Production of nanoscopic metal labels for electron microscopy: Specific detection of target DNA

The simultaneous detection of multiple target biomolecules with scanning electron microscopy is difficult due to the lack of a suitable label set. Unlike the fluorescence dyes used for fluorescence microscopy, there are no readily available labels that can be distinguished. We propose using nanoscopic metal particles of different element species as labels because various metals scatter electrons differently, making them distinguishable in backscattered electron images. We have developed a universal method for forming such metal particles. They are prepared by thermal deposition of a metal onto surface-adsorbed latex spheres having the shape of a half-shell, creating exposed metal and latex surfaces. Either surface can be selectively modified with probe DNA to enable the half-shell label to react with target DNA. Half-shells prepared with different metals were clearly distinguished in the backscattered electron observation mode of a field emission scanning electron microscope. Target DNA was detected with these half-shells, indicating that this half-shell labeling can be used for simultaneous detection of specific target biomolecules.