Recently, we performed the first time-resolved imaging of the MALDI (Matrix-Assisted Laser Desorption and Ionization) process. MALDI is a powerful technique to accurately measure the masses of heavy molecules. In MALDI, a heavy biomolecule (such as a protein, or fragment of DNA) is gently laser-desorbed inside a vacuum chamber. To accomplish this, a very small number of biomolecules are first mixed with an organic liquid which is allowed to dry into a crystalline matrix. The sacrificial crystal matrix absorbs the laser energy, heats and vaporizes, ejecting the biomolecule into the gas-phase. During this process, some of the matrix and some of the biomolecules become ionized. The exact mechanism is not known. These ionized molecules are accelerated down a time-of-flight mass spectrometer. From their flight time, their masses can be measured accurately.
In order to optimize the technique, the fraction of material which becomes ionized should be increased and the dynamics of the vaporization process must be determined in order to compensate for the initial velocities and trajectories of the ejecta down the time-of-flight mass spectrometer.
In our recent experiments, we used laser-induced fluorescence imaging of both: (1) the matrix and (2) DNA-fragments which had a fluorescent dye attached. In this way, we could see the influence of the matrix expansion on the heavy biomolecule. We found that the plumes of heavy biomolecules expanded in very narrow trajectories which "sharpened" as they expanded. This "plume sharpening" effect had never been observed before. We developed a theory which describes the dimensions of the plumes of both the matrix and the heavy biomolecules for arbitrary masses.
This work was recently accepted for publication in Physical Review Letters.
"Imaging of Vapor Plumes Produced by Matrix Assisted Laser Desorption: A New Plume Sharpening Effect" A.A. Puretzky, D.B. Geohegan, G. B. Hurst, M. V. Buchanan and B. Luk'yanchuk, Phys. Rev. Lett. (in press, accepted 5/1999).
(see also)
"Gas-Phase Diagnostics and LIF-Imaging of 3-Hydroxypicolinic Acid MALDI-Matrix Plumes," A.A. Puretzky and D.B. Geohegan, Chem. Phys. Lett. 286, 425 (1998).(1998).
"LIF-Imaging and Gas-Phase Diagnostics of Laser Desorbed MALDI Matrix Plumes," A.A. Puretzky and D.B. Geohegan, Appl. Surf. Sci. 127/129, 151 (1998) (1998).
