title: Citrate-stabilized gold nanoparticles as negative controls  for measurements of neurite outgrowth.
abstract: Gold nanoparticles (AuNPs) are promising candidates for medical diagnostics and therapeutics, due to their chemical stability, optical properties, and ease of functionalization. Citrate-stabilized reference materials also have potential as negative controls in toxicology studies of other nanoparticles. Here we examine the impact of 30 nm particles on the in vitro development of rat-cortex neural progenitor cells (NPCs), which mimic aspects of the developing neurological environment. AuNPs dispersed in a low serum culture medium initially agglomerated, but then remained stable during a three day incubation period, and agglomerated only slightly during a ten day incubation period, as determined by dynamic light scattering. Transmission electron microscopy indicated the presence of individual nanoparticles at all time points examined. Fixed cells were cross-sectioned by ion milling and imaged by scanning electronmicroscopy and helium-ion microscopy to evaluate particle incorporation. Individual nanoparticles could be resolved inside cross-sectioned cells. AuNPs were incubated with developing NPCs for ten days at concentrations of 0.5 μg/mL Au, 0.1 μg/mL Au, or 0.05 μg/mL Au. Adenosine triphosphate levels, as determined by bioluminescence measurements sensitive to low cell numbers, were not affected by AuNPs and the particles did not interfere with the assay. Multiple endpoints of neurite outgrowth were not altered by AuNPs, in particular, total neurite outgrowth per cell, a sensitive measure of neuronal development. Slide-level comparisons demonstrated the consistent response of NPCs to gold nanoparticles and a positive control chemical, neuroactive lithium. These results indicate that 30 nm citrate-stabilized AuNPs could serve as negative-control reference materials for in vitro measurements of neurite outgrowth.
authors.affiliation: Applied Chemicals and Materials Division, National Institute of Standards and Technology (NIST), Boulder, CO 80305, USA. kavita.jeerage@nist.gov
authors.forename: Kavita M
authors.initials: KM
authors.lastname: Jeerage
authors.forename: Tammy L
authors.initials: TL
authors.lastname: Oreskovic
authors.forename: Alexandra E
authors.initials: AE
authors.lastname: Curtin
authors.forename: Aric W
authors.initials: AW
authors.lastname: Sanders
authors.forename: Rani K
authors.initials: RK
authors.lastname: Schwindt
authors.forename: Ann N
authors.initials: AN
authors.lastname: Chiaramonti
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D019343:Citric Acid; D006046:Gold / Q000009:adverse effects; D053768:Metal Nanoparticles / Q000009:adverse effects; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D058953:Neural Stem Cells / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D016501:Neurites / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D051381:Rats
chemical_list: D019343:Citric Acid; D006046:Gold; D000255:Adenosine Triphosphate