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Dr. John J. Brady

Staff Scientist
Signature Science LLC


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Area of Expertise: mass spectrometry, femtosecond lasers, nonlinear optics, Raman spectroscopy, laser desorption, electrospray ionization
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Summary
My Ph.D. concerned the design and implementation of a state-of-the-art ambient trace analysis technique known as laser electrospray mass spectrometry. This novel technique utilizes an intense, nonresonant, femtosecond laser pulse to transfer nonvolatile, fragile molecules into the gas phase from various substrates. The vaporized analyte is subsequently captured, solvated and ionized in an electrospray plume enabling mass analysis. Laser electrospray mass spectrometry is capable of analyzing samples in the liquid or solid states, mass spectral imaging of adsorbed molecules and remote detection of low vapor pressure analytes. Experiments with biomolecules and pharmaceuticals, such as vitamin B12 and oxycodone have demonstrated that the nonresonant, femtosecond laser pulse allows for coupling into and vaporization of all molecules. This implies that sample preparation (elution, mixing with matrix, and choosing samples with a particular electronic or vibrational transition) is not necessary, thus creating a universal mass analysis technique.
Investigations using low vapor pressure molecules, such as lipids and proteins, led to the discovery that unfragmented molecules are transferred into the gas phase via a nonthermal mechanism. The “soft” vaporization of molecules using nonresonant, femtosecond laser pulses allows for protein to be transferred from the condensed phase into the gas phase without altering the molecule’s conformation, enabling ex vivo conformational analysis. In addition, the laser electrospray mass spectrometry technique has allowed for the vaporization, mass analysis and classification of trace amounts of nitro-based, peroxide-based, organic-based and inorganic-based explosives from a variety of surfaces including sand and metal. The vaporization of unfragmented explosive molecules from a surface facilitates the identification of the explosive, reducing the probability of false positives and false negatives.
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