The image process for enhancing the contrast of AuNPs. (a) The dark-field optical image of a CL1-0 cell with 45-nm-AuNPs observed by a 60× oil lens and a color CCD. The AuNPs show orange colors in the dark-field image. There are white brighter regions appeared in the cell due to the scattering from large organelles. (b) The monochromatic image of the yellow component, (c) The monochromatic image of the blue component. Compared both images, the AuNPs have a higher contrast in the yellow image. The organelles is brighter in the blue image. (d) The combination of the Y and B images by using the (Y-B) calculations. The image process results in an image with bright AuNP spots and dark organelles. The unit is μm.