Toxicity Evaluation of Boron- and Phosphorus-Doped Silicon Nanocrystals toward Shewanella oneidensis MR-1

Silicon nanocrystals, also known as silicon quantum dots, are regarded as green alternatives to traditional quantum dots composed of heavy metal elements. While it is well-known that the semiconductor properties of these materials can be tuned by doping with p/n-type dopants (i.e., boron and phosphorus), there is a lack of systematic understanding of their potential environmental impact if released into the ecosystem. Here, we demonstrate that introduction of dopants, especially phosphorus, cause doped silicon nanocrystals to produce reactive oxygen species, resulting in significant toxicity to a model microorganism, Shewanella oneidensis MR-1. In addition, the interaction between bacteria cells and silicon nanocrystals was investigated using dark field microscopy and bio-TEM. Interestingly, boron-doped silicon nanocrystals tended to attach to the cell surface while this phenomenon was not observed for undoped or phosphorus-doped silicon nanocrystals.