Ultrathin cryosections: an important tool for immunofluorescence and correlative microscopy.

Here we show that ultrathin cryosections of placental tissue can be used as a substrate in immunofluorescence experiments. A high degree of spatial resolution can be achieved in these preparations because there is essentially no out-of-focus fluorescence. Therefore, immunofluorescence microscopy using ultrathin cryosections provides a very useful method for determining the precise subcellular localization of antigens in tissues. In addition, ultrathin cryosections of placenta also serve as a substrate for correlative immunofluorescence and immunoelectron microscopy using FluoroNanogold as the detection system. In correlative microscopy, the exact same structures in the same ultrathin section were observed by both fluorescence and electron microscopy. Using a particle counting procedure and electron microscopy, we compared the labeling obtained with colloidal gold and FluoroNanogold and found a higher number of particles with silver-enhanced FluoroNanogold than with colloidal gold.