3.2. LSCM analysis
LSCM is a nondestructive method utilized to estimate particle
size and distribution in sunscreens but cannot determine
exact NP sizes [12]. LSCM images of untreated commercial
sunscreens COM 1e6 were compared with those of the ZnO NP
standard solution (Fig. 3). Sunscreen samples exhibited larger
particles than the control solution. In addition, COM 1, COM 2,
and COM 5 presented a more even particle dispersion
compared with COM 6. LSCM images showed differences in
optical contrast between organic residues and inorganic particles
present in the sunscreens. LSCM provided insight on the
aggregation and dispersion of primary particles but did not
differentiate individual NPs because of the limited resolution
of optical microscopy (200 nm). In addition, the low contrast of
the sunscreen components may limit their resolution because
the image contrast was based on different refractive indices
[12]. Therefore, LSCM is not appropriate for particle size
determination in cosmetic products.