Atomic force microscopy analysis of commercial sunscreens and TiO2 nanoparticle (NP) standard solution. (A) Phase image of COM 1. (B) Three-dimensional topographical image of the TiO2 NP standard solution for a scan size of 5 mm £ 5 mm (left). Decreasing the scan size (2 mm £ 2 mm) enables the morphological determination of TiO2 NPs (right). The circles highlight the primary particles.