The long term objective of the proposed project is to develop instrumentation for rapid and accurate DNA sequencing. The approach is to use time of flight (TOF) mass spectrometry to size order DNA fragments generated by standard Sanger/Maxim-Gilbert methodologies. A novel approach will be used to achieve sample ionization. An intense laser pulse will volatilize individual aqueous droplets containing the DNA fragment mixture. The droplet disintegration event will propel DNA molecular ions into the acceleration region of the TOF mass spectrometer. This methodology, if successful, would provide the means to optimize sample introduction and enhance the resolution of the TOF mass measurement. To demonstrate the feasibility of this approach, we propose to: 1. Develop a droplet generator based ink jet technology that can operate in the vacuum environment of a mass spectrometer. Droplets approximately 25 micromoles in diameter would be produced on demand from aqueous solutions and directed into the TOF Mass Spectrometer ion source. 2. Demonstrate the interaction of a focused infrared laser beam pulse with aqueous droplets to produce sample ions. Laser power levels between that required for the onset of droplet evaporation and that required for plasma formation will be explored. In this range, it should be possible to achieve shock wave disintegration of droplets resulting in intact molecular ions on a time scale compatible with TOF mass measurements. 3. Obtain TOF mass spectra of DNA fragments from aqueous droplets. After the various experimental parameters have been defined for successful analysis of synthetic oligonucleotides, the analysis of larger DNA fragments and fragment mixtures will be attempted. For the system described, an ultimate DNA sequencing rate of 500 base- pairs/second is predicted which would ensure that the time to analyze DNA fragments would never be the rate limiting step for the human genome sequencing operation.
