Figure 1

Illustrations of the detection of silica NM-201 based on electron density and of the primary particles of NM-201 and NM-203. The NM in the representative electron micrograph ( A) are detected, classified by mean diameter and false colour-coded in the corresponding annotated image ( B). Red: < 50 nm, green: 50–70 nm, blue: 70–100 nm, yellow: 100–200 nm, cyan: 200–300, pink: 300–500 nm and brown: > 500 nm. Particles at the borders of detection region are black and are omitted from analysis. Bar 500 nm. The selected electron micrographs illustrate the differences in primary particle size between NM-203 ( C) and NM-201 ( D). Bar 50 nm.