Developments in molecular SIMS depth profiling and 3D imaging of biological systems using polyatomic primary ions

Area of Science:

• Analytical Chemistry
• Surface Science
• Biophysics

Background:

• Mass spectral imaging holds significant potential for biological discovery by combining chemical specificity with spatial analysis.
• Current limitations in molecular secondary ion mass spectrometry (SIMS) imaging include low ion yields and the need to sacrifice lateral resolution for sufficient signal.
• Metal cluster ion beams have improved yields but still operate under static limits, with molecular species yields often below 20 counts from 1 µm pixels.

Purpose of the Study:

• To review the potential of polyatomic primary ions for advancing molecular SIMS imaging.
• To explore new instrumental approaches for overcoming limitations in current Time-of-Flight SIMS (ToF-SIMS) instruments.
• To highlight prospects and continuing challenges in sub-micron molecular imaging and depth profiling.

Main Methods:

• Application of polyatomic primary ions with low damage cross-sections for molecular SIMS imaging.
• Utilizing voxels instead of pixels to enhance dynamic signal range in 2D imaging.
• Development of new instrumental directions enabling a direct current (dc) primary beam for ToF-SIMS.

Main Results:

• Polyatomic ions offer a new approach to molecular SIMS imaging, enabling analysis of wider chemistry within sub-micron areas and as a function of depth.
• Recent data on cell and tissue analysis suggest the prospect of improved sub-micron chemical accessibility.
• New instrumental developments show promise for realizing the full capabilities of polyatomic ion beams in SIMS.

Conclusions:

• Advancements in polyatomic ion beams and instrumentation offer significant prospects for high-resolution molecular SIMS imaging and 3D analysis.
• Challenges remain, including low ionization efficiency and matrix effects, which require further investigation.
• Future developments aim to overcome the limitations of pulsed ToF-SIMS, improving analysis times and spatial resolution.