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

Area of Science:

• Surface science and analytical chemistry
• Biophysics and bioimaging

Background:

• Previous research demonstrated that 20 keV water cluster beams increased molecular ion yield by 10-100x for organic and bio-organic systems compared to C60 and argon cluster beams.
• This led to enhanced sensitivity for lipid molecule detection in rat brain bioimaging.

Purpose of the Study:

• To compare the performance of higher energy (40 and 70 keV) water cluster beams against pure argon, argon/CO2, and pure CO2 cluster beams.
• To investigate the effect of beam energy and cluster size on ion yields and imaging capabilities.
• To further evaluate the quasi-aqueous character of the secondary ion emission zone.

Main Methods:

• Comparative analysis of ion yields using water cluster beams (40 and 70 keV) versus non-water cluster beams (argon, argon/CO2, CO2).
• Investigation of ion yields at varying energy per nucleon (E/nucleon) values, particularly below 0.3 eV/nucleon.
• Demonstration of high-resolution (1 μm) bioimaging on HeLa cells and rat brain tissue using optimized water cluster beams.

Main Results:

• Below 0.3 eV/nucleon, water cluster beams significantly increase both positive and negative molecular ion yields (∼10-100x), while fragment ion yields decrease.
• For water cluster beams, molecular ion yield increases with beam energy and cluster size at a constant E/nucleon.
• High-resolution imaging (1 μm) was achieved, enabling detection of previously difficult-to-monitor molecules in biological tissues.

Conclusions:

• Higher energy water cluster beams offer superior performance for molecular analysis and bioimaging compared to other cluster beams.
• The findings support the hypothesis that the secondary ion emission zone exhibits quasi-aqueous characteristics.
• This technique advances the sensitivity and resolution for analyzing complex organic and biological systems.