TY - JOUR
T1 - Enhanced Ion Yields Using High Energy Water Cluster Beams for Secondary Ion Mass Spectrometry Analysis and Imaging
AU - Sheraz, Sadia
AU - Tian, Hua
AU - Vickerman, John C.
AU - Blenkinsopp, Paul
AU - Winograd, Nicholas
AU - Cumpson, Peter
N1 - Funding Information:
We thank James Hood and Michael Foster for assistance with maintenance of ToF-SIMS and Professor Ian W. Fletcher for general advice and assistance in the Newcastle ToF-SIMS laboratory. The ToF-SIMS instrument at Newcastle University was purchased, in part, under an instrument package funded by EPSRC capital funding grant EP/K022679/1. The work at Pennsylvania State University was supported by NIH grants 5R01GM113746-21 and U54GM103529-08. The tissue samples were generously provided by Prof. Valerian E. Kagan, Prof. Hulya Bayir and Dr. Louis J. Sparvero in University of Pittsburgh. We thank Dr. Dan Graham and Dr. Sebastiaan Van Nuffel for the help with z -correction of HeLa cell 3D imaging.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/5/28
Y1 - 2019/5/28
N2 - 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 C60 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%CO2, and pure CO2. 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.
AB - 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 C60 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%CO2, and pure CO2. 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.
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U2 - 10.1021/acs.analchem.9b01390
DO - 10.1021/acs.analchem.9b01390
M3 - Article
C2 - 31136149
AN - SCOPUS:85069948530
VL - 91
SP - 9058
EP - 9068
JO - Analytical Chemistry
JF - Analytical Chemistry
SN - 0003-2700
IS - 14
ER -