Comparing pulsed and continuous laser-induced acoustic desorption (LIAD) as sources for intact biomolecules

A major obstacle to the gas-phase study of larger (bio)molecular systems is the vaporisation step, that is, the introduction of intact sample molecules into the gas-phase. A promising approach is the use of laser-induced acoustic desorption (LIAD) sources, which have been demonstrated using both nanosecond pulsed and continuous desorption lasers. We directly compare here both approaches for the first time under otherwise identical conditions using adenine as a prototypical biological molecule, and study the produced molecular plumes using femtosecond multiphoton ionisation. We observe different desorption mechanisms at play for the two different desorption laser sources; however, we find no evidence in either case that the desorption process leads to fragmentation of the target molecule unless excessive desorption energy is applied. This makes LIAD a powerful approach for techniques that require high density and high purity samples in the gas-phase, such as ultrafast dynamics studies or diffraction experiments. Graphic abstract