# Hybrid Quantum Dot as Promising Tools for Theranostic Application in Cancer
## 2 Significance of Hybrid Quantum Dot as Cancer Theranostics
### Perspectives of QDs for Therapeutic Utility  
Different QD-based therapeutic systems for anticancer application have been widely explored in recent years [73; 74]. Various studies have been conducted to investigate the potential of QDs for targeted drug delivery, PDT, PTT, and gene delivery in cancer treatment [75; 76]. The QDs for cancer therapy have been investigated both at in vitro and in vivo levels. PDT is one of the most promising non-invasive cancer treatment approaches with limited side effects. It can be used alone or in combination with surgery, chemotherapy, or ionizing radiation to destroy undetected cancerous cells at the margins of resection. PDT uses photosensitizing drugs that are pharmacologically inactive until a particular light wavelength irradiates them in the presence of oxygen, which generates reactive oxygen species and induces cell death and tissue necrosis [77; 78]. Graphene oxide (GO), an oxidized version of graphite, has received considerable attention during the past decade. GO, on the other hand, can be dispersed in water, which makes it a good candidate to investigate in a biological system. On the other hand, graphenes need to be surface functionalized to make them dispersible in water and safer for the biological environment [79; 80]. Their synthesis and surface tailoring entail hazardous and toxic reagents, traces of which may remain with the material to demonstrate further toxicity in vitro/in vivo systems due to GO sheets having intrinsic toxicity. By delivering medications and energy in two different locations at the same time, a hybrid system of nano dimension may be able to lessen the adverse effects of cancer treatment and improve the distinctive properties required for precision medicine. The hybrid carrier systems are frequently eliminated from blood circulation very quickly, and piled-up tumors at the periphery close to the blood arteries. It has a short elimination half-life in blood and high tumor penetration. The membrane of a red blood cell (RBC) was given the appearance of a sponge by being composed of carbon composite. When it is exposed to light, it functions as both a \"stealth agent\" and a \"photolytic carrier\". It means that it transfers \"tumor-penetrating agents\" (such as graphene QDs and docetaxel) as well as heat. When compared to the nanosponge, the RBC-membrane-enveloped nanospongedemonstrates an eight-fold increase in accumulation in tumor tissue. This is because the RBC-membrane-enveloped nanosponge will be integrated with a specific protein that accumulates in tumor spheroids through high lateral bilayer fluidity [81]. The delivery of graphene QDs to tumor areas is accomplished by passing near-infrared light through a structure that is only one atom thick. This makes it much simpler for its therapeutic utilization to penetrate the cancerous tissue and improves the prognosis of cancer therapy utilizing the theranostic approach.  
The pathway of accumulation and removal of QDs and hybrid QDs in in vivo systems are depicted in Figure 3.  
Different types of hybrid QD-based theranostic systems were explored for cancer applications to improve the biopharmaceutical attributes of this nanoparticulate system (such as aqueous solubility, tumor penetrability, and stability of loaded therapeutics in the tumor microenvironment) and delivery of drug specifically to tumor tissues. Recent contemporary research conducted in this field is discussed in the subsequent section.