Multimodal Imaging of Chemically Fixed Cells in Preparation for NanoSIMS

In this work, we have employed time-of-flight secondary ion mass spectrometry (ToF-SIMS) to image chemically fixed adrenal cells prepared for transmission electron microscopy (TEM) and subsequent high-spatial-resolution NanoSIMS imaging. The sample fixation methodology preserves cell morphology, allows analysis in the ultrahigh vacuum environment, and reduces topographic artifacts, thus making these samples particularly favorable for ToF-SIMS analysis. ToF-SIMS imaging enables us to determine the chemistry and preservation capabilities of the chemical fixation as well as to locate specific ion species from OsO₄. The OsO₄ species have been localized in lysosomes of cortical cells, a type of adrenal cell present in the culture. NanoSIMS imaging of the ¹⁹⁰Os¹⁶O^- ion species in cortical cells reveals the same localization as a wide range of OsO₄ ions shown with ToF-SIMS. Even though we did not use during NanoSIMS imaging the exact Os_xO_y^- ion species discovered with ToF-SIMS, ToF-SIMS allowed us to define the specific subcellular features in a high spatial resolution imaging mode. This study demonstrates the possibility for application of ToF-SIMS as a screening tool to optimize high-resolution imaging with NanoSIMS, which could replace TEM for localization in ultrahigh resolution imaging analyses.