Evaluate the potential toxicity of quantum dots on bacterial metabolism by microcalorimetry

Herein, we evaluated the toxic effects of mercaptoacetic acid (MAA)-CdSe quantum dots (QDs), MAA-CdSe/ZnS QDs and cysteamine (CA)-CdSe/ZnS QDs on the growth of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by microcalorimetry. Thermogenic curves of bacteria were recorded and bioeffects of QDs on bacteria were investigated. The results suggested that both MAA-CdSe QDs and MAA-CdSe/ZnS QDs inhibited the E. coli growth but stimulated the S. aureus growth with dose-dependent type. The inhibition or stimulation efficiency of QDs on E. coli or S. aureus growth all decreased dramatically after UV irradiation, which was due to the liberation of more toxic Cd2+. In addition, MAA-CdSe/ZnS QDs and CA-CdSe/ZnS QDs affected the growth of E. coli and S. aureus differently. MAA-CdSe/ZnS QDs could not affect the growth of bacteria, while CA-CdSe/ZnS QDs inhibited the bacterial growth dramatically, which resulted from the negative charge on the surface of these bacteria.

► Microcalorimeter was applied for the investigations of the toxic effects of QDs on bacteria.
► The results indicate that the toxicity of these QDs may come from the toxic Cd2+ released.
► The results indicate electrostatic interaction is the main force between bacteria and QDs.
► The toxicity of these QDs can be varied efficiently by modifying with different ligands.