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The word “nano” is derived from the Greek word which means “dwarf.” One nanometer is the 1 billionth or 10⁻⁹ part of a meter. The nano‐size range holds so much interest because in this range materials can have diverse and enhanced properties compared with the same material at a larger (bulk) size (Gholami‐Shabani et al. 2015; Dudefoi et al. 2018). Materials in the nano‐scale differ significantly from other materials due to the following two major principal reasons: physical effects such as expanded surface area and phenomena are based on “quantum effects” (Gholami‐Shabani et al. 2016). These properties can enhance the reactivity, durability, and electrical features and in vivo behavior of nanomaterials.

      Due to these unique properties of nanomaterials, modern nanotechnology is emerging as potential branch of science that can revolutionize various fields, including biomedicine. Looking at the recent advances in the field of nanotechnology it can be observed that nanotechnology influences almost every facet of everyday life from security to medicine. Nanotechnology and its medical applications are usually seen as having a wide potential to cause benefits to various areas of investigation and applications. Currently, nanotechnology is providing completely novel concepts and approaches in various fields of biomedicine such as diagnosis, drug delivery, and treatment of a wide range of diseases including various serious and life‐threatening diseases like cancer, neurodegenerative disorders, cardiovascular diseases, etc.

      To date, a variety of nanomaterials have been investigated which play a crucial role in the diagnosis and management of different diseases as mentioned. The nanomaterials which are used in medicine are termed as “nanomedicine.” The concept of nanomedicine was first put forward in 1993 by Robert A. Freitas, Jr. Nanomedicine is considered the science of preventing, diagnosing, and treating disease using nanosized particles (Abiodun‐Solanke et al. 2014). Various nanomaterials such as organic, inorganic, polymeric, and metallic nanostructures like dendrimers, micelles, solid lipid nanoparticles (SLNs), carbon nanotubes (CNTs), liposomes, niosomes, etc. have been successfully exploited in nanomedicine. Therefore, the use of these nanomaterials in the development of various nanodiagnostic tools (such as microchips, biosensors, nano‐robots, nano identification of single‐celled structures, and microelectromechanical systems) and therapeutic treatment approaches via target‐specific drug delivery has attracted a great deal of attention from the scientific community around the world (Liang et al. 2014; Núñez et al. 2018; Mitragotri and Stayton 2019).

      Currently, various diagnostic and therapeutic strategies are in practice which are very complex, time‐consuming, and also very costly. However, the recent advances in nanotechnology allow us to provide accurate, sensitive, rapid, and inexpensive diagnostic techniques, as well as treatments for the patients with the least number of possible interventions and without any adverse effects (Leary 2010; Gholami‐Shabani et al. 2018).

      Usually, drugs function through the whole body before they reach the specific disease‐affected zone. In this context, nanotechnology has opened up novel opportunities to deliver specific drugs using various nanomaterials as delivery vehicles. Such nanotechnology‐based drug delivery has the ability to achieve effective, precise, and target‐specific drug delivery in order to reduce the chances of possible side effects (Gholami‐Shabani et al. 2017). Suitable drug‐delivery techniques have two fundamentals: the capability to target and to control the drug release. Targeting will ensure high performance of the drug and decrease the side effects, particularly when acting with drugs that are recognized to kill cancer cells but can also kill healthy cells when delivered (Cho et al. 2008). The decrease or prevention of side effects can be effectively achieved by the controlled release of a drug. In this context, nanotechnology‐based drug delivery systems provide a healthier diffusion of the drugs inside the body as their size allows delivery through intra venous injection or other methods. The nano‐size of these particulate structures also reduces the exciter reactions at the injection spot. Initial attempts to direct cure in a specific set of cells involved conjugation of radioactive materials to antibodies specific to markers shown on the surface of cancer cells (Patra et al. 2018). ​

Although nanotechnology has shown a number of revolutionary promises in various fields, it is still at the juvenile stage and there are numerous fields to be explored. Therefore, it is believed that in the near future, nanotechnology will help us to understand various aspects of human physiology in a significant way and it will be boon for the betterment of the biomedical field. Considering the huge potential of nanotechnology in biomedicine, in the present chapter we have focused on the general concept of nanotechnology and nanomaterials commonly used as nanomedicine. Moreover, the role of various nanomaterials in diagnosis, drug delivery, and treatment of various diseases has also been presented. In addition, different challenges in the use of nanomaterials as nanomedicine are further discussed.

1.2 Nanomaterials Used in Diagnosis, Drug Delivery, and Treatment of Diseases

      From the many studies performed over the last couple of decades, it has been proven that nanotechnology has a huge impact on the development of therapeutics. To date, a variety of organic and inorganic nanomaterials have been developed to encapsulate and deliver therapeutic and imaging agents (Mitragotri and Stayton 2019). These nanomaterials have allowed encapsulation and targeted release of drugs. Some of the nanomaterials‐based drugs are already being used in patients, however many others are making excellent progress toward clinical translation. Some of the important organic and inorganic nanomaterials commonly used in diagnosis, drug delivery, and treatment of a wide range of diseases are briefly discussed here.

      1.2.1 Inorganic Nanomaterials

      Different inorganic nanomaterials discussed in the chapter have been successfully exploited directly or indirectly in the diagnosis and management of various diseases.

      1.2.1.1 Colloidal Metal Nanoparticles

Different colloidal metal nanoparticles (Figure 1.1a) have been reported as having potential applications in diagnosis, drug delivery, and treatment of many diseases. However, among the colloidal metal nanoparticles, colloidal gold nanoparticles (GNPs) are recognized as suitable nanocarriers for biomedicine, i.e. for the intracellular and in vivo delivery of genes, drugs, and as contrast agents because of their easy synthesis, large surface area, and flexible surface chemistry (Lewinski et al. 2008; Jeong et al. 2019). Moreover, these nanoparticles can be easily modified by conjugating smart polymers in order to develop novel drug delivery systems that have the ability to release their payload in response to outside stimuli (Yavuz et al. 2009; An et al. 2010). Furthermore, due to the above‐mentioned novel properties and their high molar absorption coefficient, GNPs can be directly or indirectly used for the diagnosis and management of various diseases including photothermal agents in cancer photothermal therapy (Liang et al. 2014). In addition, there are other metal nanoparticles like silver, copper, etc., that were potentially used as novel antimicrobial agents due to their promising antimicrobial properties.

Figure 1.1 Schematic illustration of various inorganic nanomaterials.

      1.2.1.2 Mesoporous Silica Nanoparticles

      Mesoporous silica nanoparticles (MSNPs) are another important group of inorganic nanomaterials (Figure 1.1b). These nanoparticles are also considered ideal candidates for biomedical applications due to their controllable morphologies, mesostructures with biocompatibility, and easy functionalization ability (Dykman and Khlebtsov 2012; Liu and Xu 2019). The presence of numerous silanol groups on the surface of MSNPs make them hydrophilic; moreover, their functionalization using a variety of groups helps to achieve

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