1.2.1.2 Quantum Dots
Histological assessment of solid tumors includes imaging and biopsy, and in most cases, surgery is performed to remove the primary tumor and evaluate the surrounding lymph nodes. Visible, fluorescent, and radiolabeled small molecules have been used as contrast agents to improve detection during real‐time intraoperative imaging, but unfortunately, the current dyes lack the tissue specificity, stability, and signal penetration needed for optimal performance. Graphene quantum dots are used in cancer‐targeted drug delivery. It was recorded that the mean survival time of tumor‐bearing mice can be extended by 2.5 times when treated with Qdots [20]. Semiconductor quantum dots having superior optical properties are well‐established fluorescent imaging probes.
Compared to conventional small molecule dyes, their size, high stability, non‐photobleaching, and water solubility made them a unique fluorophore. At the same time, there have been major concerns regarding their potential nanotoxicity because high‐quality Qdots often contain heavy metal elements [21, 22]. Newly emerged theranostic drug delivery system using quantum dots helped in a better understanding of the drug delivery mechanism inside the cells. Nanoscale quantum dots, with unique optical properties, have been used for the development of theranostics. Surface‐modified quantum dots and their applications became widespread in bioimaging, immune histochemistry, tracking intracellular drug, and intracellular molecules target [23]. Chemotherapy or PTT is always inefficient due to their inherent limitations, but their combination for the treatment of cancers has attracted great interest during the past few years. A promising theranostic agent, black phosphorus quantum dots (BPQDs), due to its excellent photothermal property, extinction coefficient, and good biocompatibility and biodegradability, hold great potential for cancer treatment. However, the rapid degradation of BP with oxygen and moisture causes the innate instability that is the Achilles’ heel of BP, hindering its further applications in cancer theranostics. The BPQDs‐based drug delivery system exhibited pH‐ and photo‐responsive release properties, which could reduce the potential damage to normal cells. The in vitro cell viability study showed a synergistic effect in suppressing cancer cell proliferation [24, 25]. Studies show that nanoplatform of BPQDs camouflaged with a platelet membrane (PLTm) carrying hederagenin (HED) significantly enhances tumor targeting and promotes mitochondria‐mediated cell apoptosis and autophagy in tumor cells [26].
1.2.1.3 Carbon Nanotubes
CNTs are one of the unique one‐dimensional nanomaterials discovered by SumioIijima in 1991. CNTs can be functionalized via different methods to perform their specific functions and received more and more attention in biomedical fields. It is because of their unique structures and properties, including high aspect ratios, large surface areas, rich surface chemical functionalities, and size stability on the nanoscale range [27, 28]. Being attractive carriers and mediators for cancer therapy, they have also been applied as mediators for PTT and photodynamic therapy to directly destroy cancer cells without severely damaging normal tissue.
CNTs are becoming one of the strongest tools that are available for various other biomedical fields as well as for cancer therapy [29]. CNTs are used as nanocarrier transporters to transport anticancer drugs, genes, and proteins for chemotherapy that makes them effective in delivering biomolecules and drugs [30, 31]. They have the ability to enter cells, and this behavior is independent of cell type and functional group at their surface.
Research shows a variety of chemically functionalized CNTs have the ability of biocompatibility with the biological environment. The behavior of the material can be regulated making them a useful tool for all kinds of diagnosis and therapeutic as well as drug delivery applications [32, 33]. Besides CNTs, MnO₂ nanotubes, platinum nanoparticles, paclitaxel‐loaded riboflavin, and thiamine‐conjugated multiwalled CNTs showed promising potential in the treatment of cancer [34–37].
1.2.2 Drug Delivery
The current drug delivery system for cancer treatments may have shown positive results, but they definitely have negative consequences as well. These drugs are toxic, have poor tissue selectivity, and continuously using them may increase resistance against them [38]. The toxicity of a drug is always a concern because most drugs are not tissue specific, i.e. they have the same effect on normal and abnormal cells. The use of nanotechnology makes it possible to have a specifically targeted drug delivery system. From size manipulation to creating various delivery vehicles, nanotechnology can help specifically to target and assemble in tumor cells [39].
1.2.2.1 Metal‐Based Drug Delivery
There are several metal‐based nanodrugs that have shown great success in treatments; however, they are known to produce large quantities of toxic and other harmful substances [40]. A way to lower the negative consequences of nanometal drugs is to modify their properties. For example, the study of biodegradable iron stents and cobalt‐chromium stents in porcine coronary arteries of juvenile pigs showed to have the potential to reduce chronic inflammation and premature recoil. Another study shows that modifying biocompatible and monodispersed iron oxide superparamagnetic nanoparticles with the combination of folic acid (FA) and polyethylene glycol (PEG) increased the affinity of nanoparticle uptake by targeted cells [41].
For antitumor therapy, two‐dimensional molybdenum disulfide (MoS₂) nanosheets have proved to be a good photothermal agent. An extensive study has shown that soybean phospholipid encapsulated MoS₂ nanosheets have shown good photothermal conversion performance and photothermal stability. In addition, soybean phospholipids can be found in nature, so the cost of obtaining it from natural resources is always lower than synthetically developing it. The reason MoS₂ nanosheets do not necessarily carry a drug to cancerous cells; however, as a photothermal agent, they can absorb near‐infrared reflectance (NIR) light and convert it into heat, which then can be transported to tumor cells. This process will bring the temperature to the critical temperature of 42 °C and result in efficient cell death. This was tested on mice with breast tumor growth by intravenously and intratumorally injecting soybean phospholipid molybdenum disulfide (SP‐MoS₂) nanosheets. Both methods showed suppression of growth of the tumor [42].
Metallic nanodrugs can also be used as antiseptics or for antimicrobial purposes. For example, hydrophilic metallic silver nanoparticle (AgNP) nanocomposites composed of a polymer matrix of N‐vinylpyrrolidone (poly [VT‐co‐VP]) have various uses in medicine especially as an ingredient in burn medicine. The study shows these metallic nanocomposites exhibiting antimicrobial activities toward Gram‐negative and Gram‐positive bacteria. Additionally, silver has shown to have more antimicrobial effect on Gram‐negative bacteria due to better linkage between the silver nanocomposites and the hydrophilic channels present in the outer membrane of Gram‐negative bacteria. In addition to antimicrobial properties, silver nanocomposites have shown to not precipitate or shrink when stored in an aqueous environment for four months. This is due to the stability of functional groups in the nanocomposites. It is proposed that these silver nanocomposites can be used for the treatment of various infectious diseases and can be quite useful after surgeries in which the major problems can be caused by exposure to bacteria [43].
1.2.2.2 Biotechnology‐Based Drug Delivery
There are various developments in drug delivery systems based on combinations of biomacromolecules and nanoparticles. Since drug delivery is popular in cancer treatment, most of the developments have occurred in oncology. For the treatment of malignant melanoma, folate‐decorated cationic liposomes have been developed as nonviral vectors of hypoxia‐inducible factor 1‐α siRNA (HIF‐1α siRNA). Hypoxia‐inducible factor 1‐α is a transcription