In future, quantum dots could be used in medicine for cancer therapy. With the help of certain coatings, the nanoparticles should be able to selectively accumulate in the tumour tissue and at the same time prevent nonspecific deposition in organs such as the liver and spleen. For a safe medical application it is equally important to ensure the excretion of any kind of any drug or nanoparticle injected into the body after a reasonable amount of time [1,2].


The longer cadmium-based quantum dots reside in the body, the greater is the chance of coating degeneration, subsequent leakage of cadmium ions and thus the induction of toxicity at sides of deposition.

Therefore, scientists systematically analysed the renal excretion of cadmium-based quantum dots in various sizes and surface modifications in a rat model. With increasing particles size the renal clearance rate of the quantum dots was drastically reduced and the larger nanoparticles were found in the liver, lung, and spleen instead. Consequently, the hydrodynamic diameter of the quantum dots used in biomedical applications should not exceed 5.5 nanometres for rapid and efficient urinary excretion. Binding of serum proteins may also result in an increase in hydrodynamic diameter up to 15 nm, as they preferentially bind to positively or negatively charged quantum dots. This behaviour can be avoided by using a suitable coating [3].


In conclusion, the production of quantum dots suitable for in vivo applications is complex and requires consideration of various other aspects in addition to the desired functionalities. On the one hand, the quantum dots with their respective coating should be as stable as possible to prevent leakage of cadmium ions. But on the other hand, a quick an efficient clearance of the nanoparticles from the body can only be ensured for quantum dots smaller than 5 nanometres, which is virtually impossible with currently used coatings.




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