• confocal microscopy;
  • submicroscopic detection;
  • magnetite

Light microscopy and transmission electron microscopy work at such different scales that some components of cells may be too small to detect using light microscopy but too dispersed among cells within tissues to be discovered using electron microscopy. We have used reflectance mode confocal laser scanning microscopy to detect single-domain magnetite crystals in both live and resin-embedded preparations of magnetotactic bacteria. We show that reflections from bacterial cells are uniquely associated with the magnetite, which underpins the magnetotactic response of the bacteria. En bloc viewing shows that relatively large volumes of material can be searched with sufficient resolution to enable detection of submicroscopic particles. The techniques reported here may be of interest to others wishing to detect submicroscopic objects dispersed in large volumes of tissue.