites of the octahedron. ![]() In addition, FeS 2 exhibits chirality through absorbed organic molecules. The structure of FeS 2 is similar to that of NaCl in which S 2− is located at the center of a cube. The structure of Fe 2S 2 is closed to FeS. To assess the effects of van der Waals forces resulting from the S atoms, sheets including Fe are stacked along the C-axis. In addition, Fe-Fe bonding is substantial in FeS. A single iron atom is coordinated to four equidistant sulfur atoms. FeS possesses a tetragonal layered structure in which the iron atoms are linked through tetrahedral coordination to four equidistant sulfur atoms. Reported crystal structures of iron sulfide are displayed in Figure 1 (Fleet, 1971 Argueta-Figueroa et al., 2017). Hexagonal Fe 9S 11 is related to the Fe 1−xS phase (Rickard and Luther, 2007). FeS 2m differs from FeS 2p as an orthorhombic metastable iron (II) disulfide, whilst Fe 3S 4 is a cubic metastable Fe (II) Fe (III) sulfide. FeS 2p forms stable iron (II) disulfides with cubic structures. For Fe 1−xS, a monoclinic hexagonal is present. FeS naturally has a tetragonal structure, with each iron atom coordinated to four sulfurs. The content of iron within a biomaterial therefore influences its phase, shape, and physical and chemical properties. Solid phases of iron sulfides principally comprise FeS (mackinawite), Fe 1−xS (pyrrhotite), FeS 2p (pyrite), FeS 2m (marcasite), Fe 3S 4 (greigite), and Fe 9S 11 (smythite). This will provide a comprehensive understanding of iron sulfide nanomaterials and illustrate their considerable potential as novel multifunctional biomaterials in biomedical applications. ![]() Herein, we will summarize the types, synthesis and properties of iron sulfide nanomaterials and emphasize their applications in biomedical and medical fields. Therefore, it is anticipated that iron sulfide nanomaterials will display multiple functionalities and they have great potential in biomedical applications. Importantly, iron-sulfur clusters are important cofactors in many enzymes which serve as active centers for electron transfer in catalytic processes and respiratory chain reactions (Qi and Cowan, 2011). ![]() The band gap in iron sulfide is smaller than that of iron oxide, leading to the former having more appropriate electron transfer and conductivity (Wadia et al., 2009 Jin et al., 2017 Zhang et al., 2018). In addition, the phases of iron sulfide in nature include mackinawite (FeS), pyrrhotite (Fe 1−xS), pyrite (FeS 2), and greigite (Fe 3S 4), etc., which exhibit more variability than iron oxide containing only Fe 2O 3 and Fe 3O 4. Since O and S are congeneric elements, iron sulfide demonstrates similar physiochemical properties as iron oxide (Fu et al., 2019). However, iron sulfide nanomaterials have not been comprehensively studied or used in the biomedical fields. Currently, the majority of iron-based nanomaterials are iron oxide which possess excellent supraparamagnetic properties, with catalytic activity mimicking that of oxido-reductases, including peroxidase, catalase, superoxide dismutase, and oxidase (Gao et al., 2007 Liang and Yan, 2019). In addition, recent studies have revealed that these nanomaterials have intrinsic enzyme-like properties (Gao et al., 2007 Xie et al., 2012 Xu et al., 2018), an important form of nanozyme representing a new generation of artificial enzyme (Wei and Wang, 2013 Dong et al., 2019 Liang and Yan, 2019). In particular, due to their multiple functionality and excellent biocompatibility, iron-based nanomaterials are frequently used in the biomedical field, such as bioseparation, biosensors, magnetic resonance imaging (MRI), tumor hyperthermia, and drug delivery (Chen and Gu, 2017). With the development of nanotechnology (Li et al., 2019), nanomaterials have become a major resource for the development of novel therapeutic medicines and technologies designed to improve human health and the quality of life (Zhang and Webster, 2009 Esmaeili et al., 2020 Wang et al., 2020). ![]()
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