Figure 4

Peak wavelengths for cell ROI spectra following NP exposure at various doses and durations. Cells were exposed to 12, 24, 48, or 96 μg/mL AuNPs for 2, 5, 10, or 24 h. Peak wavelength increased (spectra red-shifted) with increasing NP exposure time and dose. To note, at 2 h, only cells exposed to the 96 μg/mL dose of AuNPs exhibited sufficient NP signal so that a peak wavelength could be determined. At all lower exposure doses (12, 24, 48 μg/mL) at 2 h, the measured spectra was dominated by cell scattering so peak wavelengths could not be calculated and are not shown. Error bars represent the standard error of the mean. Spectra were measured from 63 to 125 cells in each condition, but only spectra with sufficient NP signal were included in the analysis (see ‘Methods’ section and Additional file 1 for details). **p < 0.01. Color of the horizontal line underneath the **symbol indicates the exposure dose for which the comparison is made.