involved in the effective management of cancer treatment, one of which is early detection. In order to detect uncontrolled growth, pathologists use cancer biomarkers. According to the US Food and Drug Administration (FDA), biomarkers are “any measurable diagnostic indicator that is used to assess the risk or presence of disease” [9]. Every cell type in the body has unique molecular features and characteristics.
Cancer cells, or other cells in response to the presence of abnormal growth in the body, release biomolecules that are different from the biomolecules released from healthy cells. These biomolecules are defined as biomarkers and can be used to define the molecular definition of cancer [10]. Examples of biomarkers include genes; gene products; specific cells; enzymes; hormones present in blood, urine, tissues, and other bodily fluids; proteins or protein fragments; and DNA‐ or RNA‐based fragments [11, 12].
There are several existing methods of detection available including:
1 the Papanicolaou test to detect cervical cancer and mammography for breast cancer detection for women,
2 prostate‐specific antigen (PSA) test for a blood sample of men to detect prostate cancer,
3 occult blood test for colon cancer detection, and
4 endoscopy, X‐rays, ultrasound imaging, CT scans, and MRI are used for various detection purposes.
However, there are many limitations to the current methods. Furthermost, these methods are not always successful at detecting cancer at early stages. In addition, they are neither affordable nor available to many people who require them. The priority should be to discover new methods of detections that are accessible when needed. For detection, nanomaterials’ physical, optical, and electrical properties are quite useful. Over the years, the development of nanomaterials such as quantum dots, gold nanoparticles (GNPs), carbon nanotubes (CNTs), magnetic nanoparticles, gold nanowires, and many others works to lessen the limits of the standard methods of detection and increase the precision of detection [12].
1.2.1.1 Gold Nanoparticles
In comparison with other nanomaterials, the nanostructure of metallic nanoparticles is most flexible due to the synthetic control of their shape, size, structure, composition, assembly, and encapsulation, along with the tenability of their optical properties. Within these metals, GNPs are extremely useful in biomedical applications because their preparation time is shorter and the process is simpler than the others. Gold nanospheres can be prepared by reducing auric acid with different concentrations of sodium citrate for size variation. In addition, the citrate capping on the gold particles can be replaced with biomolecules such as DNA, peptides, and antibodies; they form covalent and noncovalent bonds with GNPs [13].
There are many applications of GNPs in cancer imaging and cancer therapy. The combination of GNPs and dynamic light scattering, a technique usually used for nanoparticle size analysis, enabled the analysis and detection of chemical and biological target analytes such as proteins, DNA, viruses, carbohydrates, and chemical and environmental toxins [14, 15].
With regard to treatment, photothermal therapy (PTT) using GNPs can initiate a hyperthermic physiological response in the tumor [16, 17]. The GNPs are able to convert light into heat, which can “melt” the targeted tumor. Gold, in particular, is useful in PTT because of its specificity. They can be administered to a local tumor area, which decreases the chances of its distribution to healthy cells, a problem with the conventional cancer treatment methods [18]. They can also be used to prevent migration of tumors to other areas of the body. In 2017, a study showed that GNPs targeting the nuclear membrane of cancer cells can increase nuclear stiffness and prevent cell migration and invasion. The nanoparticles trapped at the nuclear membranes can lead to overexpression of lamin A/C protein that leads to cell stiffness [19].
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
