# Hybrid Quantum Dot as Promising Tools for Theranostic Application in Cancer
## 1 Introduction
By adjusting the particle size and size distribution of the QDs, a wide absorbance range with highly symmetric and narrow emission spectra can be achieved [32]. The different types of QDs are prepared by the bottom-up approach, which involves the assembling of their precursor in the molecular state into nanocrystals [33]. The promising techniques for the preparation of QDs are categorized into four basic approaches, which include biotemplate-based synthesis, colloidal synthesis, biogenic synthesis, and electrochemical assembly [27; 33]. These methods for the preparation of QDs are illustrated in Figure 1.  
Carbon nanomaterials (specifically carbon nanotubes, carbon dots, graphene, and graphene derivatives) and other nanomaterials of organic and inorganic origin are popular for their extraordinary composition and excellent inherent properties for diverse applications such as fluorescent, fingerprinting, photocatalysis, electromagnetic shielding, and electric applications [3; 34]. These nanomaterials have also made a pragmatic intervention in the field of biomedical engineering, contributing to research in tissue engineering, drug delivery, biosensing, bioimaging, and cancer theranostic [35]. It is functionalized with QDs as a hybrid nanoparticulate system called hybrid QDs, which have very small dimensions and theranostic utility in cancer. These hybrid systems are utilized to deliver drugs of synthetic/natural/biological origin and act as an imaging agent simultaneously, which are likely to increase their accumulation, specifically in the cancerous or tumor tissue. Thus, these versatile nanoparticulate systems as hybrid QDs have very wide utility in cancer detection/imaging and site-specific delivery of different types of therapeutics to the cancerous tissues (Illustrated in Figure 2). Figure 1: Schematic illustration of commonly used preparation approaches for QDs: (**A**) Colloidal synthesis approach. (**B**) Biotemplate-based synthesis approach. (**C**) Electrochemical assembly approach. (**D**) Biogenic synthesis approach. Reproduced from [PERSON] et al. [27], Dove Medical Press, 2022. The low drug efficacy in cancer may increase by improving the EPR (enhanced permeability and retention) effect and overcoming the tumor heterogeneity challenges through designing targeted hybrid QDs of a stealth nature [36]. RBC-camouflaged, light-responsive, carbon-based porous particles may be helpful in targeting and penetrating tumor tissues. Protein- and RBC membrane-targeted nanospromeges improve targeting and circulation half-life. Porous carbon/silica and graphene QDs as hybrid systems are photoresponsive and tumor-penetrating drug carrier systems for theranostic application [37]. Cyclodext (CDs) are natural, water-soluble cyclic oligosaccharides with hydrophilic exteriors and hydrophobic interiors that are known for their utility in drug delivery applications. Their primary and secondary hydroxyl groups on the outside are easy to modify, and their lipophilic inner cavities can be filled with lipophilic moiety by the formation of an inclusion complex. These types of carriers are utilized to improve the aqueous solubility of water-insoluble therapeutics/imaging agents and serve as a promising carrier or drug delivery system in cancer management through hybridization with QDs for theranostic application due to the presence of numerous hydroxyl groups on their surface [38]. The present manuscript provides a detailed discussion and recent advancements in QDs for their utilization to improve the efficacy of loaded therapeutics and imaging applications in the effective management of cancer. It provided a discussion on hybrid quantum dots as a cancer theranostics and emphasized the recent research development (mainly in the last 5 years) in the area of cancer theranostics utilizing hybrid quantum dots. Figure 2: Illustration highlighting the utility of hybrid QDs as cancer theranostics for various applications.