QUANTUM DOTS: AN EMERGING PLATFORM FOR DIAGNOSIS AND TARGETED THERAPY

Abstract Quantum dots (QDs) are semiconductor nanocrystals whose size-tunable fluorescence, high brightness and resistance to photobleaching make them attractive probes and carriers for cancer diagnosis and therapy. Surface functionalisation with antibodies, peptides, aptamers and folate allows QDs to recognise tumour-associated markers, supporting sensitive multiplexed imaging, sentinel lymph node mapping and image-guided drug delivery. However, the heavy-metal content of conventional cadmium-based QDs raises concerns about toxicity, persistence and biodistribution. Graphene quantum dots (GQDs), carbon-based nanostructures smaller than about 10 nm, have therefore emerged as a promising alternative, offering excitation-dependent photoluminescence, good photostability, low cytotoxicity and a large, readily modified surface. This review summarises the properties of QDs and GQDs, top-down and bottom-up synthesis routes, QD-based strategies for cancer detection, and the use of GQDs as nanocarriers, stimulus-responsive delivery systems and photosensitising nanocomposites for photodynamic therapy. The role of nanocarriers in overcoming drug resistance associated with cancer stem cells is also discussed. Finally, the main challenges, namely long-term biocompatibility, clearance, reproducible large-scale synthesis, targeting specificity and regulatory requirements, are outlined together with future prospects for QD- and GQD-based theranostic platforms in precision oncology. Keywords: Quantum dots; Graphene; Cancer imaging; Drug delivery; Theranostics; Toxicity