MIT Reports to the President 1998-99
The George Russell Harrison Spectroscopy Laboratory is engaged in research in the field of modern optics and spectroscopy for the purpose of furthering fundamental knowledge of atoms and molecules and pursuing advanced engineering and biomedical applications. Professor Michael S. Feld is Director; Professor Jeffrey I. Steinfeld and Dr. Ramachandra R. Dasari are Associate Directors. An Interdepartmental Laboratory, the Spectroscopy Laboratory encourages participation and collaboration among researchers in various disciplines of science and engineering. Professors Moungi G. Bawendi, Feld, Robert W. Field, Daniel Kleppner, Stephen J. Lippard, Keith A. Nelson, Steinfeld, Toyoichi Tanaka, Steven R. Tannenbaum and Dr. Dasari are core investigators.
The Laboratory operates two laser resource facilities. The MIT Laser Biomedical Research Center (LBRC), a Biotechnology Resource Center of the National Institutes of Health, develops basic scientific understanding, new techniques and technology for advanced biomedical applications of lasers; core, collaborative and outside research are conducted. The National Science Foundation-supported MIT Laser Research Facility (LRF) provides resources for core research programs in the physical sciences for 13 MIT Chemistry and Physics faculty. Information about the equipment and facilities of the LRF and the LBRC can be found in the Spectroscopy Laboratory Researcher's Guide.
RESEARCH HIGHLIGHTS
Professor Field and his associates, Drs. Haruki Ishikawa and Matthew Jacobson, have observed the spectroscopic signature of bond-breaking unimolecular isomerization in HCP and HCCH. The energy level and intensity patterns associated with isomerization are now well specified, and these are accompanied by qualitative changes in the nodal structure of the wavefunctions and bifurcations in the form of the classical mechanical periodic orbits. This seminal result in vibrational spectroscopy and dynamics has become a focus for experiment and theory collaborations with many research groups. Prof. Field and Dr. Jacobson have developed two powerful pattern recognition techniques to process the enormous, high quality, multispectral data sets generated in modern laser spectroscopy experiments. Hybrid linear pattern analysis combines extended cross correlation with least squares fitting; robust baseline estimation optimally combines robust estimator and least squares procedures. This research has provided crucial insights into intramolecular vibrational redistribution processes in acetylene and the mechanism of surface electron ejection by laser-excited metastable molecules.
Professors Field and Steinfeld, in collaboration with Dr. Alexander Kachanov, have studied developed new variants of cavity ringdown and intracavity laser absorption spectroscopy (ICLAS), two ultrasensitive absorption techniques. The new schemes provide quantum limited sensitivity and are ideal for UV and IR applications, where high reflectance mirrors are often not available, and for double resonance studies. Using ICLAS. Professors Steinfeld and Field, along with Drs. Shengfu Yang, Manjula Canagaratna, and Kachanov, have carried out careful measurement of line intensities and self-broadening coefficients in the oxygen A-band. Using a double-time-correlated ICLAS technique, they have detected photolysis products from the flash-decomposition of acrylonitrile.
Professor Bawendi and Dr. Robert Neuhauser have designed and developed an apparatus for the highly parallel study of the spectroscopy of individual quantum dots. This allows hundreds of dots to be observed simultaneously in both image and spectral mode. A correlation between fluorescence intermittency and spectral diffusion was observed. Fluorescence polarization studies showed that far-field polarization microscopy can determine the 3 dimensional orientation of individual quantum dots.
Professor Mildred Dresselhaus and Drs. Gene Dresselhaus, Paola Corio, Alessandra Marucci and Marcos Pimenta using resonance Raman spectroscopy, have observed differences in behavior between semiconducting and metallic single-walled carbon nanotubes in first and higher-order spectra. Surface-enhanced resonance and non-resonance Raman spectroscopy of these structures are in progress, with the aim of studying single carbon nanotubes.
Professor Feld and Drs. Dasari and Chung-Chieh Yu continued their work on the cavity-QED laser. They have redesigned the system to study nonclassical behavior of this atom-cavity system in the mesoscopic region. A new atomic oven has improved both the density and stability of the atomic beam, and a specially designed slit has provided greater uniformity of the atom-cavity coupling strength.
Professors Tanaka and Feld are developing polymer gels that can recognize a molecule and reversibly change its affinity by orders of magnitude, constituting the first evidence of structure memory by polymers. Affinities were quantified using UV and fluorescence spectroscopy. Polymer gels that decompose hydrogen peroxide and thus behave as artificial enzymes have also been developed. Spectroscopic analysis will be carried out to determine the catalysis.
Professor Lippard and his colleagues have used resonance Raman spectroscopy to characterize synthetic models of metalloenzyme active sites. A model for the non-heme diiron (II) site in hemerythrin, a dioxygen carrier in marine invertebrates, was synthesized by Dr. Tadashi Mizoguchi, and the dioxygen adduct characterized.
Drs. Jayanti Pande of the Department of Physics and Ramasamy Manoharan have compared Raman spectra of native and oxidized bovine B crystallins in vibrational regions characteristic of thiol (-SH) and disulfide (-S-S-) groups, and shown that disulfide formation does not lead to significant secondary structural changes. Drs. Pande and Eugene Hanlon are studying recombinant mutant B crystallins in which a Cys residue is replaced by a Ser residue, with the goal of correlating oxidation of individual Cys residues with changes in their hydrogen-bonding environment within the protein. Understanding such systems is relevant to the process of oxidative stress, a major cause of cataracts.
Professor Tannenbaum and Drs. Paul Skipper, Can Özbal and Dasari have developed a method using ultrasensitive HPLC with laser-induced fluorescence to quantify benzo[a]pyrene (BP) adducts in human serum albumin. In a pilot epidemiological study, albumin from 63 healthy women was analyzed for BP adduct content. BP adducts were detected in 95.2 percent of samples at a median level of 0.16 fmol adduct per mg albumin. Further work will expand the number of subjects and types of carcinogens.
Professor Jonathan King and Drs. Stephen Raso and Hanlon are using Raman spectroscopy to monitor conformational changes in the protein granulocyte-colony stimulating factor (G-CSF). G-CSF is an important therapeutic agent, but drug delivery is hampered by the protein's propensity to precipitate under physiological conditions. The precipitation mechanism is being probed by monitoring changes in the SH stretch and amides I and III during the early stages of the process.
Professor Alexander Rich and Drs. Imre Berger and Manoharan established that a human protein, ds RNA deminase (ds RAD) has specificity for binding Z-DNA. Raman spectra of poly (GC) in low and high salt solutions, control protein and protein/poly (GC) complex were obtained, and spectral features of left and right-handed DNA conformers were characterized. By comparing these with the spectra of the protein/poly (GC) complex, it was concluded that DNA exists in the left-handed conformer when it binds to ds RAD.
Professor Feld and Drs. Dasari, Rajan Gurjar, Hanlon, Irving Itzkan, Lev Perelman and Qingguo Zhang are pursuing basic and applied applications of lasers and spectroscopy in biology and medicine. Reflectance, fluorescence, coherent and acousto-optical techniques, and near-IR Raman spectroscopy are being used for biochemical analysis of tissues and diagnosis of disease. Clinical studies are being conducted with researchers from the Cleveland Clinic Foundation, Brigham and Women's Hospital, Metrowest Hospital, Beth Israel Hospital and New England Medical Center. Highlights include: (1) Demonstration that Raman spectroscopy can accurately measure concentrations of glucose and other blood analytes in serum and blood at physiological levels. (2) Clinical demonstration of a light scattering technique to detect the precancerous condition known as dysplasia, accomplished by determining the size distribution of epithelial cell nuclei. (3) The use of fluorescence spectroscopy of brain tissue to identify Alzheimer's disease, and in colon, bladder, and oral cavities to identify precancerous states of tissue. (4) The use of Michelson interferometry to study the interplay of stress waves and cavitation in soft biological tissues, induced by short pulses of laser light. (5) The use of heterodyne detection to study forward-scattered light propagating in a turbid medium (such as biological tissue); the degree of spatial coherence was significantly higher for singly-scattered photons, and found to approach a small constant value for a large number of scattering events. The experimental and theoretical work being of this program is advancing new laser diagnostic technologies in the field of medicine.
More information about the Laboratory can be found on the World Wide Web at http://web.mit.edu/spectroscopy/.
Michael S. Field
MIT Reports to the President 1998-99