Fig. 4.

Observation of single FNDs in a HeLa cell. (A) Bright-field and epifluorescence images of a HeLa cell after uptake of 35-nm FNDs. Most of the uptaken FNDs are seen to distribute in the cytoplasm. (B) Epifluorescence fluorescence image of a single HeLa cell after the FND uptake. An enlarged view of the fluorescence spots (denoted by “1” and “2”) with diffraction-limited sizes (FWHM ≈ 500 nm) is shown in Inset. The separation between these two particles is ≈1 μm. (C) Intensity profile of the fluorescence image along the line drawn in B Inset. (C Inset) Integrated fluorescence intensity (after subtraction of the signals from cell autofluorescence and background fluorescence from the microscope slides) as a function of time for particle “1.” The signal integration time was 0.1 s. No sign of photobleaching was detected after continuous excitation of the particle for 20 min.