Fundamental Mass Spectrometry Measurements of Electrosprayed and Matrix-Assisted Laser Desorbed Ions Using an Improved Superconducting Tunnel Junction Detector

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Professor Mark E. Bier and his students at Carnegie Mellon University are supported by the Chemical Measurement and Imaging (CMI) Program of the Division of Chemistry at the NSF to conduct fundamental studies targeting improved detectors for mass spectrometry (MS, a major tool for characterizing chemicals and biochemicals). Recent advances in data and detector technologies have enabled improvements in both the speed of response and energy resolution attainable when detecting ions during MS analysis. The Bier group is investigating whether measurement of the energy deposited when an ion impacts a detector can be related to the structure of the ion - information critical for understanding how molecules function. This could enable, for example, improved chemical analysis of macromolecular complexes such as virus particles and synthetic nanoparticles. Possible applications span many disciplines, including chemistry, biology, physics, polymer science, medicine and materials science, making the new detector potentially attractive for commercialization. Students involved are exposed to multidisciplinary research, including training in low-temperature physics at Lawrence Livermore National Laboratory. To enable these gas phase ion chemistry measurements, superconducting tunnel junction (STJ) cryodetectors are being improved by increasing the size and number of pixels, resulting in a 10X larger detection area. Both tantalum-STJs and niobium-STJs are being investigated. The detectors are being combined with advanced high-speed electronics to improve arrival time and energy measurements, and tested on two mass spectrometers: a time-of-flight analyzer equipped with matrix-assisted laser desorption ionization (MALDI) and a high m/z ion trap equipped with both MALDI and electrospray ionization (ESI). This should enable generation of mass spectra based on metastable fragmentation. The research is exploring whether the energy response has additional analytical utility in the measurement of shape (e.g., of native proteins) and density (e.g., for gold nanoparticles). The improved energy resolution of STJs and their ability to analyze larger macromolecules could result in a paradigm shift for MS measurements, especially in the fields of polymer and small and large nanoparticle research. New fundamental knowledge about ESI and MALDI should ensue, providing better insight into the respective high m/z limits.