Cellular internalization and intracellular biotransformation of silver nanoparticles in Chlamydomonas reinhardtii

Abstract

It is necessary to elucidate cellular internalization and intracellular biotransformation in order to accurately assess the toxicity and fate of nanoparticles after interaction with organisms. Therefore, this work employed a combination of high resolution imaging and in situ detection spectroscopic techniques to systematically investigate the intracellular localization, morphology and chemical speciation of silver in the cells of Chlamydomonas reinhardtii, a unicellular freshwater green alga, after exposure to AgNPs coated with polyvinylpyrrolidone at a concentration of 2.0 mg/L. High resolution secondary ion mass spectrometry and high-angle annular dark field scanning transmission electron microscopy together with energy dispersive spectroscopy and selected area electron diffraction collectively confirmed that after 48 h of exposure, AgNPs entered the periplasmic space after cellular internalization into the algal cells. Silver was also found to coexist with sulfur inside the cytoplasm in both crystalline and amorphous forms, which were further identified as β-Ag₂S and silver thiolates with synchrotron X-ray absorption spectroscopy. In combination, these analyses demonstrated that silver inside algae could be attributed to the uptake and sequestration of Ag⁺ ion released from AgNPs, which was further sequestrated into cellular compartments. This study provides solid evidence for particle internalization and biotransformation of AgNPs after interaction with algae.

• Chlamydomonas reinhardtii
• HAADF-STEM
• NanoSIMS
• silver nanoparticles
• XAS

Acknowledgments

We are grateful to Dr. Jun Weng and Fei Shi for their advice on sample preparation for NanoSIMS analysis and François Horréard, François Hillion and Adina Lazar from CAMECA, France for their generous support in the NanoSIMS detection and data analysis. We thank the Shanghai Synchrotron Radiation facility for the provision of synchrotron beam time under award 13SRBL14W16825.

Declaration of interest

The authors report no conflicts of interest and are responsible for the content and writing of the paper. Financial supports were provided by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDB14020202) and the National Natural Science Foundation of China (Projects 21321004 and 21277154) .

Supplementary material available online

Supplementary Table S1 and Figures S1–S8