Commercialized CdSe/ZnS quantum dot nanoparticles are surprisingly not assimilated and most likely nontoxic to aquatic organisms like Daphnia magna, according to research led by the director of Dartmouth’s Trace Element Analysis Core Laboratory Brian Jackson. The discovery was published earlier this month in Analytical and Bioanalytical Chemistry.

“There was a huge public outcry and concern of the toxicity of nanoparticles, which are widely used in industries. So, there was a huge amount of funding poured into this. We thought this is important and that’s why we are doing this,” said Jackson in an interview with DUJS.

Quantum dots (QDs) are very small semiconductor particles, usually less than 10 nm. Due to their unique property of being intensely fluorescent, they present great utility in many markets from optical and electronic applications to medical applications like cellular imaging.

QDs’ small size suggests that they may be easily assimilated by exposed organisms and hence cause toxicity. In particular, CdSe QD has been shown to have cytotoxic effects. A key question concerning the potential toxicity of QDs is whether they can cross the gut after ingestion. By crossing this barrier, they could be absorbed in internal organs, imparting toxicity as individual ions.

The research team exposed Daphnia magna to “red” and “green” CdSe/ZnS. For the green dots, the CdSe core is around 3 nm and for the red dots, the CdSe core is 6 nm. The researchers used synchrotron X-ray fluorescence (SXRF) to study the distribution of zinc (Zn) and selenium (Se) in the organism over a period of 36 hours. SXRF is valuable for rapid, nondestructive trace element analysis of geological and biological specimens.

The researchers found that there was no evidence of assimilation of QDs across the gut of Daphnia for both red and green QDs, implying that particle size had no effect.

Further, previous researchers concluded that the surface coating on QDs used to impart water solubility is key in determining passage across the cell membrane, since QDs greater than 5 nm cannot pass through and be absorbed. Jackson’s team used QDs surface-coated by MUA to facilitate water solubility, a coat commonly used in industries. The monolayer of MUA is around 25 nm, which far surpasses the maximum size of 5nm if QD were to be assimilated. Hence, QDs coated with water soluble layer may be too big to cause toxicity in aquatic organisms.

“We are satisfied with the results. But there is still much to learn about these QDs and our research will continue. A clear understanding of QDs will hold great importance as they become mass produced in the future,” said Jackson.