Peptide Mass Spectra from Micrometer-Thick Ice Films Produced with Femtosecond Pulses

Area of Science:

• Analytical Chemistry
• Spectroscopy

Background:

• Matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) typically require matrix or substrate modification for analyte detection.
• Detecting low concentrations of peptides in aqueous solutions presents analytical challenges.

Purpose of the Study:

• To present a novel cryogenic mass spectrometry protocol for attomole-level peptide detection.
• To investigate the effects of temperature, substrate, and laser wavelength on signal generation.

Main Methods:

• Utilized femtosecond laser pulses for desorption/ionization without matrix or substrate modification.
• Systematically varied temperature (-140 to 0 °C), substrate composition, and irradiation wavelength (513 and 1026 nm).
• Analyzed bradykinin signal onset and fragmentation patterns.

Main Results:

• Optimized protocol showed minor impact of substrate and wavelength on signal intensity.
• Analyte desorption and ionization were complex with increasing temperature and ice film thinning.
• Signal detection improved significantly with ice sublimation above -70 °C, providing robust signals for hours.
• Fragmentation patterns were consistent across different wavelengths.

Conclusions:

• Femtosecond mass spectrometry offers a promising method for analyzing peptides and small organic molecules (up to 2.5 kDa) in aqueous solution.
• The developed cryogenic protocol enables highly sensitive detection without traditional matrix or substrate enhancements.
• Temperature-induced ice sublimation is crucial for achieving intense and stable signals.