Figure 3

Co-registered image and analysis of 1.9 nm AuroVist gold nanoparticles in MDA-MB-231 cells.

(A) Cells incubated with 500 μg/ml gold particles for 24 hours before being fixed and stained with DAPI. Image contains both the surface plasmon resonance signal from two-photon interaction with gold particles (orange) and nuclei regions (blue). The GNPs are observed in the cytoplasmic regions with some of the gold particles accumulating close to the nuclear boundary regions. (B) Nuclei boundaries produced in image analysis by a varying binary threshold. The automatic threshold determined by ImageJ (white) in comparison to a lower threshold (green) and higher threshold (red). (C) Integrated gold signal of 20 cells for increasing distance from the nuclear membrane for the three thresholds chosen in (B). The automatic threshold outline (black line) produces a maximum gold intensity at 0.5 μm outside the nuclear membrane. The gold intensity reduces significantly across the membrane (distance = 0) and the gold signal within the nucleus (distances < 0) is consistent with the assumption that all of the gold is outside the nucleus, instead reflecting the measured point spread function (PSF) for the gold image of 0.5 μm. The integration was done taking account of the number of pixels in the image at each distance from the nuclear membrane. Hence to a good approximation the intensity is equivalent to the relative density of gold nanoparticles.