There have been rapid increases in consumer products containing nanomaterials, raising concerns over the impact of nanoparticles (NPs) to humankind and the environment, but little information has been published about mineral filters in commercial sunscreens. It is urgent to develop methods to characterize the nanomaterials in products. Titanium dioxide (TiO) and zinc oxide (ZnO) NPs in unmodified commercial sunscreens were characterized by laser scanning confocal microscopy, atomic force microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that laser scanning confocal microscopy evaluated primary particle aggregates and dispersions but could not size NPs because of the diffraction limited resolution of optical microscopy (200 nm). Atomic force microscopy measurements required a pretreatment of the sunscreens or further calibration in phase analysis, but could not provide their elemental composition of commercial sunscreens. While XRD gave particle size and crystal information without a pretreatment of sunscreen, TEM analysis required dilution and dispersion of the commercial sunscreens before imaging. When coupled with energy-dispersive X-ray spectroscopy, TEM afforded particle size information and compositional analysis. XRD characterization of six commercial sunscreens labeled as nanoparticles revealed that three samples contained TiO NPs, among which two listed ZnO and TiO, and displayed average particle sizes of 15 nm, 21 nm, and 78 nm. However, no nanosized ZnO particles were found in any of the samples by XRD. In general, TEM can resolve nanomaterials that exhibit one or more dimensions between 1 nm and 100 nm, allowing the identification of ZnO and TiO NPs in all six sunscreens and ZnO/TiO mixtures in two of the samples. Overall, the combination of XRD and TEM was suitable for analyzing ZnO and TiO NPs in commercial sunscreens.

Numerous consumer products, such as cosmetics, contain nanoparticles (NPs) of titanium dioxide (TiO) or zinc oxide (ZnO); however, this raises questions concerning the safety of such additives. Most of these products do not indicate whether the product includes NPs. In this study, we characterized metal oxide NPs according to size, shape, and composition as well as their aggregation/agglomeration characteristics. In order to comprehend quickly the characterization of metal oxide NPs, we employed single particle inductively coupled plasma (SP-ICPMS) to help quantify the size of metal oxide NPs; then, we use transmission electron microscopy (TEM) to corroborate the results. The crystal size and structure was measured by X-ray diffraction (XRD), there are two crystal phase of TiO NPs in sunscreen powder showed in XRD. However, SP-ICPMS proved highly effective in determining the size of NPs, the results of which remarkably good agreement with the TEM measurements. Pre-treatment included a conventional copper grid (requiring sample dilution) to evaluate the size, shape and composition of primary particles or plastic embedding (without the need for sample dilution) to evaluate the aggregate/aggregation of native NOAAs. The proposed method is an effective and fast approach to the characterization of oxide NPs in cosmetic sunscreen powder. These findings outline an alternative approach to the analysis of NPs in powder-form matrix.

This study discusses the strategies on sample preparation to acquire images with sufficient quality for size characterization by scanning electron microscope (SEM) using two commercial ZnO nanoparticles of different surface properties as a demonstration. The central idea is that micrometer sized aggregates of ZnO in powdered forms need to firstly be broken down to nanosized particles through an appropriate process to generate nanoparticle dispersion before being deposited on a flat surface for SEM observation. Analytical tools such as contact angle, dynamic light scattering and zeta potential have been utilized to optimize the procedure for sample preparation and to check the quality of the results. Meanwhile, measurements of zeta potential values on flat surfaces also provide critical information and save lots of time and efforts in selection of suitable substrate for particles of different properties to be attracted and kept on the surface without further aggregation. This simple, low-cost methodology can be generally applied on size characterization of commercial ZnO nanoparticles with limited information from vendors.