Secondary Ion MS Imaging of Lipids in Picoliter Vials with a Buckminsterfullerene Ion Source

Abstract

Investigation of the spatial distribution of lipids in cell membranes can lead to an improved understanding of the role of lipids in biological function and disease. Time-of-flight secondary ion mass spectrometry is capable of molecule-specific imaging of biological molecules across single cells and has demonstrated potential for examining the functional segregation of lipids in cell membranes. In this paper, standard SIMS spectra are analyzed for phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine, phosphatidylinositol, cholesterol, and sulfatide. Importantly, each of the lipids result in signature mass spectral peaks that allow them to be identified. These signature peaks are also useful for imaging experiments and are utilized here to simultaneously image lipids on a micrometer scale in picoliter vials. Because the low secondary ion signal achieved for lipids from an atomic primary ion source makes cell-imaging experiments challenging, improving signal with cluster primary ion sources is of interest. Here, we compare the secondary ion yield for seven lipids using atomic (Ga+ or In+) ion sources and a buckminsterfullerene (C60+) primary ion source. A 40-1000-fold improvement in signal is found with C60+ relative to the other two ion sources, indicating great promise for future cellular imaging applications using the C60+ probe.

Lipid mapping in human dystrophic muscle by cluster-time-of-flight secondary ion mass spectrometry imaging

“…For the human samples, the PI fragment ions were present in all mass spectra, together with ions at m/z 259.0 and 299.0 (two other PI characteristic fragments) (34) and with the C20:4 ion at m/z 303.2 (Fig. 7B).…”

Surface analysis of lipids by mass spectrometry: More than just imaging

“…Cluster ion sources generate a significant increase in the amount of material ejected from the surface upon projectile impact, thereby providing more material for the analysis. In addition, they also lead to higher ion yields, reduced surface damage and enhanced observation of intact lipid ions relative to ionic fragments [158,159,162,163]. In the case of C 60 + , the reduced surface damage allows a stable, prolonged ion signal at a fixed sampling position and enhanced signal with acquisition using higher ion fluences, thereby allowing analysis of a larger portion of the sample area [163].…”

“…compared the intensity of lipid-related ions obtained from C 60 + and Ga + ion sources and found 70-1000 fold signal enhancement for the C 60 + ion source with the degree of enhancement dependant on lipid class [162]. In another study, rat brain tissue was analyzed using both Au + and C 60 + ion sources [163].…”

Ultra-High Vacuum Surface Analysis Study of Rhodopsin Incorporation into Supported Lipid Bilayers

“…found could also originate from the lipid head groups, but are found at much higher intensities in proteins compared to lipids. 39 Fragments originating from the lipid tails, on the other hand, loaded more strongly with polymerized bilayers that lacked Rho (Figure 4). These results are consistent with the XPS results discussed above.…”