## 1 Introduction  
Cancer is the second leading cause of death worldwide. This disease corresponds to a rapid and uncontrolled abnormal cell growth and can affect any part of the body. Today there are around 100 different types of cancer and an increase of around 70% of cancer types is expected in the next two decades [1; 2; 3]. Today cancer therapy strategies lack specificity, thus the development of safer and more efficient systems for chemotherapeutics delivery and/or new treatment methodologies is of great importance. Nanomedicine is an emerging and promising field in the discovery and development of new strategies for cancer treatment. The design and development of novel tailor-made nanosystems allow for accurate strategies to eliminate cancer cells by selective accumulation of systematically administered chemotherapeutics. The leaky vasculature and poor lymphatic drainage of the tumor tissues actually enhance the permeability and retention effects (EPR) [4; 5; 6; 7]. In the last decades, extensive research has been accomplished to make the transport of the chemotherapeutic agents even more precise, minimizing the collateral harmful effects on healthy tissues [8; 9; 10]. Other new approaches for cancer treatment have appeared with the emergence of stimuli-responsive nanomedicine such as photodynamic (PDT) and sonodynamic (SDT) therapies. In both cases, solid-state nanoparticles are used as the photo- or sonsensitizer, respectively. Both therapies are based on reactive oxygen species (ROS) generation and their ability to kill cancer cells. The ROS are originated by the partial reduction of the molecular oxygen (O\({}_{2}\)) into new species, being the hydroxyl radical (\({}^{\bullet}\)OH) the strongest radical ever described [11]. Oxygen is fundamental for the normal metabolic activity of all aerobic organisms, being vital for the correct maintenance of life. However, cellular survival implies the existence of a very strict redox homeostasis equilibrium and any instability may result in different types of diseases [12]. Namely, the excessive production of ROS provokes a disequilibrium in the redox state which may lead to cellular components (proteins, DNA, or lipids) damage. However, these effects, generated by the cellular oxidative stress, are being exploited for the development of new therapeutics for cancer treatment [13; 14], for example the PDT and SDT therapies [11]. As stated above, the principle behind the PDT and SDT is the generation of ROS using an external stimulus as ultraviolet (UV) or near-infrared (NIR) light, or low intensity ultrasounds (US), respectively [11]. PDT is based on the ability of a specific molecule or material, i.e., the photosensitizer, to be excited by the absorption of light at specific wavelengths and to generate free radicals. The interaction of the photoexcited sensitizer with molecular oxygen results in the production of ROS such as singlet oxygen, hydroxyl radicals, and superoxide ions. Several classes of materials have been successfully investigated as photosensizers for PDT including semiconducting nanoparticles [15], porphyrins, and other organic dyes [16]. PDT is however limited to superficial tumors treatment due to the light poor tissue penetration. Generally, the efficient penetration depth for PDT is reported to be up to 1 cm when NIR light sources are used. Although even larger penetration depths for PDT can be obtained with the help of optical fibers [17], this approach is limited to endoscopically reachable tumors. Moreover, PDT relies on the use of light-sensitive therapeutic agents, which prevents patients from sunlight exposure after administering of photosensitizer. SDT mainly relies on the activation of acoustic cavitation phenomena due to the interaction of the medium with US waves. Ultrasound consists of mechanical pressure waves able to induce the formation and the oscillations of gas microbubbles in the stimulated medium.