**1. Introduction**

Nanotechnology has opened a new avenue to investigate and explore the potentials of materials at the nanoscale with known functionality at the macroscale. The biomedical applications of nanoscale materials are supported by the evidence that most of the cellular organelles, cell membranes, protein ligands, and DNA sizes are ranged from 2 to 20 nm [1]. The interaction of materials with cellular organelles at the nanoscale can significantly enhance their desired biomedical application with enormous traceability. Nanotechnology is applicable in various areas of the healthcare system due to the distinguished biological and physicochemical properties of nanomaterials. Various nanostructures with distinct characteristics have been utilized in drug delivery, diagnostic probes, prosthetic implants, and biotechnological applications. Out of many, titanium dioxide (TiO2) has been extensively utilized [2].

TiO2 are metallic oxide nanoparticles, widely used, and are of great interest in modern therapeutics. They are semiconductive, highly stable, and possess anticorrosive and antibacterial characteristics. Titanium is the second most abundantly consumed metal, with daily 1–2 mg/kg consumption for children and 0.2–0.7 mg/kg for adults in the USA [3]. It is well distributed on the earth's crust and abundantly found in T, TiCl4, and TiO2. The anatase is the most reactive crystalline form of TiO2 compared to brookite, rutile, and TiO2-B1 as various polymorphs [4]. Titanium is well recognized for its exceptional characteristics, such as low weight, good mechanical strength, high wear resistance, and biocompatibility [5, 6]. They are less toxic than other nanomaterials and relatively economical to fabricate [7, 8]. Anatase and rutile exist in a tetragonal structure, whereas brookite is rhombohedral [9]. Moreover, an amorphous form of TiO2 can also be found [10].

Their white appearance is attributed to their high refractive index and is used in skin care products as a white pigment. They possess catalytic activity upon exposure to UV light and can be utilized for water treatment to remove the chemicals from them [8]. In addition, TiO2 has also been used as an additive in food products [11–14]. TiO2 is one of the most produced nanoparticles due to its wide range of applications [15]. TiO2 has been employed in biomedical applications such as molecular imaging, drug delivery system, and therapeutic approaches alongside conventional therapies or substitutes [16, 17]. Akira Fujishima was the first to discover its anticancer effect against human cervical cancer cells (HeLa). Photoactivation with UV light could generate hydroxyl (OH. ), per hydroxyl (H2O. ), and singlet oxygen (1 O2) as Reactive Oxygen Species (ROS) [18]. These ROS then interfere with cellular signal pathways and induce apoptosis by damaging the mitochondria. Different biomedical applications of nano titania are shown in **Figure 1**. This chapter focuses on combining various applications of titanium NPs in biomedicine, especially in various cancer

therapeutics and diagnostic purposes. We will also spotlight its applications in the specialized modalities viz. photodynamic and sonodynamic therapy as photosensitizers. In targeted cancer therapies, the use of nano titania as a delivery vehicle is highly favorable and this will be the main focus of this chapter.
