Colloidal palladium particles of different shapes for electron microscopy labeling.

The immunogold technique is a valuable method for labeling cellular macromolecules. However, multiple labeling using colloidal gold (cAu) nanoparticles of different sizes presents certain drawbacks; namely, as particle size increases, there is a decreased labeling efficiency and diminished spatial resolution with respect to the locations of labeled epitopes. Both concerns also limit the utility of heavy metal particles for comparative analysis of labeling densities. To minimize the variables due to differential labeling efficiencies, the best solution would be to conduct multiple labeling with particles of similar size. Consequently, some parameter other than size is necessary to distinguish each label type. In this study, we report the synthesis of colloidal palladium (cPd) nanoparticles of similar size but having two distinct shapes, umbonate and faceted, which are readily distinguishable from spherical colloidal gold particles. Their utility and fidelity as labels using a human platelet whole-mount model is also demonstrated.