We propose to develop a rapid method for sequencing single-stranded DNA oligomers and polypeptides by reflecting time-of-flight mass spectrometry, using laser desorption, laser ionization, and laser controlled fragmentation. The desorption of DNA segments that have been deposited in a frozen solution or on a solid substrate will be studied by pulsed infrared (IR) and ultraviolet (UV) laser desorption. Desorbed molecules that are neutral in charge will be ionized above the surface by a vacuum ultraviolet (VUV) laser beam, resulting in single-photon ionization; an alternative approach to be compared will be the use of UV laser light, resulting in multiple-photon ionization. Variable fragmentation with an additional laser beam will be investigated as a function of this laser's wavelength, power density, and temporal relationship to the ionizing laser for greatest control in obtaining simple and reliable fragmentation patterns for sequence assignment. The influence of the desorption laser parameters on fragmentation also will be examined.The experiments are designed to decouple as much as possible the three processes of desorption, ionization, and fragmentation for maximum control of these processes. This technology may be capable of sequencing >10(6) nucleotides per day per machine.
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