Our research interests span a range of topics that have to do with IR and Raman spectroscopy applied to thin films, imaging of surfaces and interfaces using fluorescent and scanning probe methods, biophysical chemistry, spectroscopy of membrane models, and the development of novel spectroscopic-based methods for biosensing. Click on some of the following links to learn more about the specific research areas studied in our group.
Molecular Biophysics Research Projects
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Infrared Reflection-Absorption Spectroscopy of Monolayer Films |
Infrared Reflectance-Absorption Spectroscopy of Monolayer Films
Organized two-dimensional organic films at interfaces have become an important component in a wide variety of disciplines, including non-linear optics, sensors, catalysis, surface modification, electrode coatings, and biomacromolecules. Our interests are in the class of amphiphilic monomolecular films that form ordered two-dimensional arrays at the air-water (A/W) interface. Insoluble monolayers at the A/W interface have been extensively studied as models for ionic, dipolar and interfacial phenomena in chemical systems (e.g. surfactants and polymers) as well as in biophysical systems (e.g. proteins, steroids and membranes). Our group was the first to develop an infrared reflectance method that is able to give direct information on monolayer structure. This technique is highly surface-sensitive, due to the fact that vibrational spectroscopy measures changes in the permanent dipole moment of specific functional groups in the surface-absorbed molecule, which can then be related to the unique conformation or configuration of the functional group at the interface.
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Click here for information about our monolayer IR apparatus. |
Epi-Fluorescence Microscopic Imaging
We are currently using a combined approach for the study of ultrathin Langmuir films at the A/W interface that utilizes infrared spectroscopy and epi-fluorescence imaging. As described above, IR spectroscopy has shown itself to be an effective tool in the study of structural conformation in monomolecular films at the A/W interface. In addition, fluorescence microscopy is an important and widely used method for imaging the morphology of these Langmuir monolayers, and has the advantage of providing information on real-space, two-dimensional structure and morphology at mesoscopic (i.e. micrometer) resolution scales.
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Click here for information about our epi-fluoresecence monolayer experiments. |
Scanning Probe Imaging of Ultrathin Films
New techniques in scanning probe microscopy, primarily scanning tunneling and atomic force microscopies (i.e. STM and AFM), have over the last several years been increasingly used to determine the structure of monomolecular films at interfaces. The advantage of these techniques is that one may now image ultrathin films in order to identify intrinsic topological features in these two-dimensional solids. We are currently developing a combined method of using both vibrational spectroscopy and scanning probe microscopy to study Langmuir-Blodgett and self-assembled monomolecular films on surfaces. The combination of the two techniques has the potential to significantly improve our understanding of the formation, structure, and reactivity of ultrathin films. We have developed methods to produce conducting, atomically flat, Ge substrates and are using this new material to study interfacial organic monolayers by STM, AFM and IR. Currently, we are using a combination of IR and AFM to study organized bilayer systems on Au and Ge.
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Click here for images from our scanning probe experiments. |
We are interested in the use of monolayer spectroscopy for the study of biophysical applications such as peptide recognition and translocation through membranes. In particular, we have an interest in using these techniques to study pulmonary surfactant. Pulmonary surfactant is a lipid-protein complex secreted by type II cells of the pulmonary alveolus, and functions to reduce surface tension at the A/W interface in the lung. A monomolecular film of phospholipid is generally believed to be the physiologically relevant configuration of the pulmonary surfactant at the A/W interface in the lung under high levels of surface film compression. We have published infrared studies of pulmonary surfactant components both alone and in mixed monolayers. Current work has focused on using a combined IR/microscopy approach to study model systems that describe functional relationships among surfactant components.
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Click here for more information on our surfactant studies |
Liquid Chromatography of Surfactant Components
Using 31P NMR spectroscopy, we discovered a new, previously unknown, phospholipid component in natural mammalian pulmonary surfactant. We have recently expanded this line of research to develop a liquid chromatographic method for separation of these phospholipid components using gradient elution high performance liquid chromatography coupled with an evaporative light scattering detector. The advantage of this method is that it can separate individual molecular phospholipid species using ng’s of injected material without additional derivatization steps.
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Click here for chromatograms from our LC-ELSD instrument. |
Molecularly Engineered Biomaterials
We are currently collaborating with Dr. Elliot Chaikof and his group at Emory University Medical School in Atlanta to analyze molecularly-engineered surfaces for potential applications such as sensors or bio-functional coatings for artificial organs and other implanted medical devices. We study these surfaces using IR, Raman and fluorescence microscopy to deduce structure and the molecular-level details needed to increase the robustness and stability of these systems.
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Click here for information about our biomaterials research projects. |
Two-dimensional infrared (2D IR) correlation spectroscopy is a mathematical means of treating spectral data sets in which the dynamic spectral variations induced by an external perturbation are subject to statistical cross-correlation. 2D IR has particular advantages in simplifying complex spectra, identifying inter- and intramolecular interactions, and facilitating band assignments. We are currently developing new 2D IR methods for resolution enhancement and determination of the temporal order of events in sets of dynamic spectra. Our methods use model-dependent correlations that more quantitatively reveal the relative rates of motion in these dynamic time-resolved spectra.
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Click here for information about our 2D-IR experiments. |
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Biomedical Sensing Using SERS |
Raman Spectroscopy of Thin Films
We are currently developing a Raman spectroscopic approach to the study of thin films and monolayers that will complement our IR and fluorescence studies in this area. Our thin film Raman experiment is built around Argon and Ti:Sapphire lasers, 0.5 meter monochromator, holographic Raleigh rejection filters and CCD detector. In addition, we have recently purchased a fiber-optic interfaced Raman microscope that we will use to acquire the spectra of these Langmuir and Langmuir-Blodgett thin films. The advantage of Raman spectroscopy for these studies is in the superior wavelength coverage of Raman vs. IR as well as the weak Raman scattering of water, which allows us to study regions which are difficult or inaccessible using reflection IR spectroscopy.
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Click here for diagrams and spectra from our Raman monolayer apparatus. |
SERS of Novel Nanostructured Materials
We are currently utilizing Surface-Enhanced Raman Spectroscopy (SERS) as a powerful tool for the investigation and characterization of interfacial and thin-film systems. In spite of its popularity, SERS does have limitations, including strict requirements for substrate morphology that must be met in order to achieve optimal enhancement. Our work uses a nanofabrication technique known as glancing angle vapor deposition (GLAD) to produce nanorod arrays with varying rod lengths. Our work lies in both the fundamental properties of nanorod arrays as SERS substrates, and the use of these substrates as sensors for the solution of chemical and biological problems.
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Click here for information about our SERS experiments. |
We are currently utilizing Surface-Enhanced Raman Spectroscopy (SERS) as a powerful tool for the characterization of biomedically important pathogens. Development of diagnostic methods for rapid and sensitive identification of pathogens is essential for the advancement of therapeutic and preventive intervention strategies necessary to protect public health. Current diagnostic methods, which may include virus isolation, PCR, antigen detection and serology, can be time-consuming, cumbersome, or lack the required sensitivity. Our spectroscopic-based SERS sensing methods have potential advantages in terms of both sensitivity and selectivity.
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Click here for information about our biomedical SERS experiments. |