High-pressure freezing/freeze substitution and transmission electron microscopy for characterization of metal oxide nanoparticles within sunscreens

• Published in: Nanomedicine (London, England) Vol. 7; no. 4; pp. 541 - 551
• Main Authors: Butler, Margaret K, Prow, Tarl W, Guo, Ya-Nan, Lin, Lynlee L, Webb, Richard I, Martin, Darren J
• Format: Journal Article
• Language: English
• Published: England Future Medicine Ltd 01.04.2012
• Subjects: characterization; Chemical properties; Freeze Substitution - methods; Health aspects; Metal Nanoparticles - chemistry; Metal Nanoparticles - ultrastructure; metal oxide nanoparticles; Microscopy, Electron, Transmission - methods; Nanoparticles; Oxides - chemistry; particle characterization; sunscreen; Sunscreening Agents - chemistry; Sunscreens (Cosmetics); Transmission electron microscopes; transmission electron microscopy; Australia
• ISSN: 1743-5889; 1748-6963; 1748-6963
• DOI: 10.2217/nnm.11.149

To date, the description of a single, suitable method to observe in detail metal oxide nanoparticles 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. 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. 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. Transmission electron microscopy of high-pressure frozen/freeze substituted samples is an ideal method to completely observe metal oxide nanoparticles in sunscreens.