Nanostructure-Dependent Signal Intensity in Through-Hole Porous Alumina Membranes for Mass Spectrometry Imaging

Area of Science:

• Analytical Chemistry
• Materials Science
• Spectroscopy

Background:

• Matrix-assisted laser desorption/ionization (MALDI) is effective for high-molecular-weight compounds but suffers from matrix-derived interference peaks in the low-molecular-weight range.
• Surface-assisted laser desorption/ionization (SALDI) provides a matrix-free alternative, simplifying sample preparation and improving reproducibility.
• Anodic porous alumina membranes (APAMs) have been developed as substrates for SALDI, with potential for mass spectrometry (MS) imaging.

Purpose of the Study:

• To investigate the impact of APAM surface nanostructural properties on signal intensity in MS imaging.
• To identify optimal APAM fabrication conditions for enhanced signal-to-noise ratio (SNR) in SALDI imaging.

Main Methods:

• APAMs were fabricated using oxalic, malonic, and malic acid electrolytes, yielding varied hole diameters (D_h), interhole distances (D_int), and open area ratios (OAR).
• Mass spectrometry (MS) analysis was performed on droplet samples applied to the APAMs.
• MS imaging was conducted on 20-μm-thick mouse brain sections to evaluate the SNR of different APAMs.

Main Results:

• Fabricated APAMs exhibited D_h from 24-419 nm, D_int from 100-625 nm, and OAR from 5%-46%.
• Signal intensity, at constant OAR, increased with D_int in the order of 100, 625, and 270 nm.
• The optimal condition for the highest SNR was D_h/D_int = 131/270 nm. APAMs with D_h < 84 nm and OAR < 10% showed reduced signal intensity.

Conclusions:

• Specific APAM fabrication parameters were identified to maximize the SNR for SALDI imaging.
• SALDI imaging utilizing APAMs fabricated under optimized conditions offers a promising technique for low-molecular-weight analysis.
• This approach is suitable for applications in materials science and metabolomics due to the absence of interference peaks.