Quantification of Gold Nanoparticle Cell Uptake Under Controlled Biological Conditions and Adequate Resolution

Abstract

Aim: We examined cellular uptake mechanisms of fluorescently labeled polymer-coated gold nanoparticles (NPs) under different biological conditions by two quantitative, microscopic approaches. Materials & methods: Uptake mechanisms were evaluated using endocytotic inhibitors that were tested for specificity and cytotoxicity. Cellular uptake of gold NPs was analyzed either by laser scanning microscopy or transmission electron microscopy, and quantified by means of stereology using cells from the same experiment. Results: Optimal inhibitor conditions were only achieved with chlorpromazine (clathrin-mediated endocytosis) and methyl-β-cyclodextrin (caveolin-mediated endocytosis). A significant methyl-β-cyclodextrin-mediated inhibition (63–69%) and chlorpromazine-mediated increase (43–98%) of intracellular NPs was demonstrated with both imaging techniques, suggesting a predominant uptake via caveolin-medicated endocytois. Transmission electron microscopy imaging revealed more than 95% of NPs localized in intracellular vesicles and approximately 150-times more NP events/cell were detected than by laser scanning microscopy. Conclusion: We emphasize the importance of studying NP–cell interactions under controlled experimental conditions and at adequate microscopic resolution in combination with stereology.

Keywords::

• electron microscopy
• endocytosis inhibition
• laser scanning microscopy
• nanoparticle uptake
• polymer-coated gold nanoparticle
• stereology

Financial & competing interests disclosure

This study was supported by grants of the German Research Foundation (DFG, SPP 1313), the Swiss National Science Foundation and the Helmholtz Association. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Acknowledgements

The authors would like to thank Andrea Stokes and Mohamed Ouanella for their excellent technical assistance and to Dr Jose Maria Montenegro Martos for helpful discussions.

Additional information

Funding

This study was supported by grants of the German Research Foundation (DFG, SPP 1313), the Swiss National Science Foundation and the Helmholtz Association. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.