Pulse-heating ionization for protein on-chip mass spectrometry

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Materials Science

Background:

• Miniaturization of mass spectrometry systems is crucial for portable and on-site analysis.
• Conventional protein ionization methods often require complex instrumentation like lasers or high voltages.

Purpose of the Study:

• To develop and demonstrate an on-chip pulse-heating ionization source for protein analysis.
• To achieve protein ionization using only thermal energy applied to a solid-phase sample.

Main Methods:

• Fabrication of a platinum/chromium (Pt/Cr) microheater on a silicon substrate.
• Coupling the microheater with a time-of-flight mass filter.
• Ionization of bovine serum albumin (BSA) using thermal energy and various matrices (2,5-dihydroxybenzoic acid, 2,5-dihydroxyacetophenone, sinapic acid).

Main Results:

• Successful ionization of singly and multiply charged bovine serum albumin (BSA) ions.
• Determination of the energy density required for singly charged BSA ion detection (1.65 × 10^-2 μJ/μm^2).
• Differential protein charge state generation observed with different matrices: 2,5-dihydroxyacetophenone favored multiply charged ions, while sinapic acid yielded low m/z peaks.

Conclusions:

• The developed on-chip pulse-heating source is effective for protein ionization in miniaturized mass spectrometry.
• Thermal energy-based ionization offers a simplified alternative to laser or high-voltage methods.
• Matrix selection significantly influences the charge state distribution of ionized proteins.