Detection of biomolecules on surfaces using ion-beam-induced desorption and multiphoton resonance ionization

Abstract

Multiphoton resonance ionization (MPRI) has been combined with ion-beam-induced desorption to examine a set of thermally labile biological molecules present on surfaces. Specifically, we have examined films of adenine and beta-estradiol, molecules with a rigid skeletal backbone. In both of these cases, molecular ions could be produced efficiently without cooling the neutral molecules into their ground vibrational state. We have also studied other more fragile molecules such as tryptamine, tryptophan, phenylalanine, and serotonin. The base peak in the mass spectra of these molecules is fragment ions formed by losses of the amine side chains. Even with this fragmentation, however, it is possible to achieve sensitivity limits that are many orders of magnitude greater than for secondary ion mass spectrometry, without preparing the samples in special matrices. For serotonin, detection limits of 40 fmol on the surface of a silicon target are achievable. The results also yield a linear relation between the serotonin base fragment ion intensity and the known surface concentration.

Laser: a Tool for Optimization and Enhancement of Analytical Methods

“…In order to ionize common organic compounds, a variety of laser sources can be used, fragmentation of the large molecule is believed to be more likely than release of a free Photoionization is not, however, efficient in ionization of 67,68,71,[72][73][74][75][76][80][81][82][83][84][85][86] Recombination of the ion pair created by ionization and 78,79 193-nm radiation is an interesting choice of wavelength for photoionization.…”

Postionization of molecules desorbed from surfaces by keV ion bombardment with femtosecond laser pulses

“…[2][3][4] However, these lasers are limited to repetition rates of less than 100 Hz, which makes the use of these lasers in imaging experiments problematic. Advances in laser technology have made it possible to obtain high power sub-100 femtosecond laser pulses at kHz repetition rates.…”

“…[2][3][4] This approach has proven successful in the surface analysis of desorbed atomic and molecular species, with detection limits achieved in the low ppt levels when incorporating resonance enhanced multiphoton ionization. 5 Fragmentation, however, is a concern when photoionizing molecular systems through a multiphoton ionization (MPI) process.…”

Imaging of Polycyclic Aromatic Hydrocarbons by Means of Sputtered Neutrals Mass Spectrometry Using a Diode-pumped Solid-State Laser

“…Although TOF-SIMS has excellent sensitivity for aliphatic hydrocarbons and fatty acids, it is difficult to clearly detect the molecular ion peak for polycyclic aromatic hydrocarbons (PAHs). 1 A technique named laser-SNMS 2 (laser post-ionization sputtered neutral mass spectrometry) utilizes a laser to promote an electron to some excited states of atoms or molecules. When the laser wavelength coincides with the excitation energy of a certain species, the ionization yield is resonantly enhanced.…”