This is a top-down approach that uses a high-energy laser beam to vaporize a carbon target. This method enables precise control over the size and surface chemistry of CQDs [18]. In this technique, a carbon target is irradiated with a high-energy laser beam in the presence of a suitable solvent. The intense laser energy causes the carbon target to vaporize, generating CQDs that are subsequently dispersed in the solvent. This method enables precise control over the size and surface chemistry of CQDs [19].

Feng et al. [35], employed the photoluminescence feature of CQDs as a detectable nanocarrier modified by polyethylene glycol, RGD, and Pt (IV) for delivering cisplatin in a targeted manner. They obtained a pH-sensitive drug release behavior in the tumor microenvironment. Moreover, their results revealed that cisplatin (IV) has turned into cisplatin (II) after cellular uptake during the reduction process within the cytoplasm, indicating an effective targeted anticancer activity. In another study, Gong et al. [36], employed phosphorus and nitrogen-doped CQDs to carry doxorubicin (DOX) and to release drug in a pH-sensitive environment. Their release outcomes

demonstrated an enhanced drug release and fast DOX uptake by the cancer cells. Furthermore, Shu et al. [37] employed organophilic CQDs as a nanocarrier for curcumin (CUR) with a high loading capacity. They showed that chemotherapy effi­cacy was enhanced due to the increased permeability of CUR-loaded organophilic CQDs. Besides, Yang et al. [38] developed polyamine including organosilane struc­tures made CQDs less active to carry DOX as an active agent for targeted delivery and theragnostic applications to treat breast cancer cells (MCF-7). Their results indicated low cytotoxicity toward healthy tissues and improved MCF-7 apoptotic effects under exposure to DOX-loaded CQDs with above 62% loading capacity. Sung et al. [39] developed a photo-sensitive nanocarrier for encapsulating docetaxel into the sponge-like carbon dot structures modified by red blood cells as the outer membrane. Their results showed an enhanced apoptotic effect against targeted tumors under the NIR irradiation and during the 3-week treatment process. In some studies, CQDs have been functionalized by folic acid (FA) as a ubiquitous ligand for targeted cancer therapy with a high affinity toward repeatedly expressed folate receptors on diverse tumor cells. In this regard, Li et al. [40], employed functionalized and N­doped CQDs with FA as the alternative chemotherapy procedures to treat cancers. They obtained the visualized cancer therapy through above 93% cellular uptake and within the 30-day survival period during phthalocyanine with FA as the targeting ligand for targeted cancer therapy. Their results showed an enhanced apoptotic effect against HeLa cell lines. Furthermore, Zhang et al. [41] fabricated the func­tionalized FeN@CQDs nanocomposites with riboflavin and FA for assisted photo­responsive delivery of DOX in a targeted manner synergistically with photothermal­thermodynamic combination therapy procedures to optimize the cancer treatment efficacy. Their results indicated an enhanced DOX delivery under the NIR irradi­ation as the external stimulus. In the provided Fig. 2a, the fabrication process of the polymeric-based nanomaterials composed of CDs have been depicted, which have been fabricated through diverse natural and synthetic procedures with required physicochemical modifications. Furthermore, the application of these materials is summarized in the Fig. 2b.

yield. Afterward, the nanoparticles are conjugated with biotin and loaded with 5-fluorouracil (5-FU) as an anti-cancer drug to act as a functional cell-targeted nano-theranostic tool. Comparing the localization of CQDs with biotin-CQDs, it is suggested that the biotin-CQDs are distributed in the whole cell, chiefly in the nucleus, highlighting suitable cell-targeting properties [54]. In another study, Gogoi et al. synthesized calcium alginate beads coated with chitosan-based CQDs. The synthesized biomaterial revealed appropriate stability over two months in atmo­spheric conditions. In this system, carboxylate residues of alginate and protonated amino residues of chitosan ironically interact with each other and form a polyelec­trolyte complex. Moreover, they employed Tetracycline, an antibiotic exhibiting anti­inflammatory action and effective against imbalance diseases, and β-cyclodextrin as a complexing agent for evaluation of drug release behavior of nanocarriers. The results show more than 90% drug loading and 61% drug release at pH 1 [55].