Enhanced Ion Yields Using High Energy Water Cluster Beams for Secondary Ion Mass Spectrometry Analysis and Imaging

Abstract

Previous studies have shown that the use of a 20 keV water cluster beam as a primary beam for the analysis of organic and bio-organic systems resulted in a 10−100 times increase in positive molecular ion yield for a range of typical analytes compared to C 60 and argon cluster beams. This resulted in increased sensitivity to important lipid molecules in the bioimaging of rat brain. Building on these studies, the present work compares 40 and 70 keV water cluster beams with cluster beams composed of pure argon, argon and 10%CO 2 , and pure CO 2 . First, as previously, we show that for E/nucleon about 0.3 eV/nucleon water and nonwater containing cluster beams generate very similar ion yields, but below this value, the water beams yields of BOTH negative and positive "molecular" ions increase, in many cases reaching a maximum in the <0.2 region, with yield increases of ∼10−100. Ion fragment yields in general decrease quite dramatically in this region. Second, for water cluster beams at a constant E/nucleon, "molecular" ion yield increases with beam energy and hence cluster size due to increased sputter yield (ionization probability is constant). Third, as a consequence of the increased ion yield and the improved focusability using high-energy cluster beams, imaging in the 1 μm spatial resolution region is demonstrated on HeLa cells and rat brain tissue, monitoring molecules that were previously difficult to detect with other primary beams. Finally, the suggestion that the secondary ion emission zone has quasi-aqueous character seems to be sustained.

(CO2)n+, (H2O)n+, and (H2O)n+ (CO2) gas cluster ion beam secondary ion mass spectrometry: analysis of lipid extracts, cells, and Alzheimer’s model mouse brain tissue

“…One approach suggested for reaching this goal is through the use of reactive cluster ion beams. For biological analysis, several proof of principle papers have been published highlighting the potential of using water cluster beams of the type (H 2 O) n + [33][34][35][36][37]. The use of the water cluster was initially envisaged as a proton source that might aid the formation of [M + H] + ions due to the interaction with the primary particle with the sample and the target analyte during the ejection process.…”

Direct Mapping of Phospholipid Ferroptotic Death Signals in Cells and Tissues by Gas Cluster Ion Beam Secondary Ion Mass Spectrometry (GCIB‐SIMS)

“…The combination of the H 2 O cluster with high kinetic energy, ca. 70 keV, has led to both increased sensitivity and spatial resolution [7] . This has provided us with an advantage in attempts to image very low abundance oxidized phospholipid species acting as signaling molecules at the single cell level.…”

Imaging mass spectrometry: a new way to distinguish dermal contact from administration of cocaine, using a single fingerprint

“…32 The primary ion beam used was a 70 kV gas cluster ion beam fitted with a water source. 30,33 The water source replaces a standard gas cluster ion beam (GCIB) source to enable both wet and dry gas sources to be used. A 70 kV (H 2 O) 29 000 + beam was used for this study with a current of 14 pA, focused to a spot size of 10 µm with a duty cycle of 50%.…”

“…Recent advances in the ion sources used in ToF-SIMS systems have led to the development of water cluster SIMS, which offers enhanced sensitivity to intact organic molecules. 30,31 In this work, we apply MALDI, DESI, ToF-SIMS and water cluster SIMS imaging to fingerprint samples collected from drug users as well as from participants (non-drug users) who were asked to handle cocaine. We show how mass spectrometry imaging (MSI) of fingerprints can help distinguish between administration and contact with cocaine.…”