Fig. 7. Schematic of experimental design. (A) Full experimental procedure involves AuNPs (red spheres) being added to the cell culture environment after (A.i) cells have sufficiently attached to the culture dish. (A.ii) Following uptake of the particles into the cell via endocytosis during the incubation pulse, extracellular particles were washed out. (A.iii) Fresh culture medium without AuNPs was added and the cells were left until incorporated particles were processed into lysosomes (depletion phase). (B.i) During the incubation phase, cells constantly internalize AuNPs, which accumulate inside endosomes (green vesicles) and lysosomes (blue vesicles), their acquired SERS map data serves as the sample group for analysis. (B.ii) Following the wash-out, vesicular AuNPs are processed along the endolysosomal pathway and are eventually found exclusively in lysosomes. SERS maps of cells with only lysosomal AuNPs serve as the reference group for the data analysis. Reprinted with permission from A. Huefner, W.-L. Kuan, K. H. Müller, J. N. Skepper, R. A. Barker and S. Mahajan, ACS Nano, 2015. Copyright 2015 ACS Nano.