title: Synthesis, characterization, and direct intracellular imaging of ultrasmall and uniform glutathione-coated gold nanoparticles.
abstract: Gold nanoparticles (AuNPs) with core sizes below 2 nm and compact ligand shells constitute versatile platforms for the development of novel reagents in nanomedicine. Due to their ultrasmall size, these AuNPs are especially attractive in applications requiring delivery to crowded intracellular spaces in the cytosol and nucleus. For eventual use in vivo, ultrasmall AuNPs should ideally be monodisperse, since small variations in size may affect how they interact with cells and how they behave in the body. Here we report the synthesis of ultrasmall, uniform 144-atom AuNPs protected by p-mercaptobenzoic acid followed by ligand exchange with glutathione (GSH). Quantitative scanning transmission electron microscopy (STEM) reveals that the resulting GSH-coated nanoparticles (Au(GSH)) have a uniform mass distribution with cores that contain 134 gold atoms on average. Particle size dispersity is analyzed by analytical ultracentrifugation, giving a narrow distribution of apparent hydrodynamic diameter of 4.0 ± 0.6 nm. To evaluate the nanoparticles' intracellular fate, the cell-penetrating peptide TAT is attached noncovalently to Au(GSH), which is confirmed by fluorescence quenching and isothermal titration calorimetry. HeLa cells are then incubated with both Au(GSH) and the Au(GSH)-TAT complex, and imaged without silver enhancement of the AuNPs in unstained thin sections by STEM. This imaging approach enables unbiased detection and quantification of individual ultrasmall nanoparticles and aggregates in the cytoplasm and nucleus of the cells.
authors.affiliation: Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA. sousaali@mail.nih.gov
authors.forename: Alioscka A
authors.initials: AA
authors.lastname: Sousa
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Morgan
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Brown
authors.forename: April
authors.initials: A
authors.lastname: Adams
authors.forename: M P Suresh
authors.initials: MP
authors.lastname: Jayasekara
authors.forename: Guofeng
authors.initials: G
authors.lastname: Zhang
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ackerson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kruhlak
authors.forename: Richard D
authors.initials: RD
authors.lastname: Leapman
mesh_terms: D005978:Glutathione / Q000737:chemistry* / Q000378:metabolism; D006046:Gold / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D053768:Metal Nanoparticles / Q000737:chemistry*; D017348:Microscopy, Electron, Scanning Transmission; D010316:Particle Size
chemical_list: D006046:Gold; D005978:Glutathione