LITMIR.BIZ

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In addition, the large internal surface area and pore capacity of mesoporous materials allow a high loading of cargo molecules and also prevent them from escaping into water easily by dissolving in an aqueous environment (Jafari et al. 2019). These advantages enhance the effectiveness of the MSNP‐based delivery system and allow a specific amount of drugs to reach their therapeutic target (Li et al. 2012).

      1.2.1.3 Superparamagnetic Nanoparticles

      Among the inorganic nanoparticles, superparamagnetic nanoparticles (Figure 1.1c) are considered the most unique nanoparticles due to their strong magnetic properties. These nanoparticles were for the first time used in the late 1980s for biomedical applications (Stark et al. 1988). Usually, the core of these nanoparticles consists of metal molecules of nickel, cobalt, or iron oxide (Fe₃O₄ magnetite, which is the most commonly used metal). As mentioned above, superparamagnetic nanoparticles are considered most unique because the surface of these nanoparticles can be easily modified by coating the core with various organic polymers like dextran, starch, alginate, inorganic metals, oxides (silica, alumina), etc. (Núñez et al. 2018).

      Superparamagnetic nanoparticles can be promisingly used for the diagnosis of various diseases including cancer (tumors) by conjugating with various bioactive ligands (Anderson et al. 2019). To date, a number of approaches have been developed for the fabrication of superparamagnetic nanoparticles which have the potential ability to distinguish cancerous tissue from healthy tissue. In addition, these nanoparticles can be used for magnetic resonance imaging (MRI) of tumor tissue, cell labeling, and drug delivery in different diseases (Núñez et al. 2018; Anderson et al. 2019).

      1.2.1.4 Quantum Dots

Quantum dots (Figure 1.1d) are the class of semiconductor nanoparticles with unique photo‐physical properties. Usually, quantum dots have a core/shell structure composed of molecules of various metals like technetium, cadmium selenide, zinc, indium, tantalum, etc. (Medintz et al. 2005; Wang et al. 2019). The most commonly used, commercially available quantum dots contain a cadmium selenide core covered with a zinc‐sulfide shell. The core‐shell complex is generally encapsulated in a coordinating ligand and an amphiphilic polymer (Gao et al. 2004). Due to unique optical properties, quantum dots have been used as dominant classes of fluorescent imaging probes for various biomedical applications (Núñez et al. 2018).

      1.2.1.5 Graphene

      Graphene is an atom‐thick monolayer of carbon atoms arranged in a two‐dimensional honeycomb structure (Figure 1.1e) (Novoselov et al. 2004). Generally, graphene has been extensively used for a wide array of applications in many fields such as quantum physics, nanoelectronic devices, transparent conductors, energy research, catalysis, etc. (Wang et al. 2011; Huang et al. 2012). However, according to recent technological advancements graphene, graphene oxide, and reduced graphene oxide have shown promising applications in the biomedical field and hence have attracted significant interest worldwide (Gonzalez‐Rodriguez et al. 2019; Yang et al. 2019). Due to its excellent physicochemical and mechanical properties, single‐layered graphene has been widely utilized as a novel nanocarrier for drug and gene delivery in different diseases (Núñez et al. 2018).

      1.2.1.6 Carbon Nanotubes (CNTs)

      CNTs are cylindrical nanomaterials that consist of rolled‐up sheets of graphene (single‐layer carbon atoms). Depending on their structure CNTs can be divided into two types, namely single‐walled carbon nanotubes (SWCNTs) (Figure 1.1f), which usually have diameter of less than 1 nm, and multi‐walled carbon nanotubes (MWCNTs) (Figure 1.1g), which are composed of many concentrically interlinked nanotubes, usually having a diameter size of more than 100 nm (Hsu and Luo 2019). CNTs are considered as one of the stiffest and strongest fibers having novel exceptional characteristics and a unique physicochemical framework, which makes them suitable candidates for efficient delivery of different therapeutic drugs/molecules for various biomedical applications (Vengurlekar and Chaturvedi 2019). Figure 1.1 represents the schematic illustration of various inorganic nanomaterials.

      1.2.2 Organic Nanomaterials

      1.2.2.1 Polymeric Nanoparticles

Polymeric nanoparticles (Figure 1.2a,b) are colloidal solid particles having a size in the range of 10 nm–1 μm. Based on the preparation method, polymeric nanoparticles can be classified into two types of structures: nanocapsule (Figure 1.2a) and nanosphere (Figure 1.2b). Among these, nanospheres consist of a matrix system which facilitates uniform dispersion of the drug. However, in the case of nanocapsules, the drug is only embedded in a cavity and the cavity is surrounded by a polymeric membrane (Sharma 2019). Among the various organic nanomaterials, polymeric nanoparticles have attracted huge attention over the last few years due to their unique properties and behaviors resulting from their small size. As reported in many studies, these nanoparticles demonstrated potential applications in biomedicine particularly in diagnostics and drug delivery. Polymeric nanoparticles are preferably used as a nanocarrier for the conjugation of various drugs, natural polymers (e.g. natural polymers like chitosan, gelatin, alginate, and albumen), and synthetic polymers (Zhang et al. 2013a,b). Further, they showed significant benefits in treatment because of controlled release of the drug, their ability to combine both therapy and imaging (theranostics), protection of drug molecules due to conjugation, and their target‐specific drug delivery (Crucho and Barros 2017).

Figure 1.2 Schematic representation of various organic nanomaterials.

      1.2.2.2 Polymeric Micelles

Polymeric micelle (Figure 1.2c) is the class of organic nanomaterials usually formed by the spontaneous arrangement of amphiphilic block copolymers in aqueous solutions (Kulthe et al. 2012). Structurally these nanomaterials are composed of the hydrophobic core and hydrophilic shell, which facilitates the loading of various hydrophobic drugs like camptothecin, docetaxel, paclitaxel, etc. into the core to be used as nanocarriers (Singh et al. 2019). The encapsulation of drugs in polymeric micelles enhances their solubility. Various novel properties of polymeric micelles, including their small size, make them promising nanocarriers in drug delivery. Polymeric micelle‐mediated drug delivery showed many advantages like easy penetration, target‐specific drug delivery, narrow distribution to avoid fast renal excretion, etc. Moreover, polymeric micelles can also be conjugated with targeting ligands which facilitates their uptake by specific cells, thus reducing off‐target side effects. Polymeric micelles can be synthesized using two different approaches: (i) convenient solvent‐based direct dissolution of polymer followed by dialysis process; or (ii) precipitation of one block by adding a solvent (Patra et al. 2018).

      1.2.2.3 Liposomes

The word liposome (Figure 1.2d) has been derived from the two Greek words: lipo (“fat”) and soma (“body”), and was described for the first time by

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