MALDI mass spectrometry imaging in microscope mode with infrared lasers: bypassing the diffraction limits

Area of Science:

• Analytical Chemistry
• Biophysics
• Microscopy

Background:

• Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a powerful technique for analyzing biomolecules in tissues.
• Achieving high spatial resolution in MSI is crucial for detailed biological investigations.
• Current methods often rely on external matrices, which can limit resolution or introduce artifacts.

Purpose of the Study:

• To demonstrate the feasibility of using intrinsic water in biological tissues as a matrix for infrared MALDI-MSI.
• To achieve spatial resolutions below the diffraction limit of infrared optics.
• To evaluate the performance of a stigmatic ion-optical setup for high-resolution MSI.

Main Methods:

• Infrared matrix-assisted laser desorption/ionization coupled with microscope mode mass spectrometry imaging.
• Utilized stigmatic ion optics with ~70x magnification and a time-of-flight mass spectrometer.
• Employed a pixelated detector for simultaneous recording of ion arrival time and impact position.
• Benchmarked the system using a dried-droplet sample of 2,5-dihydroxybenzoic acid (DHB) and peptides.
• Applied the technique to frozen cryo-sections of biological tissues, using endogenous water as the matrix.

Main Results:

• Established a spatial resolving power of 9.8 μm, surpassing the optical diffraction limit of 14 μm for the setup.
• Successfully imaged biological tissues by exploiting endogenous water as the matrix.
• Principal component analysis clearly distinguished between different tissue regions based on MS imaging data.

Conclusions:

• Intrinsic water can effectively serve as a matrix for infrared MALDI-MSI, enabling sub-diffraction limit spatial resolution.
• The developed light- and ion-optical setup provides high mass spectrometric performance for biological tissue analysis.
• This technique offers a promising approach for high-resolution molecular imaging of biological samples.