ATOMIC AND MOLECULAR IMAGING AT THE SINGLE-CELL LEVEL WITH TOF-SIMS

A complete cold chain freeze-fracture methodology has been developed t o test the feasibility of using time-of-flight secondary ion mass spec trometry (TOF-SIMS) imaging for the molecular analysis of frozen hydra ted biological samples. Because the technique only samples the first f ew monolayers of a sample, water on the surface of a sample can be a m ajor source of interference. This problem can be minimized by placing a cold trap (fracture knife and housing at -196 degrees C) near the fr actured sample that is held at a warmer temperature (-97 to -113 degre es C). This results in removal of surface water and prevents condensat ion on the surface. Although this approach is effective, it has been f ound that sample warming needs to be carefully controlled due to the v olatility of other matrix molecules and the morphological effects impa rted onto the cell surface during drying. By utilizing the above handl ing technique, it has been possible to demonstrate for the first time that TOF-SIMS imaging technology can be used to obtain images of molec ular species across a cell surface with a submicrometer ion probe beam . images of small hydrocarbons and the deliberately added dopants DMSO and cocaine have been obtained with TOF-SIMS of the single-cell organ ism Paramecium.