# Hybrid Quantum Dot as Promising Tools for Theranostic Application in Cancer
## 2 Significance of Hybrid Quantum Dot as Cancer Theranostics
### Perspectives of QDs for Diagnostic/Imaging Utility  
QDs in drug delivery may be utilized as therapeutic/imaging cargo that has photothermal and photodynamic features, making them excellent for bioimaging. Many clinically used photosensizers (PSs) are not tumor-targeted; hence, they are treated with spatially controlled irradiation. After phototherapies, PS can increase reactive oxygen species (ROS) formation in healthy cells; hence, light exposure should be avoided to reduce skin photosensitivity. The hybrid QDs possess low toxicity and good biocompatibility, coupled with stable photoluminescence (PL), and therefore these are ideal candidates for both in vitro and in vivo bioimaging [40; 41]. QDs by themselves are not as efficient as molecular PSs, but QDs can be used as antennae to improve light harvesting and energy transfer to molecular PSs because they absorb much light. NPs are commonly utilized for bioimaging, but their toxicity limits their utility. Because fluorescence imaging is very sensitive and has a good temporal and spatial resolution, hybrid QDs are a good choice for sensing and imaging cell targets. Hybrid QDs are chemically inert, dissolve well in water, are photostable, have a relationship between their optoelectronic properties and their shape and size, have fluorescence resonance energy transfer, high stability in physiological conditions, specific accumulation at target sites, are easy to modify on the surface [50], and have a high absorption coefficient because of hybridized C-C bonds. Therefore, these are good phototherapy chromophores. Carbon QDs (C-QDs) synthesized and dispersed with excellent fluorescence, photostability, photobleaching resistance, and simple coupling with biological species [51]. C-QDs can carry Ce\({}_{6}\) and generate ROS. Using a 639 nm laser, water splitting produced oxygen and hydrogen in vivo. Increased oxygen yielded \({}^{1}\)O\({}_{2}\) to improve PDT. C-QDs with specificcell targets can particularly detect malignant cells in different investigations. C-QDs conjugated with folic acid (FA) (C-dots-FA) to distinguish folate receptor (FR)-positive cancer cells from normal cells (FR-negative) by growing and analyzing NIH-3T3 and HeLa cells. Pheophytin (a natural, low-toxicity Mg-free chlorophyll derivative) was employed as a raw carbon source to synthesize C-QDs using a microwave technique [52]. QDs containing sulfur and nitrogen are used as PTT (photothermal therapy causes ease of cell death by protein denaturation and loosening of the cellular membrane by heating the tumor tissue exploiting irradiation of radiofrequency, ultrasound, microwaves, and magnetic fields, etc.) and PDT (photodynamic therapy utilizes a photosensitizer that absorbs light of a particular wavelength and produces oxygen-based molecular species to induce a cytotoxic effect) for cancers in animals [53; 54]. PL and photoacoustic imaging [55; 56; 57; 58] benefited from high photon conversion efficiencies. Passive targeting of QDs around cancer cells destroyed the tumor. Co-doped C-QDs had a strong photothermal conversion, optical and photoacoustic performance, and renal excretion [53; 59]. N-O-CQDs with significant NIR absorption. Combining the biocompatible N-doped carbon dots (N-CDs) with folic acid, which possess a wide range of high-targeting capabilities (26 types of tumor cell lines) and alters the cellular metabolism leading to autophagy, results in a new targeted tumor therapy based on autophagy regulation [60]. Similarly, maleimide-terminated TTA1 aptamers complexed with CDs (TTA1-CDs), which is substantially expressed in HeLa and C6 (rat glioma cell line) but not in normal healthy CHO cells, exhibit a strong fluorescence along cancer cell membranes and minimal uptake in healthy cells [61]. Graphene quantum dots (GQDs) are one type of nanocarrier that has been seen in physics and chemical research due to their ultrasmall size, varied photoluminescence, and mechanical features [62].