PEG-PAA micelle—Poly(ethylene glycol)-polyacrylic acid, PEG-PLA micelle—Poly(ethylene glycol)-polylactide micelles, FDA—Food and Drug Administration.

### *3.4. Carbon Nanotubes (CNTs)*

CNTs are carbon-based cylindrical molecules that can be employed as nanocarriers in cancer therapy. CNTs are produced from graphene sheets rolled into a seamless cylinder with a high aspect ratio, diameters as small as 1 nm and their lengths can reach up to several micrometres and they can be open-ended or capped [63]. The two types of carbon nanotubes are single-walled carbon nanotube (SWCNTs) and multi-walled carbon nanotubes (MWCNTS). Single-walled carbon nanotubes are single graphene cylinders, whereas multi-walled carbon nanotubes are a complex nesting of graphene cylinders. SWCNTs have a smaller diameter, are more flexible and can help with imaging. On the other hand, MWCNT's have a large surface area and so the endohedral filling is more efficient [64–66]. Carbon nanotubes received more attention among other carbon-based nanocarriers and spherical nanoparticles due to their distinctive properties such as intracellular bioavailability, high cargo loading and ultra-high aspect ratio [67,68]. The schematic representation of multifunctional CNTs are shown in Figure 5.

CNTs have been utilized in a variety of applications, including anticancer drug delivery and gene therapy. Non-spherical nanocarriers like carbon nanotubes can stay in lymph nodes for longer than spherical nanocarriers like liposomes [63]. According to Yang et al., CNTs could be utilised to target lymph node tumours. In this study, FA-functionalized MWCNTs were used to entrap magnetic nanoparticles incorporated with cisplatin. The nanotubes were dragged to the lymph nodes using an external magnet and the drug release was achieved for several days in the tumour cells [69,70]. To make CNTs smart, they should be functionalized chemically or physically [71]. PEGylation is a critical step in increasing solubility, avoiding RES and reducing toxicity [72].

6 MWCNTs Doxorubicin folic acid, Polyethylene glycol HeLa cells # SWCNTs—Single walled carbon nanotubes, MWCNTs—Multi-walled carbon nanotubes.

Table 4. CNTs for cancer therapy. Reproduced with permission from reference [77].

4 MWCNTs # Doxorubicin Polyethyleneimine, hyaluronic

1 SWCNTs # Doxorubicin & mi-

3 SWCNTs Doxorubicin

5 MWCNT Docetaxel, couma-

2 SWCNTs

toxantrone

7-Ethyl-10-hydroxycamptothecin (SN38)

rin-6

S. N. Type Drug Functionalization Cancer Cells

Polyethylene glycol, fluores-

Polyethylene glycol, antibody C225, folic acid

Folic acid, Chitosan & its derivatives (palmitoyl chitosan & carboxymethyl chitosan)

D-Alpha-tocopheryl, polyethylene glycol 1000 succinate (TPGS), transferrin

cein, folic acid HeLa cells

acid, fluorescein isothiocyanate HeLa cells

Colorectal cancer cells

Human cervical cancer HeLa cells

Human lung cancer cells

Figure 5. Schematic representation of multifunctional carbon nanotubes. **Figure 5.** Schematic representation of multifunctional carbon nanotubes.

3.5. Gold Nanoparticles (AuNPs) AuNPs have received current scientific interest among numerous nanocarriers developed for use in nanomedicines due to their unique uses in cancer therapy such as drug delivery, tumour sensing and photothermal agents [78]. For a variety of reasons, the use of AuNPs in cancer treatment and diagnosis is gaining a lot of interest. Furthermore, their inactivity toward biological systems has made them superior to conventional metal-based drug delivery technologies [79]. The inorganic nanoparticles have non-sensitive physicalchemical properties and are meant to convert irradiation energy into harmful radicals for photodynamic or photothermal therapy for solid malignancies. Due to their unique features, inorganic nanoparticles serve an important role in a variety of domains, including drug processing, bioimaging and sensing. Inorganic nanocarriers such as gold nanoparticles perform an essential pharmacological role. When AuNPs are adjusted to a proper shape and size, they are likewise non-toxic and have low phototoxicity [80,81]. The sche-Another area of research that is now being investigated is the use of functionalized carbon nanotubes as a nanocarrier for gene therapy. Biomolecules such as miRNA, siRNA, dsDNA and others, in comparison to small molecule drugs, cannot enter cellular membranes and are quickly breakdown by nucleases [68,73]. On the surfaces of carbon nanotubes both RNA and DNA can easily accommodate, improve the therapeutic efficacy of aptamers, micro-RNA (miRNAs) and small interference RNA (siRNAs), oligonucleotides and double-stranded DNA (dsDNA) and because of their extraordinary flexibility and structure, carbon nanotubes can also carry large amounts of genetic materials to targeted areas [74,75]. The different types of CNTs used for cancer therapy are shown in Table 4. In the treatment of cancer, immunotherapy may be an alternative to gene therapy. SWNTs were coated with tumour-specific fluorescent probe, radiometal ion chelates and monoclonal antibodies. A variety of approaches have been shown to be capable of targeting the tumour (lymphoma) [76].


matic representation of multifunctional gold nanoparticles are shown in Figure 6. **Table 4.** CNTs for cancer therapy. Reproduced with permission from reference [77].
