Quantum dots as theranostic nano delivery system in combating various diseases

Conventional chemotherapy lacks insolubility, selective targeting and bio-imaging of the chemotherapeutics aggravating the diseased state with developed drug resistant toxicity in the biological system. To overcome these obstacles and other biological barriers, nano-sized semiconductor quantum dots (QDs) having the unique photoluminescence and electronic physicochemical properties such as size-tunable light emission, narrow emission range, high brightness and photo-stability for making them the suitable diagnostic probe materials in bio/immune -sensing platform have attracted attention for targeted theranostic photodynamic therapy to bridge nanotechnology and cargo therapy assay. In general, QDs, linked to photoluminescence, induce generation of free radicals, disrupt cell walls/membranes and arrest gene expression as antimicrobial/anti-cancer agents in nano theranostic platform for concomitant sensing, imaging and therapy in the biological system. QDs may be conjugated with polymers, ligands, cargos and other biomolecules through covalent and non-covalent bonds for different specific targeting and controlled liberation of cargos to the diseased site/s of concern to get higher theranostic efficacy. This review focuses mainly the physicochemical characteristics of QDs, their synthesized methods, surface functionalizations, mechanism of action, biomedical applications, toxicity, biodistribution, pharmacokinetics and elimination as nano delivery system. Keywords: Conventional chemotherapy; Diseases; Quantum dots; Theranostic efficacy; Nano delivery system.