Mass Spectra and Yields of Intact Charged Biomolecules Ejected by Massive Cluster Impact for Bioimaging in a Time-of-Flight Secondary Ion Microscope.

Impacts of massive, highly charged glycerol clusters (greater than or similar to 10(6) Da, greater than or similar to +/- 100 charges) have been used to eject intact charged molecules of peptides, lipids, and small proteins from pure solid samples, enabling imaging using these ion species in a time-of-flight secondary ion microscope with few-micrometer spatial resolution. Here, we report mass spectra and useful ion yields (ratio of intact charged molecules detected to molecules sputtered) for several molecular species two peptides, bradykinin and angiotensin II; two lipids, phosphatidylcholine and sphingomyelin; Irganox 1010 (a detergent); insulin; and rhodamine B-and show that useful ion yields are high enough to enable bioimaging of peptides and lipids in biological samples with few-micrometer resolution and acceptable signals. For example, several hundred molecular ion counts should be detectable from a 3 X 3 mu m(2) area of a pure lipid bilayer given appropriate instrumentation or tens of counts from a minor constituent of such a layer.