title: High-pressure freezing/freeze substitution and transmission electron microscopy for characterization of metal oxide nanoparticles within sunscreens.
abstract: OBJECTIVE
  To date, the description of a single, suitable method to observe in detail metal oxide nanoparticles in situ within sunscreens is currently lacking, despite growing concern as to how they interact with humans. This study explores the usefulness of transmission electron microscopy to characterize the nanoparticles in sunscreens.
  
  
  METHODS
  High-pressure freezing then freeze substitution was used to prepare resin-embedded commercial sunscreen samples, and ultrathin sections of these were observed with transmission electron microscopy. Conventional room temperature processing for resin embedding was also trialed.
  
  
  RESULTS
  High-pressure frozen/freeze substituted samples provided clear visualization of the size and shape of the nanoparticles and agglomerates and allowed further characterization of the composition and crystal form of the metal oxides, while conventionally processed chemically fixed samples were subject to distribution/agglomeration artifacts.
  
  
  CONCLUSIONS
  Transmission electron microscopy of high-pressure frozen/freeze substituted samples is an ideal method to completely observe metal oxide nanoparticles in situ in sunscreens.
authors.affiliation: Australian Microscopy & Microanalysis Research Facility & Australian Institute for Bioengineering & Nanotechnology, Cnr College & Cooper Roads, The University of Queensland, Brisbane, Queensland, 4072, Australia. m.butler1@uq.edu.au
authors.forename: Margaret K
authors.initials: MK
authors.lastname: Butler
authors.forename: Tarl W
authors.initials: TW
authors.lastname: Prow
authors.forename: Ya-Nan
authors.initials: YN
authors.lastname: Guo
authors.forename: Lynlee L
authors.initials: LL
authors.lastname: Lin
authors.forename: Richard I
authors.initials: RI
authors.lastname: Webb
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Martin
mesh_terms: D017110:Freeze Substitution / Q000379:methods*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D046529:Microscopy, Electron, Transmission / Q000379:methods*; D010087:Oxides / Q000737:chemistry*; D013473:Sunscreening Agents / Q000737:chemistry*
chemical_list: D010087:Oxides; D013473:Sunscreening Agents