Nicholas Winograd

Surface Chemistry and Chemical Imaging of Biomaterials

Professor Winograd and his students are pursuing new ways to learn about the behavior of various molecular surfaces and interfaces. To accomplish this task, surface-sensitive techniques are being developed that yield the molecular composition of the top layers of a solid. These techniques are then applied to the characterization of surfaces with special relevance to biology and materials science.

Mass spectrometry plays a particularly important role in these experiments. Using energetic cluster ion beams, it is possible to desorb thermally labile molecules from almost any type of matrix and to extract the secondary ions into a time-of-flight mass analyzer. Moreover, these ion beams can be focused to a diameter of less than 100 nm such that the desorption occurs from a specific point on the sample. By scanning the beam over an area, molecule specific images are constructed that yield a map of the spatial distribution of a diverse set of molecules with nanometer precision. Research is aimed toward 1) understanding the fundamental aspects of the ion/solid interaction associated with this type of mass spectrometry, 2) seeking out novel schemes to broaden the scope of the measurements, and 3) pursuing science problems that cannot be carried out by other methods, particularly in biologically related fields.  The group has recently discovered that Buckminsterfullerene projectiles have very special properties for molecular desorption and 3-dimensional imaging experiments, and an intense effort is underway to exploit this novel modality.

Fundamental studies are performed on well-defined model systems where it is possible to measure the trajectories of the desorbing neutral molecules in specific vibrational and electronic states. To perform these measurements, a special laser system has been developed that resonantly ionizes the neutral molecules by multiphoton excitation and enables extraction of both velocity and take-off angle information. These data are then compared with molecular dynamics computer simulations performed mainly by Professor Garrison and her students. These experiments are currently being optimized to elucidate the mechanism of desorption induced by cluster ion beams such as C₆₀. The research provides valuable fundamental information about the mechanism of molecular desorption and suggests new experimental configurations to enhance the information content of the measurements.

There are several significant science problems where these techniques are having an impact. The group has a major collaborative effort with the Ewing group aimed toward elucidating the chemical composition of single biological cells. To achieve these measurements, the mass spectrometer is being coupled to a cryogenic system that allows biological cells to be examined using a freeze-fracture technique. The goal is to be able to map the chemical composition inside single cells and to identify the binding location of various small pharmaceutical agents with subcellular spatial resolution. This research requires an intellectual interest in instrumentation, surface science, and biological chemistry.