Multiomics Imaging Using High-Energy Water Gas Cluster Ion Beam Secondary Ion Mass Spectrometry [(H2O)n-GCIB-SIMS] of Frozen-Hydrated Cells and Tissue.

Integration of multiomics at the single-cell level allows the unambiguous dissecting of phenotypic heterogeneity at different states such as health, disease, and biomedical response. Imaging mass spectrometry holds the promise of being able to measure multiple types of biomolecules in parallel in the same cell. We have explored the possibility of using water gas cluster ion beam secondary ion mass spectrometry [(H2O)n-GCIB-SIMS] as an analytical tool for multiomics assay. (H2O)n-GCIB has been hailed as an ideal ionization source for biological sampling owing to the enhanced chemical sensitivity and reduced matrix effect. Taking advantage of 1 µm spatial resolution by using a high-energy beam system, we have clearly shown the enhancement of multiple intact biomolecules up to a few hundredfold in single cells. Coupled with the cryogenic sample preparation/measurement, the lipids and metabolites were imaged simultaneously within the cellular region, uncovering the pristine chemistry for integrated omics in the same sample. We have demonstrated that double-charged myelin protein fragments and single-charged multiple lipids and metabolites can be localized in the same cells/tissue with a single acquisition. Our exploration has also been extended to the capability of (H2O)n-GCIB in the generation of multiple charged peptides on protein standards. Frozen hydration combined with (H2O)n-GCIB provides the possibility of universal enhancement for the ionization of multiple bio-molecules, including peptides/proteins which has allowed "omics" to become feasible in the same sample using SIMS.

Enhancing ion yields in time-of-flight-secondary ion mass spectrometry: a comparative study of argon and water cluster primary beams.

Following from our previous Letter on this topic, this Article reports a detailed study of time-of-flight-secondary ion mass spectrometry (TOF-SIMS) positive ion spectra generated from a set of model biocompounds (arginine, trehalose, DPPC, and angiotensin II) by water cluster primary ion beams in comparison to argon cluster beams over a range of cluster sizes and energies. Sputter yield studies using argon and water beams on arginine and Irganox 1010 have confirmed that the sputter yields using water cluster beams lie on the same universal sputtering curve derived by Seah for argon cluster beams. Thus, increased ion yield using water cluster beams must arise from increased ionization. The spectra and positive ion signals observed using cluster beams in the size range from 1,000 to 10,000 and the energy range 5-20 keV are reported. It is confirmed that water cluster beams enhance proton related ionization over against argon beams to a significant degree such that enhanced detection sensitivities from 1 µm(2) in the region of 100 to 1,000 times relative to static SIMS analysis with Ar2000 cluster beams appear to be accessible. These new studies show that there is an unexpected complexity in the ionization enhancement phenomenon. Whereas optimum ion yields under argon cluster bombardment occur in the region of E/n ≥ 10 eV (where E is the beam energy and n the number of argon atoms in the cluster) and fall rapidly when E/n < 10 eV; for water cluster beams, ion yields increase significantly in this E/n regime (where n is the number of water molecules in the cluster) and peak for 20 keV beams at a cluster size of 7,000 or E/n ∼3 eV. This important result is explored further using D2O cluster beams that confirm that in this low E/n regime protonation does originate to a large extent from the water molecules. The results, encouraging in themselves, suggest that for both argon and water cluster beams, higher energy beams, e.g., 40 and 80 keV, would enable larger cluster sizes to be exploited with significant benefit for ion yield and hence analytical capability.

Enhancing secondary ion yields in time of flight-secondary ion mass spectrometry using water cluster primary beams.

Low secondary ion yields from organic and biological molecules are the principal limitation on the future exploitation of time of flight-secondary ion mass spectrometry (TOF-SIMS) as a surface and materials analysis technique. On the basis of the hypothesis that increasing the density of water related fragments in the ion impact zone would enhance proton mediated reactions, a prototype water cluster ion beam has been developed using supersonic jet expansion methodologies that enable ion yields using a 10 keV (H2O)1000(+) beam to be compared with those obtained using a 10 keV Ar1000(+) beam. The ion yields from four standard compounds, arginine, haloperidol, DPPC, and angiotensin II, have been measured under static+ and high ion dose conditions. Ion yield enhancements relative to the argon beam on the order of 10 or more have been observed for all the compounds such that the molecular ion yield per a 1 µm pixel can be as high as 20, relative to 0.05 under an argon beam. The water beam has also been shown to partially lift the matrix effect in a 1:10 mixture of haloperidol and dipalmitoylphosphatidylcholine (DPPC) that suppresses the haloperidol signal. These results provide encouragement that further developments of the water cluster beam to higher energies and larger cluster sizes will provide the ion yield enhancements necessary for the future development of TOF-SIMS.