In vitro samples, e.g. proteins in buffer solutions (at a protein concentration of about 0.1 mg.ml-1) are flash-frozen in thin layers prior to tomography. When analyzing the 3-D results, the specific proteins or protein complexes are identified by molecular size, characteristically shaped features, other marker proteins, or comparative structural data. Individual protein objects are selected from the reconstructed sample volume and studied in detail (see tomogram of IgG molecule below).
