Investigating the effect of temperature on depth profiles of biological material using ToF-SIMS

In this study we examine the depth profiles of two bio-materials, an amino acid (arginine) and a polypeptide (Gly-Gly-Tyr-Arg), to observe the effects of temperature on sample analysis with time of flight secondary ion mass spectrometry (ToF-SIMS). The samples were prepared as dried droplet films on silicon and were analyzed at room temperature (300 K) and at cryogenic temperatures (100 K). Under cryogenic analysis conditions, molecular ion yields at the steady state increased by factors of 1.8 and 5 for arginine and the tetrapeptide respectively compared to analysis at room temperature. Increases are also observed in arginine dimer and trimer ion formation by factors of 6 and 5 respectively, while the lower mass fragment ions investigated did not change in intensity by more than 30%. Further analysis of the results show that the decrease in the steady state ion yield with primary ion fluence at 300 K is reduced when analyzed at 100 K, indicating a decrease in chemical damage. These results suggest that analysis under cryogenic conditions provides several benefits for the analysis of biological compounds and hence for 3D molecular imaging of cells and tissue. Copyright (C) 2010 John Wiley & Sons, Ltd.